Guide to electrical safety

              A Guide to

Electrical Safety

N. C. Department of Labor

Occupational Safety and Health Division

1101 Mail Service Center

Raleigh, NC 27699- 1101

Cherie Berry

Commissioner of Labor

              	


        

18

N. C. Department of Labor

Occupational Safety and Health Program

Cherie Berry

Commissioner of Labor

OSHA State Plan Designee

Allen McNeely

Deputy Commissioner for Safety and Health

Kevin Beauregard

Assistant Deputy Commissioner for Safety and Health

Edward E. Lewis

Reviewer

Acknowledgments

A Guide to Electrical Safety was prepared by Ed Mendenhall of Mendenhall Technical Services with additional materi-als

provided by N. C. Department of Labor employee Dwight Grimes. The information in this guide was updated in

2008.

This guide is intended to be consistent with all existing OSHA standards; therefore, if an area is considered by the

reader to be inconsistent with a standard, then the OSHA standard should be followed.

To obtain additional copies of this guide, or if you have questions about North Carolina occupational safety and health stan-dards

or rules, please contact:

N. C. Department of Labor

Education, Training and Technical Assistance Bureau

1101 Mail Service Center

Raleigh, NC 27699- 1101

Phone: ( 919) 807- 2875 or 1- 800- NC- LABOR

____________________

Additional sources of information are listed on the inside back cover of this guide.

____________________

The projected cost of the NCDOL OSH program for federal fiscal year 2009– 2010 is $ 17,534,771. Federal funding provides approximately 30 percent ($ 5,180,700) of

this fund.

Revised 2/ 08

Contents

Part Page

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1iiv

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivi1

2 Fundamentals of Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii14

3 Arc Flash/ NFPA 70E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii11

4 Branch Circuit Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii13

5 Branch Circuit and Equipment Testing . . . . . . . . . . . . . . . . . . . . . . . . . ii21

6 Voltage Detector Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii24

7 Ground Fault Circuit Interrupters . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii26

8 Common Electrical Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii43

9 Inspection Guidelines/ Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii57

10 Safety Program Policy and Procedures . . . . . . . . . . . . . . . . . . . . . . . . . ii59

iii

Foreword

Everyone from office clerks to farmers work around electricity on a daily basis. Our world is filled with overhead

power lines, extension cords, electronic equipment, outlets and switches. Our access to electricity has become so common

that we tend to take our safety for granted. We forget that one frayed power cord or a puddle of water on the floor can

take us right into the electrical danger zone.

A Guide to Electrical Safety can help electricians, plant maintenance personnel and many others review safe proce-dures

for electrical work. It also covers the main U. S. Occupational Safety and Health Administration standards concern-ing

electrical safety on the job.

In North Carolina, state inspectors enforce the federal laws through a state plan approved by the U. S. Department of

Labor. The N. C. Department of Labor is charged with this mission. NCDOL enforces all current OSHA standards. It

offers many educational programs to the public and produces publications, including this guide, to help inform people

about their rights and responsibilities.

When reading this guide, please remember the NCDOL mission is greater than enforcement of regulations. An equally

important goal is to help citizens find ways to create safer workplaces. A Guide to Electrical Safety can help you make

and keep your workplace free of dangerous electrical hazards.

Cherie Berry

Commissioner of Labor

v

1

1

Introduction

Electricity is the modern version of the genie in Aladdin’s lamp. When electricity is safely contained in an insulated

conductor, we normally cannot see, smell, taste, feel or hear it. It powers an endless list of laborsaving appliances and

life- enhancing and support systems that have become such an assumed part of our lives that we give little thought to its

potential for causing harm. Many myths and misstatements about electrical action are accepted as fact by many people.

The National Institute for Occupational Safety and Health ( NIOSH) conducted a study of workplace electrocutions that

revealed the following information about workers who were electrocuted:

• The average age was 32.

• 81 percent had a high school education.

• 56 percent were married.

• 40 percent had less than one year of experience on the job to which they were assigned at the time of the fatal acci-dent.

• 96 percent of the victims had some type of safety training, according to their employers.

This information reminds us that more effective training and education must be provided to employees if we are to

reduce workplace electrocution hazards. Employees should receive initial training then refresher electrical hazard recog-nition

training on an annual basis.

In addition to the shock and electrocution hazards, electricity can also cause fires and explosions. According to the U. S.

Consumer Product Safety Commission, an estimated 169,000 house fires of electrical origin occur each year, claiming

1,100 lives and injuring 5,600 people. Property losses from fires begun by electricity are estimated at $ 1.1 billion each

year. The safe use and maintenance of electrical equipment at work ( and at home) will help prevent fire and physical injury.

This guide provides a clear understanding of electrical action and its control in the workplace environment. This infor-mation

will enable you to recognize electrical hazards in the workplace as well as provide information on their control

and/ or elimination. The guide does not qualify a person to work on or near exposed energized parts. Training

requirements for “ qualified” persons ( those permitted to work on or near exposed energized parts) are detailed in

29 CFR 1910.332( b)( 3). Also, 29 CFR 1910.399, Definitions Applicable to Subpart S gives a definition of “ qualified

person.” The guide will, however, enhance your ability to find and report electrical deficiencies in need of a quali-fied

person’s attention.

Dangers of Electricity

Whenever you work with power tools or on electrical circuits, there is a risk of electrical hazards, especially electrical

shock. Anyone can be exposed to these hazards at home or at work. Workers are exposed to more hazards because job-sites

can be cluttered with tools and materials, fast- paced, and open to the weather. Risk is also higher at work because

many jobs involve electric power tools.

Electrical trades workers must pay special attention to electrical hazards because they work on electrical circuits.

Coming in contact with an electrical voltage can cause current to flow through the body, resulting in electrical shock and

burns. Serious injury or even death may occur. As a source of energy, electricity is used without much thought about the

hazards it can cause. Because electricity is a familiar part of our lives, it often is not treated with enough caution. As a

result, an average of one worker is electrocuted on the job every day of every year. Electrocution is the third leading cause

of work- related deaths among 16- and 17- year- olds, after motor vehicle deaths and workplace homicide. Electrocution is

the cause of 12 percent of all workplace deaths among young workers. 1

____________

1 Castillo D. N. [ 1995]. NIOSH Alert: Preventing Death and Injuries of Adolescent Workers. Cincinnati, Ohio: U. S. Department of Health and Human Services, Public

Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS ( NIOSH) Publication No. 95- 125.

• Electrical shock causes injury or death!

• current— the movement of electrical charge

• voltage— a measure of electrical force

• circuit— a complete path for the flow of current

• You will receive a shock if you touch two wires at different volt-ages

at the same time.

This industry guide offers discussion on a variety of topics as pertained

to electrical hazards. There are four main types of electrical injuries: elec-trocution

( death due to electrical shock), electrical shock, burns and

falls. The guide discusses the dangers of electricity, electrical shock and

the resulting injuries. It describes the various electrical hazards. The guide includes a sample plan ( Safety Model) or

approach to address these hazards in a later section. ( This sample model/ approach is also useful with other hazards.) You

will learn about the Safety Model, as an important tool for recognizing, evaluating and controlling hazards. The guide

includes important definitions and notes are shown throughout. It emphasizes practices that will help keep you safe and

free of injury. It also includes case studies about real- life deaths to give you an idea of the hazards caused by electricity.

How Is an Electrical Shock Received?

An electrical shock is received when electrical current passes through the body. Current will pass through the body in a

variety of situations. Whenever two wires are at different voltages, current will pass between them if they are connected.

Your body can connect the wires if you touch both of them at the same time. Current will pass through your body.

• ground— a physical electrical connection to the earth

• energized ( live, “ hot”)— similar terms meaning that a voltage is present that can cause a

current, so there is a possibility of getting shocked

In most household wiring, the black wires and the red wires are at 120 volts. The white wires are

at 0 volts because they are connected to ground. The connection to ground is often through a con-ducting

ground rod driven into the earth. The connection can also be made through a buried metal

water pipe. If you come in contact with an energized black wire— and you are also in contact with

the neutral white wire— current will pass through your body. You will receive an electrical shock.

• conductor— material in which an electrical current moves easily

• neutral— at ground potential ( 0 volts) because of a connection to ground

If you are in contact with a live wire or any live component

of an energized electrical device— and also in contact with any

grounded object— you will receive a shock. Plumbing is often

grounded. Metal electrical boxes and conduit are grounded.

Your risk of receiving a shock is greater if you stand in a

puddle of water. But you don’t even have to be standing in

water to be at risk. Wet clothing, high humidity and perspiration

also increase your chances of being shocked. Of course, there is

always a chance of shock, even in dry conditions. You can even

receive a shock when you are not in contact with an electrical

ground. Contact with both live wires of a 240- volt cable will

deliver a shock. ( This type of shock can occur because one live

wire may be at + 120 volts while the other is at – 120 volts dur-ing

an alternating current cycle— a difference of 240 volts.) You

can also receive a shock from electrical components that are not

grounded properly. Even contact with another person who is

receiving an electrical shock may cause you to be shocked.

2

Electrical work can be deadly if not done safely.

Wires carry current.

Metal electrical boxes should

be grounded to prevent shocks.

Black and red wires are

usually energized, and

white wires are usually

neutral.

• You will receive a shock if you touch a live wire and are grounded at the same time.

• When a circuit, electrical component or equipment is energized, a potential shock haz-ard

is present.

Summary

You will receive an electrical shock if a part of your body completes an electrical circuit by

touching a live wire and an electrical ground, or touching a live wire and another wire at a differ-ent

voltage.

3

Always test a circuit

to make sure it is

de- energized before

working on it.

2

Fundamentals of Electricity

A review of the fundamentals of electricity is necessary to an understanding of some common myths and misstate-ments

about electricity. First we must review Ohm’s Law and understand the effects of current on the human body. Basic

rules of electrical action will enhance your ability to analyze actual or potential electrical hazards quickly. This informa-tion

will also enable you to understand other important safety concepts such as reverse polarity, equipment grounding,

ground fault circuit interrupters, double insulated power tools, and testing of circuits and equipment.

Ohm’s Law

There are three factors involved in electrical action. For electrons to be activated or caused to flow, those three factors

must be present. A voltage ( potential difference) must be applied to a resistance ( load) to cause current to flow when there

is a complete loop or circuit to and from the voltage source. Ohm’s Law simply states that 1 volt will cause a current of 1

ampere to flow through a resistance of 1 ohm. As a formula this is stated as follows:

Voltage ( E) = Current ( I) X Resistance ( R).

We will be concerned about the effects of current on the human body, so the formula relationship we will use most will

be I = E/ R. When you analyze reported shock hazards or electrical injuries, you should look for a voltage source and a

resistance ( high or low) ground loop. The human body is basically a resistor and its resistance can be measured in ohms.

Figure 1 depicts a body resistance model. The resistive values are for a person doing moderate work. An increase in per-spiration

caused from working at a faster work pace would decrease the resistance and allow more current to flow.

As an example, let’s use the hand to hand resistance of the body model, 500 + 500

= 1,000 ohms. Using I = E/ R, I = 120/ 1,000 ( assuming a 120 volt AC ( alternating

current) power source) or 0.120 amps. If we multiply 0.120 amps by 1,000 ( this con-verts

amps to milliamps), we get 120 milliamps ( mA) which we will refer to in

Figure 2. If a person were working in a hot environment, and sweating, the body

resistance could be lowered to a value of 500 ohms. Then the current that could flow

through the body would equal I = 120/ 500 or 0.240 amps. Changing this to mil-liamps,

1,000 X 0.240 = 240 mA. This means that we have doubled the hazard to the

body by just doing our job.

This can be explained by looking at Figure 2. Figure 2 plots the current flowing

through the chest area and the time it takes to cause the heart to go into ventricular

fibrillation

( arrhythmic

heartbeat).

Using the

example of

the body

resistance at

1,000 ohms allowing 120 mA to flow ( follow

the dark line vertically from 120 mA to the

shaded area, then left to the time of 0.8 seconds),

you can see that it would only take 0.8 seconds

to cause electrocution. When the body resistance

is 500 ohms, at 240 mA it would only take 0.2

seconds to cause electrocution. Variable condi-tions

can make common- use electricity ( 110

volts, 15 amps) fatal.

4

               

       

               

Figure 1

Human Body Resistance Model

10.0

6.0

2.0

1.0

0.6

.2

.1

.06

.02

.01

Time In Seconds

‘ Let Go’

Range

Maximum Permitted

By UL For Class A GFCI

Electrocution Threshold

For Typical Adult

0 20 40 60 80 100 120 140 160 180 200 220 240 260

Current In Milliamperes

Figure 2

Electrical Current ( AC) Versus the Time It Flows Through the Body

Current and Its Effect on the Human Body

Based on the research of Professor Dalziel of the University of California, Berkeley, the effect of 60 Hz ( cycles per

second) of alternating current on the human body is generally accepted to be as follows:

• 1 milliamp ( mA) or less— no sensation— not felt ( 1,000 milliamps equal 1 amp)

• 3 mA or more painful shock

• 5 mA or more— local muscle contractions— 50 percent cannot let go

• 30 mA or more— breathing difficult— can cause unconsciousness

• 50– 100 mA— possible heart ventricular fibrillation

• 100– 200 mA— certain heart ventricular fibrillation

• 200 mA or more— severe burns and muscular contractions— heart more apt to stop than fibrillate

• Over a few amps— irreversible body damage

Thus, we can see that there are different types of injuries that electricity can cause. At the 20 to 30 mA range a form of

anoxia ( suffocation) can result. This could happen in a swimming pool where there is a ground loop present ( the drain at the

bottom of the pool) if a faulty light fixture or appliance is dropped into the water. Current would flow from the light fixture

to the drain, using the water as the conducting medium. Any person swimming through the electrical field created by the

fault current would be bathed in potential difference, and the internal current flow in the body could paralyze the breathing

mechanism. This is why it is very important to keep all portable electrical appliances away from sinks, tubs and pools.

Ventricular fibrillation generally can occur in the range of 50 to 200 mA. Ventricular fibrillation is the repeated, rapid,

uncoordinated contractions of the ventricles of the heart resulting in the loss of synchronization between the heartbeat and

the pulse beat. Once ventricular fibrillation occurs, death can ensue in a few minutes. Properly applied CPR ( cardiopul-monary

resuscitation) techniques can save the victim until emergency rescue personnel with a defibrillator arrive at the

scene. Workers in the construction trades and others working with electrical power tools should receive CPR training.

Above a few amperes, irreversible body damage can occur. This condition is more likely to occur at voltages above

600 volts AC. For example, if a person contacted 10,000 volts, I = 10,000/ 1,000 = 10 amps. This amount of current would

create a great amount of body heat. Since the body consists of over 60 percent water, the water would turn to steam at a

ratio of approximately 1 to 1,500. This would cause severe burns or exploding of body parts. These are the types of

injuries that you would normally associate with electric power company workers. They can also occur, however, when

people accidentally let a television or radio antenna contact an uninsulated power line. Accidents involving mobile verti-cal

scaffolding or cranes booming up into power lines can cause these types of injuries or fatalities.

The route that the current takes through the body affects the degree of injury. If the current passes through the chest

cavity ( e. g., left hand to right hand), the person is more likely to receive severe injury or electrocution; however, there

have been cases where an arm or leg was burned severely when the extremity came in contact with the voltage and the

current flowed through a portion of the body without going through the chest area of the body. In these cases the person

received a severe injury but was not electrocuted.

Typical 120 Volt AC System

At some time in your life, you

may have received an electrical

shock. Figure 3 illustrates a typical

120 volt AC system. Somewhere

near your home or workplace there

is a transformer with wires going

between the transformer and the ser-vice

entrance panel ( SEP). In small

establishments and homes, the SEP

may also contain circuit breakers or

fuses to protect the circuits leaving

the SEP. Typical overcurrent protec-tion

for these circuits would be 15 or

20 amps. This protection is designed

5

120 Volts

120 Volts

Neutral

Grounding Electrode

Equipment- grounding

Conductor ( green or bare)

Utility

Supply

Service

Ground

Circuit Breaker

Grounded

Conductor

( white or gray)

“ Hot” Conductor

( black or red)

Primary Lines

2.4– 13 kV

Figure 3

AC Systems— Contact With “ Hot” Conductor

for line ( hot) to line ( grounded conductor) faults that would cause current greater than 15 or 20 amps to flow. If a person

accidentally contacted the “ hot��� conductor while standing on the ground with wet feet ( see Figure 3), a severe shock could

result. Current could flow through the body and return to the transformer byway of the “ ground loop” path. Most electrical

shocks result when the body gets into a ground loop and then contacts the “ hot” or ungrounded conductor. If you analyze

electrical shock incidents, look for these two factors: a ground loop and a voltage source.

We normally think of ground as the earth beneath our feet. From an electrical hazard standpoint, ground loops are all

around us. A few ground loops that may not be under our feet include metal water piping, metal door frames in newer

building construction, ventilation ducts, metal sinks, metal T- bars holding ceiling acoustical panels, wet or damp concrete

floors and walls, grounded light fixtures, and grounded power tools/ appliances. When you are using or working around

electrical equipment, be alert to these and other ground loops. The person shown in Figure 3 could have isolated the

ground loop by standing on insulated mats or dry plywood sheets. Wearing dry synthetic soled shoes would also have iso-lated

the ground loop.

The utility supply ground and the grounding electrode conductor are system safety grounds. These grounds protect the

users of electrical equipment in case of lightning storms and in instances where high voltage lines accidentally fall on

lower voltage lines. These system safety grounds are not designed for individual safety. Actually, they are a hazard to the

individual in that it is very easy to get into a ground loop, and once into a ground loop, you only need one fault path to the

hot conductor before shock or injury can result.

Four Principles of Electrical Action

Knowing the basic principles of electrical action will help you understand and evaluate electrical shock hazards. These

principles and an explanation for each are as follows:

1. Electricity does not “ spring” into action until current flows.

2. Current will not flow until there is a loop ( intentionally or accidentally) from the voltage source to a load and back

to the source.

3. Electrical current always returns to the voltage source ( transformer) that created it.

4. When current flows, energy ( measured in watts) results.

Explanation for Principle 1

A person can contact voltage and not be shocked if there is high resistance in the loop. In Figure 3, the person is stand-ing

on the ground and touching the 120 volt conductor. That would cause a shock and make your hair stand on end. If that

same person were standing on insulated mats or wore shoes with insulated soles, the person would not be shocked even

though there was 120 volts in his or her body. This explains why a person can be working outside with a defective power

tool and not receive a shock when the ground is very dry or the person is isolated from a ground loop by plywood. That

same person with the same power tool could change work locations to a wet area, then receive a shock when contacting a

ground loop of low resistance. As previously stated, 3 mA or more can cause painful shock. Using Ohm’s Law I = E/ R,

120 volts and 3 mA, we can calculate how much resistance would allow 3 mA of current to flow. R = E/ I or 120/ 0.003 or

R = 40,000 ohms. Any ground loop resistance of less than 40,000 ohms would allow a shock that could be felt. This prin-ciple

can also explain why birds sitting on a power line are not electrocuted. Their bodies would receive voltage, but cur-rent

would not flow since another part of their body is not in contact with a ground loop.

Explanation for Principle 2

For current to flow, a complete loop must be established from the voltage source to the person and back to the voltage

source. In Figure 3, the loop is through the person’s hand touching a 120 volt conductor, through the body to ground and

then through the grounding electrode and back to the transformer secondary through the neutral conductor. Once that loop

is established and becomes less than 40,000 ohms, a shock or serious injury can result. If the loop can be interrupted, as

noted in Principle 1, then current will not flow. These two principles give you a common sense way to figure out how and

why someone received a shock and the action that should be taken to prevent future shocks of the same type.

Explanation for Principle 3

Electric current always seeks to return to the transformer that created it. Current will also take all resistive paths to

return to the transformer that created it. Since the voltage source has one wire already connected to ground ( Figure 3),

6

contact with the “ hot” wire provides a return path for current to use. Other ground loop paths in the workplace could

include metal ducts, suspended ceiling T- bars, water pipes and other similar ground loops.

Explanation for Principle 4

This principle explains the shock and injury to the human body that current can do. The higher the voltage involved,

the greater the potential heat damage to the body. As previously mentioned, high voltage can cause high current flow

resulting in severe external and internal body damage. Remember that the flow of current causes death or injury; voltage

determines how the injury or death is effected.

Some Misconceptions About Electrical Action

Americans use more electrical power per person than do individuals of any other country in the world, but that does

not mean that we have a better understanding of electricity. Some common misconceptions about electrical actions are

addressed and corrected in the following discussion.

“ If an Appliance or Power Tool Falls Into Water, It Will Short Out���

When an appliance falls into a tub or container of water, it will not short out. In fact, if the appliance switch is “ on,” the

appliance will continue to operate. If the appliance has a motor in it, the air passage to keep the motor cool will be water

cooled. Unfortunately, that same air passage, when wet, will allow electricity to flow outside the appliance if a current

loop is present ( such as a person touching the metal faucet and reaching into the water to retrieve a hair dryer). The cur-rent

loop due to the water resistance will be in the 100 to 300 mA range, which is considerably less than the 20,000+ mA

needed to trip a 20 amp circuit breaker. Since an appliance will not short out when dropped in a sink or tub, no one should

ever reach into the water to retrieve an appliance accidentally dropped there. The water could be electrified, and a person

touching a grounded object with some other part of the body could receive a serious shock depending on the path the cur-rent

takes through the body. The most important thing to remember is that appliances do not short out when dropped or

submerged in water.

“ Electricity Wants to Go to the Ground”

Sometimes editors of motion films about electrical safety make the statement that “ electricity wants to go to the

ground.” There are even books published about electrical wiring that contain the same statement. As previously stated,

electricity wants to return to the transformer that created it, and the two conductors that were designed to carry it safely

are the preferred route it takes. Whenever current goes to ground or any other ground loop, it is the result of a fault in the

appliance, cords, plugs or other source.

“ It Takes High Voltage to Kill; 120 Volts AC Is Not Dangerous”

Current is the culprit that kills. Voltage determines the form of the injury. Under the right conditions, AC voltage as

low as 60 volts can kill. At higher voltages the body can be severely burned yet the victim could live. Respect all AC

voltages, high or low, as having the potential to kill.

“ Double Insulated Power Tools Are Doubly Safe and Can Be Used in Wet and Damp Locations”

Read the manufacturer’s operating instructions carefully. Double insulated power tools are generally made with materi-al

that is nonconductive. This does give the user protection from electrical faults that occur within the insulated case of

the appliance. However, double insulated power tools can be hazardous if dropped into water. Electrical current can flow

out of the power tool case into the water. Remember that double insulated power tools are not to be used in areas where

they can get wet. If conditions or situations require their use under adverse conditions, use GFCI ( ground fault circuit

interrupter) protection for the employee.

• ampere ( amp)— the unit used to measure current

• milliampere ( milliamp or mA)— 1/ 1,000 of an ampere

• shocking current— electrical current that passes through a part of the body

• You will be hurt more if you can’t let go of a tool giving a shock.

• The longer the shock, the greater the injury.

7

Dangers of Electrical Shock

The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current

passes through the body. For example, 1/ 10 of an ampere ( amp) of electricity going through the body for just 2 seconds is

enough to cause death. The amount of internal current a person can withstand and still be able to control the muscles of the

arm and hand can be less than 10 milliamperes ( milliamps or mA). Currents above 10 mA can paralyze or “ freeze” muscles.

When this “ freezing” happens, a person is no longer able to release a tool, wire or other object. In fact, the electrified object

may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, hand- held tools that give

a shock can be very dangerous. If you can’t let go of the tool, current continues through your body for a longer time, which

can lead to respiratory paralysis ( the muscles that control breathing cannot move). You stop breathing for a period of time.

People have stopped breathing when shocked with currents from voltages as low as 49

volts. Usually, it takes about 30 mA of current to cause respiratory paralysis.

Currents greater than 75 mA cause ventricular fibrillation ( very rapid, ineffective

heartbeat). This condition will cause death within a few minutes unless a special device

called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which

means the heart does not pump at all. Tissue is burned with currents greater than 5 amps. 2

Table 1 shows what usually happens for a range of currents ( lasting one second) at

typical household voltages. Longer exposure times increase the danger to the shock vic-tim.

For example, a current of 100 mA applied for 3 seconds is as dangerous as a cur-rent

of 900 mA applied for a fraction of a second ( 0.03 seconds). The muscle structure

of the person also makes a difference. People with less muscle tissue are typically

affected at lower current levels. Even low voltages can be extremely dangerous because

the degree of injury depends not only on the amount of current but also on the length of

time the body is in contact with the circuit.

LOW VOLTAGE DOES NOT MEAN LOW HAZARD!

Table 1

Effects of Electrical Current* on the Body3

8

Defibrillator in use.

Current Reaction

1 milliamp Just a faint tingle.

5 milliamps Slight shock felt. Disturbing, but not painful. Most people can let go.

However, strong involuntary movements can cause injuries.

6– 25 milliamps ( women)† Painful shock. Muscular control is lost. This is the range where " freezing currents" start.

9– 30 milliamps ( men) It may not be possible to let go.

5– 150 milliamps Extremely painful shock, respiratory arrest ( breathing stops), severe muscle contractions.

Flexor muscles may cause holding on; extensor muscles may cause intense pushing

away. Death is possible.

1,000– 4,300 milliamps Ventricular fibrillation ( heart pumping action not rhythmic) occurs. Muscles contract;

( 1– 4.3 amps) nerve damage occurs. Death is likely.

10,000 milliamps Cardiac arrest and severe burns occur. Death is probable.

( 10 amps)

15,000 milliamps Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!

( 15 amps)

* Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns.

† Differences in muscle and fat content affect the severity of shock.

____________

2 Lee R. L. [ 1973]. Electrical Safety in Industrial Plants. Am Soc Safety Eng J18( 9): 36- 42.

3 USDOL [ 1997]. Controlling Electrical Hazards. Washington, D. C.: U. S. Department of Labor, Occupational Safety and Health Administration.

Sometimes high voltages lead to additional injuries. High voltages can cause violent muscular contractions. You may

lose your balance and fall, which can cause injury or even death if you fall into machinery that can crush you. High volt-ages

can also cause severe burns ( as seen on photos later in this and other sections).

• High voltages cause additional injuries.

At 600 volts, the current through the body may be as great as 4 amps, causing damage to internal organs such as the

heart. High voltages also produce burns. In addition, internal blood vessels may clot. Nerves in the area of the contact

point may be damaged. Muscle contractions may cause bone fractures from either the contractions themselves or from

falls.

• Higher voltages can cause larger currents and more severe shocks.

A severe shock can cause much more damage to the body than is visible. A person may suffer internal bleeding and

destruction of tissues, nerves, and muscles. Sometimes the hidden injuries caused by electrical shock result in a delayed

death. Shock is often only the beginning of a chain of events. Even if the electrical current is too small to cause injury,

your reaction to the shock may cause you to fall, resulting in bruises, broken bones, or even death.

• Some injuries from electrical shock cannot be seen.

The length of time of the shock greatly affects the amount of injury. If the shock is short in duration, it may only be

painful. A longer shock ( lasting a few seconds) could be fatal if the level of current is high enough to cause the heart to go

into ventricular fibrillation. This is not much current when you realize that a small power drill uses 30 times as much cur-rent

as what will kill. At relatively high currents, death is certain if the shock is long enough. However, if the shock is

short and the heart has not been damaged, a normal heartbeat may resume if contact with the electrical current is eliminat-ed.

( This type of recovery is rare.)

• The greater the current, the greater the shock.

• Severity of shock depends on voltage, amperage, and resistance.

• Resistance— a material’s ability to decrease or stop electrical current.

• Ohm— unit of measurement for electrical resistance.

• Lower resistance causes greater currents.

• Currents across the chest are very dangerous.

The amount of current passing through the body also affects the severity of an electrical shock. Greater voltages pro-duce

greater currents. There is greater danger from higher voltages. Resistance hinders current. The lower the resistance

( or impedance in AC circuits), the greater the current will be. Dry skin may have a resistance of 100,000 ohms or more.

Wet skin may have a resistance of only 1,000 ohms. Wet working conditions or broken skin will drastically reduce resis-tance.

The low resistance of wet skin allows current to pass into the body more easily and give a greater shock. When

more force is applied to the contact point or when the contact area is larger, the resistance is lower, causing stronger

shocks.

The path of the electrical current through the

body affects the severity of the shock. Currents

through the heart or nervous system are most

dangerous. If you contact a live wire with your

head, your nervous system will be damaged.

Contacting a live electrical part with one hand-while

you are grounded at the other side of

your body- will cause electrical current to pass

across your chest, possibly injuring your heart

and lungs.

• NEC— National Electrical Code— a com-prehensive

listing of practices to protect

workers and equipment from electrical

hazards such as fire and electrocution

There have been cases where an arm or leg

is severely burned by high- voltage electrical

9

Power drills use 30 times as much

current as what will kill.

current to the point of coming off, and the victim is not electrocuted. In these cases, the current passes through only a part

of the limb before it goes out of the body and into another conductor. Therefore, the current does not go through the chest

area and may not cause death, even though the victim is severely disfigured. If the current does go through the chest, the

person will almost surely be electrocuted. A large number of serious electrical injuries involve current passing from the

hands to the feet. Such a path involves both the heart and lungs. This type of shock is often fatal.

Summary

The danger from electrical shock depends on

• The amount of the shocking current through the body.

• The duration of the shocking current through the body.

• The path of the shocking current through the body.

10

3

Arc Flash/ NFPA 70E

OSHA revised Subpart S to reflect updated industry practices and technology and to incorporate the 2000 edition of

NFPA 70E, Electrical Safety Requirements for Employee Workplaces, and the 2002 revision of the National Electric

Code ( NEC). NFPA 70E applies to all personnel working on energized equipment greater than 50 volts or equipment that

could produce an arc flash, which means virtually every industry has employees at risk. Under the newly revised Subpart

S— Electrical ( effective Aug. 13, 2007), OSHA as well as NCDOL has not adopted NFPA 70E in its entirety, specifically

excluding some personal protective equipment and clothing requirements in regard to arc flash.

What Is an Arc Flash?

The arc flash is the resulting discharge of energy caused by an arcing fault. An arcing fault is the unintended flow of

current through a medium not intended to carry the current. That just means that the electricity is flowing through some-thing

it should not be; in most cases that result in injury, the medium was the air. The air becomes like a piece of copper,

conducting the electricity; only with the air, you can see the massive discharge of the electrons from the discharging ele-ment.

This is the arc flash. It is lightning on a smaller, yet still deadly, scale.

What causes an arcing fault? The most common causes of an arcing fault are equipment failure, human error ( improper

placement of tools or improper use of equipment), or the conduction of electricity due to foreign particles in the air ( usu-ally

metal shavings). 4

Wearing personal protective equipment is necessary in reducing injury from electrical arc flash accidents, but it is no

substitute for proper safety training, among other best practices in arc safety.

Every day, electrical arc flash accidents injure or kill, but wearing proper personal protective equipment ( PPE) mini-mizes

accident frequency and severity. PPE alone, however, is no substitute for thorough safety training, consistently

following lockout/ tagout procedures, keeping electrical equipment well- maintained, and applying engineering controls.

Burns are not the only risk. A high- amperage arc produces an explosive pressure wave blast that can cause severe fall-related

injuries.

Four- step hazard calculations: First, establish the job’s hazard risk category. Second, determine what clothing and

equipment the hazard risk category requires. Third, identify what arc thermal performance value ( ATPV) rating is neces-sary.

Finally, select personal protective equipment that meets or exceeds the designated ATPV rating.

Arc Flash Clothing

Arc flash clothes are critically important to keep workers safe. Statistics show that five to ten times a day, a worker in

the United States is injured or killed due to an arc flashing accident. 5 The casualties resulting from these accidents are

almost always devastating to the worker involved and to the worker’s family. 5 Perhaps if these workers had been wearing

appropriately rated arc flashing protective equipment, the number of injuries and deaths could have been decreased.

Need for Protective Clothing

What steps can be taken to reduce the risk? NFPA 70E, Standard for Electrical Safety Requirements for Employee

Workplaces, sets standards and regulations for workers working around energized equipment. NFPA 70E defines neces-sary

steps to be taken to properly prevent serious injury in the event of an arc flash accident. NFPA 70E interprets that

workers within the flash protection boundary ( the area where discharged energy is greater than 1.2 cal/ cm2) must be

qualified and wearing thermally resistant and arc flash protective clothing.

11

____________

4 http:// www. lg. com/ about/ newsletter/ June04/ ArcFlash. html

5 http:// www. carolinaseca. org/ pdf/ arcflash. pdf

Arc Flash Clothing Selection

Picking the right type of arc flash protective clothing is easy. First, consult NFPA 70E, 2004 Edition, Table

130.7( C)( 9)( a), to determine to which category of risk a particular activity belongs. Second, consult Table 130.7( C)( 10) to

determine what type of clothing/ equipment is required based on the category of risk determined. Third, consult Table

130.7( C)( 11) to determine the ATPV ( arc thermal performance value) rating needed. Once you have done all this, just go

out and find the protective gear that meets or exceeds this rating. 6 One thing to remember when picking the protective

work wear is to try and ensure that no skin is exposed. Ensure that the pant legs ( if not connected to boots) completely go

down to the boot. Also ensure that the sleeves of the protective work wear go down to the hand, leaving none of the arm

exposed. And lastly, remember that the head is the most vulnerable part of the body. Do not forget to complete the arc

flash protective clothing with suitable head gear of the same ATPV rating as the rest of the work- wear plus high voltage

gloves.

NFPA 70E Table 130.7( C)( 11)

Protective Clothing Characteristics6

When nothing can be done about working within a flash protection boundary, proper arc flash protective clothing needs

to be worn. Workers need to remember that arc flash accidents do not only occur with equipment at high voltage. The

majority of arc flash accidents occur with low ( 120V) and medium voltage ( 480V) equipment. Workers who wear the

proper arc flash protective clothing will significantly reduce the risk of injury or death should an arc flash accident occur.

Summary

Always perform a flash hazard analysis and acquire the appropriate flash retardant clothing ( FRC). Care and

laundering of FRC should be taken cautiously. Employer/ employees must follow safe work practices. Employees must be

adequately trained on electrical safety, with first aid/ CPR training as needed. Whenever possible, lock out all equipment!

12

Hazard Risk Work- wear Description ATPV

Category ( 1/ 2/ 3/ 4) refers to the number of clothing layers Rating cal/ cm2

0 Untreated Cotton ( 1) n/ a

1 FR Shirt and FR Pant ( 1) 5

2 Cotton Undergarments + FR Shirt/ Pant ( 2) 8

3 Cotton Undergarments + FR Shirt/ Pant + FR Coveralls ( 3) 25

4 Cotton Undergarments + FR Shirt/ Pant + Double Layer Switching Coat

and Pant ( 4) 40

* Recommendation is 100 percent cotton.

____________

6 http:// www. labsafety. com/ refinfo/ printpage. htm? page=/ refinfo/ ezfacts/ ezf263. htm

4

Branch Circuit Wiring

Definitions

Discussion of wiring methods must be preceded by an understanding of terms used to define each specific conductor in

a typical 120/ 240 volt AC system. Refer to Figure 4 for an example of most of the following definitions. The National

Electrical Code ( NEC) is used as the reference source.

Ampacity. The current ( in amps) that a conductor can carry continuously under the conditions of use without exceed-ing

its temperature rating. When you find attachment plugs, cords or receptacle face plates that are hot to touch, this may

be an indication that too much of a load ( in amps) is being placed on that branch circuit. If the insulation on the conduc-tors

gets too hot, it can melt and cause arcing, which could start a fire.

Attachment Plug. Describes the device ( plug) that when inserted into the receptacle establishes the electrical connec-tion

between the appliance and branch circuit.

Branch Circuit. The electrical conductors between the final overcurrent device ( the service entrance panel ( SEP) in

Figure 4) protecting the circuit and the receptacle. The wiring from the SEP to the pole mounted transformer is called the

“ service.”

Circuit Breaker. Opens and closes a circuit by nonautomatic means as well as being designed to open automatically at

a predetermined current without causing damage to itself. Be alert to hot spots in circuit breaker panels indicating that the

circuit breaker is being overloaded or that there may be loose connections.

Equipment. A general term for material, fittings, devices, appliances, fixtures, apparatus and the like used as a part of,

or in connection with, an electrical installation. In Figure 4, the SEP and any associated conduit and junction boxes would

be considered equipment.

Feeder. The term given to the circuit conductors between the SEP and the final branch circuit overcurrent device. In

Figure 4 there is no feeder since the SEP is also the final branch circuit overcurrent device.

Ground. A conducting connection ( whether intentional or accidental) between an electrical circuit or equipment and

the earth, or to some conducting body that serves in place of the earth. It is important to remember that a conducting body

can be in the ceiling and that we must not

think of ground as restricted to earth. This

is why maintenance personnel may not

realize that a ground loop exists in the

space above a drop ceiling, due to the elec-trical

conduit and other grounded equip-ment

in that space.

Grounded Conductor. The conductor

in the branch circuit wiring that is inten-tionally

grounded in the SEP. This conduc-tor

is illustrated in Figure 4. From the SEP

to the transformer the same electrical path

is referred to as the neutral. From the final

overcurrent device to the receptacle the

conductor is referred to as the grounded

conductor.

13

120 Volts

120 Volts

Neutral

Grounding Electrode

Conductor on

Premises

Equipment- grounding

Conductor ( green or bare)

Utility

Supply

Service

Ground

Circuit Breaker

Grounded

Conductor

( white or gray)

“ Hot” Conductor

( black or red)

Typical Pole

Transformer

Service

Entrance

Panel

Nickel or

Light- colored

Terminal

Green

Hexagonal- head

Terminal Screw

Brass colored

Terminal

Primary Lines

2.4– 13 kV

Figure 4

Branch Circuit Wiring

Grounding Conductor, Equipment. The conductor used to connect the noncurrent- carrying metal parts of equipment,

raceways and other enclosures to the system grounded conductor at the SEP. The equipment grounding conductor path is

allowed to be a separate conductor ( insulated or noninsulated), or where metal conduit is used, the conduit can be used as

the conductor. There are some exceptions to this such as in hospital operating and intensive care rooms. The equipment

grounding conductor is the human safety conductor of the electrical system in that it bonds all noncurrent- carrying metal

surfaces together and then connects them to ground. By doing this we can prevent a voltage potential difference between

the metal cabinets and enclosures of equipment and machinery. This conductor also acts as a low impedance path ( in the

event of a voltage fault to the equipment case or housing) so that if high fault current is developed, the circuit breaker or

fuse will be activated quickly.

Grounding Electrode Conductor. Used to connect the grounding electrode to the equipment grounding conductor

and/ or to the grounded conductor of the circuit at the service equipment or at the source of a

separately derived system ( see Figure 4).

Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor is considered

overcurrent. This condition may result from an overload, short circuit or a ground fault.

Wiring Methods

The NEC requires the design and installation of electrical wiring to be consistent throughout the facility. To accomplish

this, it is necessary to follow NEC requirements. For 120 volt grounding- type receptacles, the following wiring connec-tions

are required ( see Figure 4).

• The ungrounded or “ hot” conductor ( usually with black or red insulation) is connected to the brass colored terminal

screw. This terminal and the metal tension springs form the small slot receiver for any appliance attachment plug.

An easy way to remember the color coding is to remember “ black to brass” or the initials “ B & B.”

• The “ grounded conductor” insulation is generally colored white ( or gray) and should be fastened to the silver or light

colored terminal. This terminal and the metal tension springs form the large slot for a polarized attachment plug. An

easy way to remember this connection is to think “ white to light.”

• The equipment grounding conductor path can be a conductor, or where metal conduit is used, the conduit can be sub-stituted

for the conductor. If the latter is used, you must monitor the condition of the conduit system to ensure that it

is not damaged or broken. Any “ open” in the conduit system will eliminate the equipment grounding conductor

path. Additionally, the condition of the receptacles must be monitored to ensure that they are securely fastened to

the receptacle boxes. When a third wire is run to the receptacle either in a conduit or as a part of a nonmetallic

sheathed cable assembly, the conductor must be connected to the green colored terminal on the receptacle.

These wiring methods must be used to ensure that the facility is correctly wired. Circuit testing methods will be dis-cussed

in Part 5. In older homes, knob and tube or other two- wire systems may be present. The NEC requires that ground-ing

type receptacles be used as replacements for existing nongrounding types and be connected to a grounding conductor.

An exception is that where a grounding means does not exist in the enclosure, either a nongrounding or a GFCI- type

receptacle must be used. A grounding conductor must not be connected from the GFCI receptacle to any outlet supplied

from the GFCI receptacle. The exception further allows nongrounding type receptacles to be replaced with the grounding

type where supplied through a GFCI receptacle.

Plug and Receptacle Configurations

Attachment plugs are devices that are fastened to the end of a cord so that electrical contact can be made between the

conductor in the equipment cord and the conductors in the receptacle. The plugs and receptacles are designed for different

voltages and currents, so that only matching plugs will fit into the correct receptacle. In this way, a piece of equipment

rated for one voltage and/ or current combination cannot be plugged into a power system that is of a different voltage or

current capacity.

The polarized three- prong plug is designed with the equipment grounding prong slightly longer than the two parallel

blades. This provides equipment grounding before the equipment is energized. Conversely, when the plug is removed

from the receptacle, the equipment grounding prong is the last to leave, ensuring a grounded case until power is removed.

The parallel line blades maybe the same width on some appliances since the three- prong plug can only be inserted in one

14

way. A serious problem results whenever a person breaks or cuts off the grounding prong. This not only voids the safety

of the equipment grounding conductor but allows the attachment plug to be plugged in with the correct polarity or with

the wrong polarity.

Figure 5 illustrates some of the

National Electrical Manufacturers

Association ( NEMA) standard plug and

receptacle connector blade configura-tions.

Each configuration has been devel-oped

to standardize the use of plugs and

receptacles for different voltages,

amperes, and phases from 115 through

600 volts and from 10 through 60 amps,

and for single- and three- phase systems.

You should be alert to jury- rigged

adaptors used to match, as an example, a

50 amp attachment plug to a 20 amp

receptacle configuration. Using these

adaptors poses the danger of mixing volt-age

and current ratings and causing fire

and/ or shock hazards to personnel using

equipment. Equipment attachment plugs

and receptacles should match in voltage

and current ratings to provide safe power

to meet the equipment ratings. Also the

attachment plug cord clamps must be

secured to the cord to prevent any strain

or tension from being transmitted to the ter-minals

and connections inside the plug.

Understanding Reverse Polarity

The NEC recognizes the problem of reverse polarity. It states that no grounded conductor may be attached to any ter-minal

or lead so as to reverse the designated polarity. Many individuals experienced with electrical wiring and appliances

think that reverse polarity is not hazardous. A few example situations should heighten your awareness of the potential

shock hazard from reverse polarity.

An example of one hazardous situation

would be an electric hand lamp. Figure 6

illustrates a hand lamp improperly wired and

powered.

When the switch is turned off, the shell of

the lamp socket is energized. If a person acci-dentally

touched the shell ( while changing a

bulb) with one hand and encountered a

ground loop back to the transformer, a shock

could result. If the lamp had no switch and

was plugged in as shown, the lamp shell

would be energized when the plug was insert-ed

into the receptacle. Many two- prong plugs

have blades that are the same size, and the

right or wrong polarity is just a matter of

chance. If the plug is reversed ( Figure 7), the

voltage is applied to the bulb center terminal

15

Only

5- 15R 5- 15P

5- 20R 5- 20P

10- 50R 10- 50P

10- 30R 10- 30P

6- 30R 6- 30P

125/ 250- Volt, 30- Ampere

Receptacle and Plug

250- Volt, 30- Ampere

Receptacle and Plug

125/ 250- Volt, 50- Ampere

Receptacle and Plug

20- Ampere Plug,

125- Volt Receptacles

and Plugs

Either

15- Ampere Plug

15 Ampere

20 Ampere

W

X Y

W

Y X

W

Y X

W

X Y

W

G

W

G

W

G

W

G

G G

Figure 5

Plug and Receptacle Configurations

Switch

OFF Position

Bulb

Metal Guard

Ground Potential

Equipment Plug

Receptacle

“ Hot”

“ Hot”

SEP

120 Volt

Transformer

Figure 6

Hand Lamp— Reverse Polarity

and the shell is at ground potential. Contact

with the shell and ground would not create a

shock hazard in this situation. In this example

the hand lamp is wired correctly.

Another example is provided by electric

hair dryers or other plastic- covered electrical

appliances. Figure 8 illustrates a hair dryer

properly plugged into a receptacle with the

correct polarity.

You will notice that the switch is single

pole- single throw ( SPST). When the appli-ance

is plugged in with the switch in the hot

or 120 volt leg, the voltage stops at the switch

when it is in the off position. If the hair dryer

were accidentally dropped into water, current could flow out of the plastic housing, using the water as the conducting

medium. The water does not short out the appliance since the exposed surface area of the hot wire connection to the

switch terminal offers such a high resis-tance.

This limits the current flow to less

than 1 mA ( correct polarity). The fault

current is not sufficient to trip a 20- amp

circuit breaker. To trip the circuit break-er,

there would have to be a line- to- line

short that would cause an excess of 20

amps ( 20,000 mA). Should a person try

to retrieve the appliance from the water

while it is still plugged into the outlet?

In this configuration, the fault current

would be extremely low ( unless the

switch were in the on position). Since

you have no way to tell if the polarity is

correct, don’t take chances. NEVER

REACH INTO WATER TO RETRIEVE

AN APPLIANCE. Always unplug the appliance first, then retrieve the appliance and dry it out.

If the appliance is plugged in as shown in Figure 9, when the switch is off, voltage will be present throughout all the

internal wiring of the appliance. Now if it is dropped into water, the drastically increased “ live” surface area will allow a

drastic increase in the available electric current ( I = E/ R). A person who accidentally tries to retrieve the dryer would be in

a hazardous position because the voltage in the water could cause current to flow through the body ( if another part of the

body contacts a ground loop). This illus-trates

the concept that reverse polarity is a

problem whenever appliances are used

with plastic housings in areas near sinks,

or where the appliance is exposed to rain

or water. Remember, most motorized

appliances have air passages for cooling.

Wherever air can go, so can moisture and

water.

If the appliance had a double pole- dou-ble

throw switch ( DPDT), it would make

no difference how the plug was positioned

in the outlet. The hazard would be mini-mized

since the energized contact surface

would be extremely small. If the appliance

16

Switch

OFF Position

Bulb

Metal Guard

Ground Potential

Equipment Plug

Receptacle

“ Hot”

“ Hot”

“ Hot”

SEP

120 Volt

Transformer

Figure 7

Hand Lamp— Correct Polarity

Service

Entry

Panel

( SEP)

120 Volt

Transformer

Plug

Receptacle

“ Hot”

“ Hot”

Hair Dryer

Switch

Figure 8

Hair Dryer— Correct Polarity

Service

Entry

Panel

( SEP)

120 Volt

Transformer

Plug

Receptacle

“ Hot”

“ Hot”

Hair Dryer

Switch

Figure 9

Hair Dryer— Reverse Polarity

were dropped into water, a high resistance contact in the water and a resulting low available fault current ( I = E/ R) would

result. Later, we will see how GFCIs can be used to protect against shock hazards when using appliances with noncon-ductive

housings around water.

Remember that any electric appliance dropped in water or accidentally exposed to moisture should be considered as ener-gized.

The electric power must be safely removed from the appliance before it is retrieved or picked up. You never know if

the appliance is plugged in with the right polarity without test equipment. Do not take chances. Remove the power first.

Grounding Concepts

Grounding falls into two safety categories. It is important to distinguish between “ system grounding” and “ equipment

grounding.” Figure 10 illustrates these two grounding components. The difference between these two terms is that system

grounding actually connects one of the current carrying conductors from the supply transformer to ground. Equipment

grounding connects or bonds all of the noncurrent- carrying metal surfaces together and then is connected to ground.

System grounding ( Figure 10) at the transformer provides a grounding point for the power company surge and light-ning

protection devices. In conjunction with the system grounding at the SEP, the voltage across system components is

limited to a safe value should they be subject-ed

to lightning or high voltage surges. The

system grounding at the SEP also helps to

limit high voltages from entering the electri-cal

system beyond the SEP. It is important to

check all of the connections both indoors and

outdoors since many times they are exposed

to moisture, chemicals and physical damage.

Equipment grounding does two things.

First, it bonds all noncurrent- carrying metal

surfaces together so that there will be no

potential difference between them. Second, it

provides a path for current to flow under

ground fault conditions. The equipment

grounding path must have low impedance to

ensure rapid operation of the circuit overcur-rent

device should a “ hot” to ground fault

occur.

Figure 11 depicts some common equip-ment

faults that can occur. A problem with

the equipment grounding system is that under

normal conditions it is not a current- carrying

conductor and a fault would not be readily

detected. Necessary visual inspection will not

provide an operational verification. In Figure

11 we can test the condition of the equipment

grounding conductor using test procedures in

this guide. To test the quality of the branch

circuit equipment grounding system, a special

tester called a ground loop impedance tester

is needed. It is generally recommended that

an impedance of 0.5 ohms be achieved in the

equipment grounding conductor path. In case

of a “ hot” to ground fault, the fault current

would quickly rise to a value ( I = E/ R =

120/ 0.5 = 240 amps) necessary to trip a 20

amp fuse or breaker.

17

Equipment Grounding

Equipment

Grounding

Conductor

Electrical Symbol

For Ground

Service

Entrance

Grounded

Conductor or

Neutral

Transformer

Secondary

Primary

Most Metallic Raceways, Cable Sheaths

and Cable Armor That Are Continuous

and Utilize Proper Fittings May Serve as

the Equipment Grounding Conductor. A

Separate Grounding Conductor is Needed

When Plastic Conduit, Non- metallic

Sheathed Cable or Other Wiring Methods

Are Used That Are Not Approved as

Grounding Methods.

Figure 10

System and Equipment Grounding

? ? Fault

White

Black

Receptacle Ground

Fault

Tool or

Appliance

Grounding Prong

Missing

Ground Fault

Current

Wire or

Conduit

Service

Entrance

Source

Figure 11

Equipment Grounding Faults

If there is an open or break in the conduit system, as shown in Figure 11, a fault in a power tool with a good grounding

prong would allow the voltage to be placed directly on the ungrounded conduit. This would create a serious shock hazard

to anyone touching the conduit with one hand while touching a ground loop with the other. The missing ground prong

( with a good conduit or equipment grounding path) would create a serious shock hazard to the person if the ground loop

through the feet was low resistance ( e. g., wet earth or concrete and wet shoes). It is important to emphasize the need for

low impedance on the equipment grounding loop. If the ground fault current loop in Figure 11 were 25 ohms and the

body resistance of the person were 850 ohms, then the 25 ohm ground loop resistance would be too high to cause enough

circuit breaker current to trip it open. In this case, the person would then receive multiples of current considered deadly

( 141 mA in this case) through the body, causing death in most instances. Remember that standard circuit breakers are for

equipment and fire protection, not people protection. However, ground fault circuit interrupter ( GFCI) circuit breakers are

specifically designed for people protection.

Burns Caused by Electricity

The most common shock- related, nonfatal injury is a burn. Burns caused by electricity may be of three types: electrical

burns, arc burns and thermal contact burns. Electrical burns can result when a person touches electrical wiring or

equipment that is used or maintained improperly. Typically such burns occur on the hands. Electrical burns are one of the

most serious injuries you can receive. They need to be given immediate attention. Additionally, clothing may catch fire and

a thermal burn may result from the heat of the fire.

• Electrical shocks cause burns.

Arc- blasts occur when powerful, high- amperage currents arc through the air. Arcing is the luminous electrical dis-charge

that occurs when high voltages exist across a gap between conductors and current travels through the air. This situ-ation

is often caused by equipment failure due to abuse or fatigue. Temperatures as high as 35,000 F have been reached in

arc- blasts.

• arc- blast— explosive release of molten material from equipment caused by high- amperage arcs

• arcing— the luminous electrical discharge ( bright, electrical sparking) through the air that occurs when high volt-ages

exist across a gap between conductors

There are three primary hazards associated with an arc- blast.

1. Arcing gives off thermal radiation ( heat) and intense light, which can cause burns. Several factors affect the degree

of injury, including skin color, area of skin exposed and type of clothing worn. Proper clothing, work distances and

overcurrent protection can reduce the risk of such a burn.

2. A high- voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000- amp arc

feels a force of about 480 pounds on the front of the body. In addition, such an explosion can cause serious ear

damage and memory loss due to concussion. Sometimes the pressure wave throws the victim away from the arc-blast.

While this may reduce further exposure to the thermal energy, serious physical injury may result. The pres-sure

wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap

off the heads of steel bolts and knock over walls.

3. A high- voltage arc can also cause many of the copper and aluminum components in electrical equipment to melt.

These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden

rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are

10 feet or more away.

18

Electrical Fires

Electricity is one of the most common causes of fires and thermal burns in homes and workplaces. Defective or mis-used

electrical equipment is a major cause of electrical fires. If there is a small electrical fire, be sure to use only a Class

C or multi- purpose ( ABC) fire extinguisher, or you might make the problem worse. All fire extinguishers are marked with

letter( s) that tell you the kinds of fires they can put out. Some extinguishers contain symbols, too. The letters and symbols

are explained below ( including suggestions on how to remember them).

A( think: Ashes) = paper, wood, etc.

B( think: Barrel) = flammable liquids

C( think: Circuits) = electrical fires

Here are a couple of fire extinguishers at a worksite. Can you tell what types of

fires they will put out?

19

Five technicians were performing preventive maintenance on the electrical system of a railroad maintenance facility.

One of the technicians was assigned to clean the lower compartment of an electrical cabinet using cleaning fluid in

an aerosol can. He began to clean the upper compartment as well. The upper compartment was filled with live cir-cuitry.

When the cleaning spray contacted the live circuitry, a conductive path for the current was created. The cur-rent

passed through the stream of fluid, into the technician’s arm and across his chest. The current caused a loud

explosion. Co- workers found the victim with his clothes on fire. One worker put out the fire with an extinguisher, and

another pulled the victim away from the compartment with a plastic vacuum cleaner hose. The paramedics

responded in 5 minutes. Although the victim survived the shock, he died 24 hours later of burns.

This death could have been prevented if the following precautions had been taken:

• Before doing any electrical work, de- energize all circuits and equipment, perform lockout/ tagout, and test circuits

and equipment to make sure they are de- energized.

• The company should have trained the workers to perform their jobs safely.

• Proper personal protective equipment ( PPE) should always be used.

• Never use aerosol spray cans around high- voltage equipment.

This extinguisher can only be used on Class B

and Class C fires.

This extinguisher can only be used on

Class A and Class C fires.

Thermal burns may result if an explosion occurs when electricity ignites an explosive mixture of material in the air.

This ignition can result from the buildup of combustible vapors, gases or dusts. OSHA standards, the NEC and other safe-ty

standards give precise safety requirements for the operation of electrical systems and equipment in such dangerous

areas. Ignition can also be caused by overheated conductors or equipment, or by normal arcing at switch contacts or in

circuit breakers.

Summary

Burns are the most common injury caused by electricity. The three types of burns are electrical burns, arc burns and

thermal contact burns.

20

Note: However, do not try to put out fires unless you have

received proper training. If you are not trained, the best thing

you can do is evacuate the area and call for help.

5

Branch Circuit and Equipment Testing

Testing Branch Circuit Wiring

Branch circuit receptacles should be tested periodically. The frequency of testing should be established on the basis of

outlet usage. In shop areas, quarterly testing may be necessary. Office areas may only need annual testing. A preventive

maintenance program should be established. It is not unusual to find outlets as old as the facility. For some reason, a pop-ular

belief exists that outlets never wear out. This is false. For example, outlets take severe abuse from employees discon-necting

the plug from the outlet by yanking on the cord. This can put severe strain on the contacts inside the outlet as well

as on the plastic face.

The electrical receptacle is a critical electrical system component. It must provide a secure mechanical connection for

the appliance plug so that there is a continuous electrical circuit for each of the prongs. Receptacles must be wired correct-ly,

or serious injuries can result from their use. For this reason, the following two- step testing procedure is recommended.

Receptacle Testing

Step 1

Plug in a three- prong receptacle circuit tester and note the combination of the

indicator lights ( see Figure 12). The tester checks the receptacle for the proper con-nection

of the grounding conductor, wiring polarity and other combinations of

wiring errors. If the tester checks the receptacle as OK, proceed to the next step. If

the tester indicates a wiring problem, have it corrected as soon as possible. Retest

after the problem is corrected.

Step 2

After the outlet has been found to be

wired ( electrically) correct, the receptacle

contact tension test must be made. A typical tension tester is shown in Figure 13.

The tension should be 8 ounces or more. If it is less than 8 ounces, have it

replaced. The first receptacle function that loses its contact tension is usually the

grounding contact circuit. The plug grounding prong is the last part to leave the

receptacle. Because of the leverage ( due to its length) it wears out the tension of

the receptacle contacts quicker than the parallel blade contacts. Since this is the

human safety portion of the grounding system, it is very important that this contact

tension be proper. In determining the frequency of testing, the interval must be

based on receptacle usage. All electrical maintenance personnel should be

equipped with receptacle circuit and tension testers. Other maintenance employees could also be equipped with testers

and taught how to use them. In this manner, the receptacles can be tested before maintenance workers use them. Home

receptacles should also be tested.

Testing Extension Cords

New extension cords should be tested before being put into service. Many inspectors have found that new extension

cords have open ground or reverse polarity. Do not assume that a new extension cord is correct. Test it.

Extension cord testing and maintenance are extremely important. The extension cord takes the electrical energy from a

fixed outlet or source and provides this energy at a remote location. The extension cord must be wired correctly, or it can

become the critical fault path.

Testing of extension cords new and used should use the same two steps as used in electrical outlet testing. These two

steps are:

21

Figure 12

Receptacle Tester

Figure 13

Receptacle Tension Tester

Step 1

Plug the extension cord into an electrical outlet that has successfully passed the outlet testing procedure. Plug in any

three- prong receptacle circuit tester into the extension receptacle and note the combination of indicator lights. If the tester

checks the extension cord as OK, proceed to the next step. If the tester indicates a faulty condition, repair or replace the

cord. Once the extension cord is correctly repaired and passes the three- prong circuit tester test, proceed to step 2.

Step 2

Plug a reliable tension tester into the receptacle end. The parallel receptacle contact tension and the grounding contact

tension should check out at 8 ounces or more. If the tension is less than 8 ounces, the receptacle end of the extension cord

must be repaired. As with fixed electrical outlets, the receptacle end of an extension cord loses its grounding contact ten-sion

first. This path is the critical human protection path and must be both electrically and mechanically in good condition.

Testing Plug- and Cord- Connected Equipment

The last element of the systems test is the testing of plug- and cord- connected equipment. The electrical inspector

should be on the alert for jury- rigged repairs made on power tools and appliances. Many times a visual inspection will

disclose three- prong plugs with the grounding prong broken or cut off. In such instances, the grounding path to the equip-ment

case has been destroyed. ( The plug can now also be plugged into the outlet in the reverse polarity configuration.)

Double insulated equipment generally has a nonconductive case and will not be tested using the procedures discussed

below. Some manufacturers that have listed double insulation ratings may also provide the three- prong plug to ground

any exposed noncurrent- carrying metal parts. In these cases, the grounding path continuity can be tested.

A common error from a maintenance standpoint is the installation of a three- prong plug on a two- conductor cord to the

appliance. Obviously, there will be no grounding path if there are only two conductors in the cord. Some hospital grade

plugs have transparent bases that allow visual inspection of the electrical connection to each prong. Even in that situation,

you should still perform an electrical continuity test.

Maintenance shops may have commercial power tool testing equipment. Many power tool testers require the availabili-ty

of electric power. The ohmmeter can be used in the field and in locations where electric power is not available or is not

easily obtained. Plug- and cord- connected equipment tests are made on de- energized equipment. Testing of de- energized

equipment in wet and damp locations can also be done safely.

The plug- and cord- connected equipment test using a self- contained battery- powered ohmmeter is simple and straight-forward.

The two- step testing sequence that can be performed on three- prong plug grounded equipment follows:

Step 1— Continuity Test— Ground Pin to Case Test

Set the ohmmeter selector switch to the lowest scale

( such as R X 1). Zero the meter by touching the two test

probes together and adjusting the meter indicator to zero.

Place one test lead ( tester probe) on the grounding pin of

the de- energized equipment as shown in Figure 14. While

holding that test lead steady, take the other test lead and

make contact with an unpainted surface on the metal case

of the appliance. You should get a reading of less than 1

ohm. If the grounding path is open, the meter will indicate

infinity. If there is no continuity, then the appliance must

be tagged out and removed from service. If the appliance

grounding path is OK, proceed to step 2.

22

White

MOTOR

Green

Silver

Brass

Black

Metal Case

Tester Probe

Tester Probe

SPST

Switch

R X 1

Scale

Reading 1 ohm

or less

Figure 14

Continuity Test

Step 2— Leakage Test— Appliance Leakage Test

Place the ohmmeter selector switch on the highest ohm test position ( such as R X 1,000). Set the meter at zero. Place

one test lead on an unpainted surface of the appliance case ( see Figure 15), then place the other test lead on one of the

plug’s parallel blades.

Observe the reading. The ideal is close to infinity. ( If

a reading of less than 1 meg- ohm is noted, return the

appliance to maintenance for further testing.) With one

test lead still on the case, place the other test lead on

the remaining parallel blade and note the ohmmeter

reading. A reading approaching infinity is required.

( Again, anything less than 1 meg- ohm should be

checked by a maintenance shop.)

23

White

MOTOR

Green

Silver

1.

2.

Brass

Black

Metal Case

Tester Probe

Tester Probe

SPST

Switch

R X 1,000

Scale

Reading

8

Figure 15

Leakage Test

6

Voltage Detector Testing

Operation

When you are conducting an electrical inspection, a voltage detector should be used in conjunction with the circuit

tester, ohmmeter and tension tester. Several types of these devices are inexpensive and commercially available.

These testers are battery powered and are constructed of nonconduct-ing

plastic. Lightweight and self- contained, these testers make an ideal

inspection tool.

The voltage detector works like a radio receiver in that it can receive

or detect the 60 hertz electromagnetic signal from the voltage waveform

surrounding an ungrounded (“ hot”) conductor. Figure 17 illustrates the

detector being used to detect the “ hot” conductor in a cord connected to

a portable hand lamp. When the front of the detector is placed near an

energized “ hot” or ungrounded conductor, the tester will provide an

audible as well as a visual warning. In Figure 17 if the plug were dis-connected

from the receptacle, the detector would not sound an alarm

since there would not be any voltage waveform present.

Typical Voltage Detector Uses

The detector can also be used to test for properly

grounded equipment. When the tester is positioned on a

properly grounded power tool ( e. g., the electric drill in

Figure 18), the tester will not sound a warning. The rea-son

is that the electromagnetic field is shielded from the

detector so that no signal is picked up. If the grounding

prong had been removed and the drill were not ground-ed,

the electromagnetic waveform would radiate from

the drill and the detector would receive the signal and

give off an alarm.

As illustrated in Figure 18, the detector can be used

to test for many things during an inspection.

Receptacles can be checked for proper AC polarity.

Circuit breakers can be checked to determine if they are

on or off. All fixed equipment can be checked for prop-er

grounding. If the detector gives a warning indication

on any equipment enclosed by metal, perform further

testing with a volt- ohmmeter. Ungrounded equipment

can be ungrounded or, in addition, there may be a fault

to the enclosure making it “ hot” with respect to ground.

An experienced inspector should use the voltmeter to

determine if there is voltage on the enclosure. The volt-age

detector should be used as an indicating tester and

qualitative testing should be accomplished with other

testing devices such as a volt- ohmmeter. The use of the

detector can speed up the inspection process by allow-ing

you to check equipment grounding quickly and

safely.

24

Switch

Audible Alarm

Test Marker

“ Red” Warning Light

“ Green” Power “ On” Light

Figure 16

Voltage Detector

SEP

“ Hot”

“ Hot”

120 Volt

Receptacle

Transformer

Figure 17

Testing for “ Hot” Conductor

Check Fixed

Equipment

Grounding

Easily Check

Power Tools for

Proper Grounding

Safely and Quickly

Check for

Voltage

at AC Outlets

Quickly

Check

Circuit

Breakers

Figure 18

Typical Voltage Detector Uses

Voltage Versus Detection Distance

Another unique feature of the voltage detector shown in Figure 18 is that it is voltage sensitive. Figure 19 lists dis-tances

versus voltage at which the detector “ red” light will turn on. As an example, a conductor energized with 120 volts

AC can be expected to be detected from 0 to 1 inch from the conductor.

The transformer secondary wiring on a furnace

automatic ignition system rated at 10,000 volts

can be expected to be detected from 6 to 7 feet

away. You can use this feature to assist in making

judgments regarding the degree of hazard and

urgency for obtaining corrective action.

When you are using the voltage detector, you

must understand how it operates to interpret its

warning light properly. If you apply the tester to

an energized power tool listed as double insulat-ed,

you will see the red warning light turn on. In

this situation, the voltage waveform is detected

because there is no metal enclosure to shield the

waveform. The same would occur if you were to

test in any of the typewriters used in offices. This does not mean that the plastic or nonmetallic enclosed equipment is

unsafe, only that it is energized and not a grounding type piece of equipment. The examples and explanation of the opera-tional

features should be understood fully. Using the detector provides the opportunity for finding many electrical hazards

that others may have overlooked.

25

To Determine Approximate Voltage:

Slowly approach the circuitry being tested with the front sensor of the

unit and observe the distance at which the red LED light glows along

with the “ beep” sound. Use the chart below to determine the approxi-mate

voltage in the circuitry.

VOLTAGE ( V) 100 200 600 1K 5K 9K

DISTANCE ( inch) 0– 1 1– 2 3– 5 15 5 ft 6– 7 ft up

These figures may vary due to conditions governing the testing, i. e.,

static created by your standing on grounded material, carpets, etc.

Figure 19

Voltage vs. Detection Distance

7

Ground Fault Circuit Interrupters

Operational Theory

The ground fault circuit interrupter ( GFCI) is a fast- acting device that monitors the current flow to a protected load. The

GFCI can sense any leakage of current when current returns to the supply transformer by any electrical loop other than

through the white ( grounded conductor) and the black ( hot) conductors. When any “ leakage current” of 5 mA or more is

sensed, the GFCI, in a fraction of a second, shuts off the current on both the “ hot” and grounded conductors, thereby interrupt-ing

the fault current to the appliance and the fault loop.

This is illustrated in Figure 20. As long as I1 is equal to I2 ( normal appliance operation with no ground fault leakage),

the GFCI switching system remains closed. If a fault occurs between the metal case of an appliance and the “ hot” conduc-tor,

fault current I3 will cause an imbalance ( 5 mA or greater for human protection) allowing the GFCI switching system

to open ( as illustrated) and the removal of power from both the white and the “ hot” conductors.

Another type of ground fault can occur

when a person comes in contact with a “ hot”

conductor directly or touches an appliance

with no ( or a faulty) equipment grounding

conductor. In this case I4 represents the fault

current loop back to the transformer. This

type of ground fault is generally the type that

individuals are exposed to.

The GFCI is intended to protect people. It

de- energizes a circuit, or portion thereof, in

approximately 1/ 40 of a second when the

ground fault current exceeds 5 mA. The

GFCI should not be confused with ground

fault protection ( GFP) devices that protect

equipment from damaging line- to- ground

fault currents. Protection provided by GFCIs

is independent of the condition of the equip-ment

grounding conductor. The GFCI can protect personnel even when the equipment grounding conductor is accidental-ly

damaged and rendered inoperative.

The NEC requires that grounding type receptacles be used as replacements for existing nongrounding types. Where a

grounding means does not exist in the receptacle enclosure, the NEC allows either a nongrounding or GFCI receptacle.

Nongrounding type receptacles are permitted to be replaced with grounding type receptacles when powered through a

GFCI.

Remember that a fuse or circuit breaker cannot provide “ hot” to ground loop protection at the 5 mA level. The fuse or

circuit breaker is designed to trip or open the circuit if a line to line or line to ground fault occurs that exceeds the circuit

protection device rating. For a 15 amp circuit breaker, a short in excess of 15 amps or 15,000 mA would be required. The

GFCI will trip if 0.005 amps or 5 mA start to flow through a ground fault in a circuit it is protecting. This small amount

( 5 mA), flowing for the extremely short time required to trip the GFCI, will not electrocute a person but will shock the

person in the magnitude previously noted.

Typical Types of GFCIs

GFCIs are available in several different types. Figure 21 illustrates three of the types available ( portable, circuit break-er

and receptacle).

26

“ Hot”

Supply

I 1

I 2

I 3

I 4

N. C.

Protected

Load

Equipment

Grounding

Conductor

Sensing and

Test Circuit

External

Ground

Fault

Internal

Equipment

Fault

Grounded

Conductor

Differential

Transformer GFCI Protection Device

Figure 20

Circuit Diagram for a GFCI

Circuit breakers can be purchased with the GFCI protection built in. These combination types have the advantage of

being secured in the circuit breaker panel to prevent unauthorized persons from having access to the GFCI. The receptacle

type GFCI is the most convenient in that it can be tested and/ or reset at the location where it is used. It can also be

installed so that if it is closest to the circuit breaker panel, it will provide GFCI protection to all receptacles on the load

side of the GFCI. The portable type can be carried in a maintenance person’s tool box for instant use at a work location

where the available AC power is not GFCI protected. Other versions of GFCIs are available including multiple outlet

boxes for use by several power tools and for outdoor applications. A new type is available that can be fastened to a per-son’s

belt and carried to the job location.

The difference between a regular electrical recep-tacle

and a GFCI receptacle is the presence of the

TEST and RESET buttons. The user should follow

the manufacturer’s instructions regarding the testing

of the GFCI. Some instructions recommend pushing

the TEST button and resetting it monthly. Defective

units should be replaced immediately.

Be aware that a GFCI will not protect the user

from line ( hot) to line ( grounded conductor) electri-cal

contact. If a person were standing on a surface

insulated from ground ( e. g., a dry, insulated floor

mat) while holding a faulty appliance with a “ hot”

case in one hand, then reached with the other hand to

unplug an appliance plug that had an exposed

grounded ( white) conductor, a line to line contact

would occur. The GFCI would not protect the person

( since there is no ground loop). To prevent this type

of accident from occurring, it is very important to have an ensured equipment grounding conductor inspection program in

addition to a GFCI program. GFCIs do not replace an ongoing electrical equipment inspection program. GFCIs

should be considered as additional protection against the most common form of electrical shock and electrocution: the

line (“ hot”) to ground fault.

GFCI Uses

GFCIs should be used in dairies, breweries, canneries, steam plants, construction sites, and inside metal tanks and boil-ers.

They should be used where workers are exposed to humid or wet conditions and may come in contact with ground or

grounded equipment. They should be used in any work environment that is or can become wet and in other areas that are

highly grounded.

Nuisance GFCI Tripping

When GFCIs are used in construction activities, the GFCI should be located as close as possible to the electrical equip-ment

it protects. Excessive lengths of electrical temporary wiring or long extension cords can cause ground fault leakage

current to flow by capacitive and inductive coupling. The combined leakage current can exceed 5 mA causing the GFCI

to trip—“ nuisance tripping.” GFCIs are now available that can be fastened to your belt. You can plug the extension cord

into the GFCI and use the protected duplex to power lighting and power tools. This is the ideal GFCI for construction and

maintenance workers. It also allows the GFCI to be near the user location, thereby reducing nuisance trips.

Other nuisance tripping may be caused by:

• Outdoor GFCIs not protected from rain or water

• Bad electrical equipment with case to hot conductor fault

• Too many power tools on one GFCI branch

• Resistive heaters

• Coiled extension cords ( long lengths)

• Poorly installed GFCI

27

Receptacle

Type

Circuit Breaker

Type

Portable Type

Figure 21

Typical Types of GFCIs

• Electromagnetic induced current near high voltage lines

• Portable GFCI plugged into a GFCI protected branch circuit

Remember that a GFCI does not prevent shock. It limits the duration of the shock so that the heart does not go

into ventricular fibrillation. The shock lasts about 1/ 40 of a second and can be intense enough to knock a person off a

ladder or otherwise cause an accidental injury. Also, remember that the GFCI does not protect against line- to- line

shock. Be sure to check insulation and connections on power tools each time before use.

Overview of the Safety Model

What Must Be Done to Be Safe?

Use the three- stage safety model: recognize, evaluate and control hazards. To be safe, you must think about your job

and plan for hazards. To avoid injury or death, you must understand and recognize hazards. You need to evaluate the situ-ation

you are in and assess your risks. You need to control hazards by creating a safe work environment, by using safe

work practices, and by reporting hazards to a supervisor, trainer or appropriate person( s).

• Use the safety model to recognize, evaluate and control hazards.

• Identify electrical hazards.

• Don’t listen to reckless, dangerous people.

If you do not recognize, evaluate and control hazards, you may be injured or killed by the

electricity itself, electrical fires or falls. If you use the safety model to recognize, evaluate, and

control hazards, you are much safer.

Stage 1: Recognize Hazards

The first part of the safety model is recognizing the hazards around you. Only then can you

avoid or control the hazards. It is best to discuss and plan hazard recognition tasks with your

co- workers. Sometimes we take risks ourselves, but when we are responsible for others, we are

more careful. Sometimes others see hazards that we overlook. Of course, it is possible to be

talked out of our concerns by someone who is reckless or dangerous. Don’t take a chance.

Careful planning of safety procedures reduces the risk of injury. Decisions to lock out and tag out circuits and equipment

need to be made during this part of the safety model. Plans for action must be made now.

Stage 2: Evaluate Hazards

When evaluating hazards, it is best to identify all possible hazards first, then evaluate the

risk of injury from each hazard. Do not assume the risk is low until you evaluate the hazard.

It is dangerous to overlook hazards. Jobsites are especially dangerous because they are

always changing. Many people are working at different tasks. Jobsites are frequently

exposed to bad weather. A reasonable place to work on a bright, sunny day might be very

hazardous in the rain. The risks in your work environment need to be evaluated all the time.

Then, whatever hazards are present need to be controlled.

• Evaluate your risk.

Stage 3: Control Hazards

Once electrical hazards have been recognized and evaluated, they must be controlled. You control electrical hazards in

two main ways: ( 1) create a safe work environment and ( 2) use safe work practices. Controlling electrical hazards ( as

well as other hazards) reduces the risk of injury or death.

28

Report hazards to your

supervisor, trainer or

other personnel as

appropriate.

OSHA regulations, the NEC and the National Electrical Safety Code ( NESC) provide a wide range of safety informa-tion.

Although these sources may be difficult to read and understand at first, with practice they can become very useful

tools to help you recognize unsafe conditions and practices. Knowledge of OSHA standards is an important part of

training for electrical apprentices. See the appendix for a list of relevant standards.

Always lock out and tag out

circuits.

• Take steps to control hazards:

• Create a safe workplace.

• Work safely.

Safety Model Stage 1— Recognizing

Hazards

How Do You Recognize Hazards?

The first step toward protecting yourself is

recognizing the many hazards you face on the

job. To do this, you must know which situa-tions

can place you in danger. Knowing where

to look helps you to recognize hazards.

Workers face many hazards on the job:

• Inadequate wiring is dangerous.

• Exposed electrical parts are dangerous.

• Overhead powerlines are dangerous.

• Wires with bad insulation can give you a

shock.

• Electrical systems and tools that are not grounded or double- insulated are dangerous.

• Overloaded circuits are dangerous.

• Damaged power tools and equipment are electrical hazards.

• Using the wrong PPE is dangerous.

• Using the wrong tool is dangerous.

• Some on- site chemicals are harmful.

• Defective ladders and scaffolding are dangerous.

• Ladders that conduct electricity are dangerous.

• Electrical hazards can be made worse if the worker, location or equipment is wet.

Inadequate Wiring Hazards

An electrical hazard exists when the wire is too small a gauge

for the current it will carry. Normally, the circuit breaker in a cir-cuit

is matched to the wire size. However, in older wiring, branch

lines to permanent ceiling light fixtures could be wired with a

smaller gauge than the supply cable. Let’s say a light fixture is

replaced with another device that uses more current. The current

capacity ( ampacity) of the branch wire could be exceeded. When

a wire is too small for the current it is supposed to carry, the wire

will heat up. The heated wire could cause a fire. Again, keep in

mind and consider the following wiring hazards to ensure proper

safety:

29

Use the safety model to recognize, evaluate, and control workplace hazards

like those in this picture.

An electrician was removing a metal fish tape from a hole at the base of a metal light pole. ( A fish tape is used to pull

wire through a conduit run.) The fish tape became energized, electrocuting him. As a result of its inspection, OSHA

issued a citation for three serious violations of the agency’s construction standards. If the following OSHA require-ments

had been followed, this death could have been prevented.

• De- energize all circuits before beginning work.

• Always lock out and tag out de- energized equipment.

• Companies must train workers to recognize and avoid unsafe conditions associated with their work.

Worker was electrocuted while

removing energized fish tape.

Fish tape.

• Wire gauge— wire size or diameter ( technically, the cross- sectional area).

• Ampacity— the maximum amount of current a wire can carry safely without overheating.

• Overloaded wires get hot.

When you use an extension cord, the size of the wire you are placing into the circuit may be too small for the equip-ment.

The circuit breaker could be the right size for the circuit but not right for the smaller- gauge extension cord. A tool

plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker. The

wire will overheat and could cause a fire. The kind of metal used as a conductor can cause an electrical hazard. Special

care needs to be taken with aluminum wire. Since it is more brittle than copper, aluminum wire can crack and break more

easily. Connections with aluminum wire can become loose and oxidize if not made properly, creating heat or arcing. You

need to recognize that inadequate wiring is a hazard. Incorrect wiring practices can cause fires.

Exposed electrical parts hazards

Electrical hazards exist when wires or other electrical parts are exposed. Wires and

parts can be exposed if a cover is removed from a wiring or breaker box. The overhead

wires coming into a home may be exposed. Electrical terminals in motors, appliances and

electronic equipment may be exposed. Older equipment may have exposed electrical

parts. If you contact exposed live electrical parts, you will be shocked. You need to recog-nize

that an exposed electrical component is a hazard.

• If you touch live electrical parts, you will be shocked.

Overhead Power Line Hazards

Most people do not realize that overhead power lines are usually not insulated. More

than half of all electrocutions are caused by direct worker contact with energized power

lines. Power line workers must be especially aware of the dangers of overhead lines. In

the past, 80 percent of all lineman deaths were caused by contacting a live wire with a

bare hand. Due to such incidents, all linemen now wear special rubber gloves that protect

them up to 34,500 volts. Today, most electrocutions involving overhead power lines are

caused by failure to maintain proper work distances.

• Overhead power lines kill many workers!

Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump

trucks, cranes, work platforms or other conductive materials ( such as pipes and ladders) contact overhead wires, the

equipment operator or other workers can be killed. If you do not maintain required clearance distances from power lines,

you can be shocked and killed. ( The minimum distance for voltages up to 50 kV is 10 feet. For voltages over 5 kV, the

minimum distance is 10 feet plus 4 inches for every 10 kV over 50 kV.) Never store materials and equipment under or

near overhead power lines. You need to recognize that overhead power lines are a hazard.

30

This hand- held sander has

exposed wires and should not

be used.

Watch out for exposed

electrical wires around

electronic equipment.

Electrical line workers

need special training and

equipment to work safely.

Operating a crane near overhead wires is

very hazardous.

Example of overhead power lines hazard

Defective Insulation Hazards

Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber cover-ing

insulates wires. Insulation prevents conductors from coming in contact with each other. Insulation

also prevents conductors from coming in contact with people.

• Insulation— material that does not conduct electricity easily.

Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or

appliance is damaged. When insulation is damaged, exposed metal parts may become energized if a

live wire inside touches them. Electric hand tools that are old, damaged or misused may have damaged

insulation inside. If you touch damaged power tools or other equipment, you will receive a shock. You

are more likely to receive a shock if the tool is not grounded or double- insulated. ( Double- insulated

tools have two insulation barriers and no exposed metal parts.) You need to recognize that defective

insulation is a hazard.

• If you touch a damaged live power tool, you will be shocked.

• A damaged live power tool that is not grounded or double insulated is very dangerous.

Improper Grounding Hazards

When an electrical system is not grounded properly, a hazard exists. The most common OSHA

electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical

wiring system that we touch ( switch plates, ceiling light fixtures, conduit, etc.) should be grounded

and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts

of motors, appliances or electronics that are plugged into improperly grounded circuits may be energized. When a circuit

is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. If there is no safe path to

ground for fault currents, exposed metal parts in damaged appliances can become energized. Extension cords may not

provide a continuous path to ground because of a broken ground wire or plug. If you contact a defective electrical device

that is not grounded ( or grounded improperly), you will be shocked. You need to recognize that an improperly grounded

electrical system is a hazard.

• Fault current— any current that is not in its intended path.

• Ground potential— the voltage a grounded part should have; 0 volts relative to ground.

• If you touch a defective live component that is not grounded, you will be shocked.

Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is

used as a path to ground for fault current, all pipes must be made of conductive material ( a type of metal). Many electro-cutions

and fires occur because ( during renovation or repair) parts of metal plumbing are replaced with plastic pipe,

which does not conduct electricity. In these cases, the path to ground is interrupted by nonconductive material. A ground

31

Five workers were constructing a chain- link fence in front of a house, directly below a 7,200- volt energized power line.

As they prepared to install 21- foot sections of metal top rail on the fence, one of the workers picked up a section of rail

and held it up vertically. The rail contacted the 7,200- volt line, and the worker was electrocuted. Following inspection,

OSHA determined that the employee who was killed had never received any safety

training from his employer and no specific instruction on how to avoid the hazards

associated with overhead power lines.

In this case, the company failed to obey these regulations:

• Employers must train their workers to recognize and avoid unsafe conditions on the

job.

• Employers must not allow their workers to work near any part of an electrical circuit

UNLESS the circuit is de- energized ( shut off) and grounded, or guarded in such a

way that it cannot be contacted.

• Ground- fault protection must be provided at construction sites to guard against elec-trical

shock.

This extension

cord is damaged

and should not

be used.

fault circuit interrupter, or GFCI, is an inexpensive life- saver. GFCI’s detect any difference in current between the two cir-cuit

wires ( the black wires and white wires). This difference in current could happen when electrical equipment is not

working correctly, causing leakage current. If leakage current ( a ground fault) is detected in a GFCI- protected circuit, the

GFCI switches off the current in the circuit, protecting you from a dangerous shock. GFCI’s are set at about 5 mA and are

designed to protect workers from electrocution. GFCI’s are able to detect the loss of current resulting from leakage

through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit.

GFCI’s are different from circuit breakers because they detect leakage currents rather than overloads. Circuits with miss-ing,

damaged, or improperly wired GFCI’s may allow you to be shocked. You need to recognize that a circuit improperly

protected by a GFCI is a hazard.

• GFCI— ground fault circuit interrupter- a device that detects current leakage from a cir-cuit

to ground and shuts the current off.

• Leakage current— current that does not return through the intended path but instead

“ leaks” to ground.

• Ground fault��� a loss of current from a circuit to a ground connection.

Overload Hazards

Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components

in an electrical system or circuit have a maximum amount of current they can carry safely. If too many devices are

plugged into a circuit, the electrical current will heat the wires to a very high temperature. If any one tool uses too much

current, the wires will heat up.

• Overload— too much current in a circuit.

• An overload can lead to a fire or electrical shock.

The temperature of the wires can be high enough to cause a fire. If their insulation melts,

arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a

wall. In order to prevent too much current in a circuit, a circuit breaker or fuse is placed in the

circuit. If there is too much current in the circuit, the breaker “ trips” and opens like a switch. If

an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the

circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical

current. If the breakers or fuses are too big for the wires they are supposed to protect, an over-load

in the circuit will not be detected and the current will not be shut off. Overloading leads to

overheating of circuit components ( including wires) and may cause a fire. You need to recognize that a circuit with

improper overcurrent protection devices— or one with no overcurrent protection devices at all— is a hazard.

• Circuit breaker— an overcurrent protection device that automatically shuts off the current in a circuit if an overload

occurs.

• Trip— the automatic opening ( turning off) of a circuit by a GFCI or circuit breaker.

• Fuse— an overcurrent protection device that has an internal part that melts and shuts off the current in a circuit if

there is an overload.

• Circuit breakers and fuses that are too big for the circuit are dangerous.

• Circuits without circuit breakers or fuses are dangerous.

Overcurrent protection devices are built into the wiring of some electric motors, tools and electronic devices. For

example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself.

Damaged tools can overheat and cause a fire. You need to recognize that a damaged tool is a hazard.

• Damaged power tools can cause overloads.

Wet Conditions Hazards

Working in wet conditions is hazardous because you may become an easy path for electrical current. If you touch a live

wire or other electrical component— and you are well- grounded because you are standing in even a small puddle of

water— you will receive a shock.

• Wet conditions are dangerous.

32

GFCI receptacle

Overloads are a major

cause of fires.

Damaged insulation, equipment or tools can expose you to live electrical parts. A damaged tool may not be grounded

properly, so the housing of the tool may be energized, causing you to receive a shock. Improperly grounded metal switch

plates and ceiling lights are especially hazardous in wet conditions. If you touch a live electrical component with an unin-sulated

hand tool, you are more likely to receive a shock when standing in water. But remember: you don’t have to be

standing in water to be electrocuted. Wet clothing, high humidity and perspiration also increase your chances of being

electrocuted. You need to recognize that all wet conditions are hazards.

• An electrical circuit in a damp place without a GFCI is dangerous. A GFCI reduces the danger.

Additional Hazards

In addition to electrical hazards, other types of hazards are present at job sites. Remember that

all of these hazards can be controlled.

• There may be chemical hazards. Solvents and

other substances may be poisonous or cause dis-ease.

• Frequent overhead work can cause tendinitis

( inflammation) in your shoulders.

• Intensive use of hand tools that involve force or

twisting can cause tendinitis of the hands, wrists

or elbows. Use of hand tools can also cause

carpal tunnel syndrome, which results when

nerves in the wrist are damaged by swelling ten-dons

or contracting muscles.

Examples of Additional Hazards ( Non- electrical)

• PPE— personal protective equipment ( eye protection, hard hat, special clothing, etc.)

• Low back pain can result from lifting objects the wrong way or carrying heavy loads of wire

or other material. Back pain can also occur as a result of injury from poor working surfaces

such as wet or slippery floors. Back pain is common, but it can be disabling and can affect

young individuals.

• Chips and particles flying from tools can injure your eyes. Wear eye protection.

• Falling objects can hit you. Wear a hard hat.

• Sharp tools and power equipment can cause cuts and other injuries. If you receive a shock,

you may react and be hurt by a tool.

33

Overhead work can

cause long- term

shoulder pain.

Frequent use of some hand tools can

cause wrist problems such as carpal

tunnel syndrome.

A 22- year- old carpenter’s apprentice was killed when he was struck in the head by a nail fired from a powder- actuated

nail gun ( a device that uses a gun powder cartridge to drive nails into concrete or steel). The nail gun operator fired

the gun while attempting to anchor a plywood concrete form, causing the nail to pass through the hollow form. The nail

traveled 27 feet before striking the victim. The nail gun operator had never received training on how to use the tool,

and none of the employees in the area was wearing PPE.

In another situation, two workers were building a wall while remodeling a house. One of the workers was killed when

he was struck by a nail fired from a powder- actuated nail gun. The tool operator who fired the nail was trying to attach

a piece of plywood to a wooden stud. But the nail shot though the plywood and stud, striking the victim. Below are

some OSHA regulations that should have been followed.

• Employees using powder- or pressure- actuated tools must be trained to use them safely.

• Employees who operate powder- or pressure- actuated tools must be trained to avoid firing into easily penetrated

materials ( like plywood).

• In areas where workers could be exposed to flying nails, appropriate PPE must be used.

Lift with your legs,

not your back!

• You can be injured or killed by falling from a ladder or scaffolding. If you receive a shock—

even a mild one— you may lose your balance and fall. Even without being shocked, you

could fall from a ladder or scaffolding.

• You expose yourself to hazards when you do not wear PPE.

All of these situations need to be recognized as hazards.

Summary

You need to be able to recognize that electrical shocks, fires, or falls result from these hazards:

• Inadequate wiring

• Exposed electrical parts

• Overhead powerlines

• Defective insulation

• Improper grounding

• Overloaded circuits

• Wet conditions

• Damaged tools and equipment

• Improper PPE

Safety Model Stage 2— Evaluating Hazards

How Do You Evaluate Your Risk?

After you recognize a hazard, your next step is to evaluate your risk from the hazard. Obviously, exposed wires should

be recognized as a hazard. If the exposed wires are 15 feet off the ground, your risk is low. However, if you are going to

be working on a roof near those same wires, your risk is high. The risk of shock is greater if you will be carrying metal

conduit that could touch the exposed wires. You must constantly evaluate your risk.

• Risk— the chance that injury or death will occur.

• Make the right decisions.

Combinations of hazards increase your risk. Improper grounding and a dam-aged

tool greatly increase your risk. Wet conditions combined with other hazards

also increase your risk. You will need to make decisions about the nature of haz-ards

in order to evaluate your risk and do the right thing to remain safe. There are

clues that electrical hazards exist. For example, if a GFCI keeps tripping while

you are using a power tool, there is a problem. Don’t keep resetting the GFCI and

continuing to work. You must evaluate the clue and decide what action should be

taken to control the hazard. There are a number of other conditions that indicate a

hazard.

• Short— a low- resistance path between a live wire and the ground, or

between wires at different voltages ( called a fault if the current is unintended).

• Tripped circuit breakers and blown fuses show that too much current is flowing in a circuit. This condition could be

due to several factors, such as malfunctioning equipment or a short between conductors. You need to determine the

cause in order to control the hazard.

• An electrical tool, appliance, wire or connection that feels warm may indicate too much current in the circuit or

equipment. You need to evaluate the situation and determine your risk.

• An extension cord that feels warm may indicate too much current for the wire size of the cord. You must decide

when action needs to be taken.

• A cable, fuse box or junction box that feels warm may indicate too much current in the circuits.

• A burning odor may indicate overheated insulation.

34

You need to be espe-cially

careful when

working on scaffold-ing

or ladders.

Combinations of hazards increase risk.

• Worn, frayed or damaged insulation around any wire or other conductor is an electrical hazard because the conduc-tors

could be exposed. Contact with an exposed wire could cause a shock. Damaged insulation could cause a short,

leading to arcing or a fire. Inspect all insulation for scrapes and breaks. You need to evaluate the seriousness of any

damage you find and decide how to deal with the hazard.

• A GFCI that trips indicates there is current leakage from the circuit. First you must decide the probable cause of the

leakage by recognizing any contributing hazards. Then you must decide what action needs to be taken.

Summary

• Look for “ clues” that hazards are present.

• Evaluate the seriousness of hazards.

• Decide if you need to take action.

• Don’t ignore signs of trouble.

Safety Model Stage 3— Controlling Hazards: Safe Work Environment

How Do You Control Hazards?

In order to control hazards, you must first create a safe work environment, then work in a safe manner. Generally, it is

best to remove the hazards altogether and create an environment that is truly safe. When OSHA regulations and the NEC

are followed, safe work environments are created. But you never know when materials or equipment might fail. Prepare

yourself for the unexpected by using safe work practices. Use as many safeguards as possible. If one fails, another may

protect you from injury or death.

How Do You Create a Safe Work Environment?

A safe work environment is created by controlling contact with electrical voltages and the currents they can cause.

Electrical currents need to be controlled so they do not pass through the body. In addition to preventing shocks, a safe

work environment reduces the chance of fires, burns and falls. You need to guard against contact with electrical voltages

and control electrical currents in order to create a safe work environment. Make your environment safer by doing the fol-lowing:

• Treat all conductors— even “ de- energized” ones— as if they are energized until they are locked out and tagged.

• Lock out and tag out circuits and machines.

• Prevent overloaded wiring by using the right size and type of wire.

• Prevent exposure to live electrical parts by isolating them.

• Prevent exposure to live wires and parts by using insulation.

• Prevent shocking currents from electrical systems and tools by grounding them.

• Prevent shocking currents by using GFCIs.

• Prevent too much current in circuits by using overcurrent protection devices.

Lock Out and Tag Out Circuits and Equipment

Create a safe work environment by locking out and tagging out circuits and machines. Before working on a circuit, you

must turn off the power supply. Once the circuit has been shut off and de- energized, lock out the switchgear to the circuit

so the power cannot be turned back on inadvertently. Then tag out the circuit with an easy- to- see sign or label that lets

everyone know that you are working on the circuit. If you are working on or near machinery, you must lock out and tag

out the machinery to prevent startup. Before you begin work, you must test the circuit to make sure it is de- energized.

35

Lockout/ Tagout Checklist

Lockout/ tagout is an essential safety procedure that protects work-ers

from injury while working on or near electrical circuits and equip-ment.

Lockout involves applying a physical lock to the power

source( s) of circuits and equipment after they have been shut off and

de- energized. The source is then tagged out with an easy- to- read tag

that alerts other workers in the area that a lock has been applied.

Disconnecting means required by Subjpart S must be capable of

accepting a lock ( consistent with 1910.147( c)( 2)( iii)).

In addition to protecting workers from electrical hazards, lockout/ tagout prevents contact with

operating equipment parts: blades, gears, shafts, presses, etc. When performing lockout/ tagout on

circuits and equipment, you can use the checklist items below as a guide.

• Identify all sources of electrical energy for the equipment or circuits in question.

• Disable backup energy sources such as generators and batteries.

• Identify all shutoffs for each energy source.

• Notify all personnel that equipment and circuitry must be shut off, locked out and tagged out. ( Simply turning a

switch off is NOT enough.)

• Shut off energy sources and lock switchgear in the OFF position. Each worker should apply his or her individual

lock. Do not give your key to anyone.

• Test equipment and circuitry to make sure they are de- energized. This must be done by an authorized person. ( An

“ authorized” person is defined as someone who has received required training on the hazards and on the construc-tion

and operation of equipment involved in a task.) ( See 1910.147( b) as applicable.)

• Deplete stored energy by bleeding, blocking, grounding, etc.

�� Apply a tag to alert other workers that an energy source or piece of equipment has been locked out.

• Make sure everyone is safe and accounted for before equipment and circuits are unlocked and turned back on. Note

that only an authorized person may determine when it is safe to re- energize circuits.

Control Inadequate Wiring Hazards

Electrical hazards result from using the wrong size or type of wire. You must control such hazards to create a safe work

environment. You must choose the right size wire for the amount of current expected in a circuit. The wire must be able to

handle the current safely. The wire’s insulation must be appropriate for the voltage and tough enough for the environment.

Connections need to be reliable and protected.

• Use the right size and type of wire.

• AWG— American Wire Gauge— a measure of wire size.

36

Always test a circuit to make sure it is

de- energized before working on it. Lockout/ tagout saves lives.

Control Hazards of Fixed Wiring

The wiring methods and size of conductors used in a system depend on several factors:

• Intended use of the circuit system

• Building materials

• Size and distribution of electrical load

• Location of equipment ( such as underground burial)

• Environmental conditions ( such as dampness)

• Presence of corrosives

• Temperature extreme

Fixed, permanent wiring is better than extension cords, which can be misused and

damaged more easily. NEC requirements for fixed wiring should always be followed. A

variety of materials can be used in wiring applications, including nonmetallic sheathed

cable ( Romex ® ), armored cable, and metal and plastic conduit. The choice of wiring

material depends on the wiring environment and the need to support and protect wires.

• Fixed wiring— the permanent wiring installed in homes and other buildings.

Aluminum wire and connections should be handled with special care. Connections

made with aluminum wire can loosen due to heat expansion and oxidize if they are not

made properly. Loose or oxidized connections can create heat or arcing. Special clamps

and terminals are necessary to make proper connections using aluminum wire.

Antioxidant paste can be applied to connections to prevent oxidation.

37

Wires come in different sizes. The maximum current each size can conduct safely is shown.

Nonmetallic sheathing helps

protect wires from damage.

Control Hazards of Flexible Wiring

Use Flexible Wiring Properly

Electrical cords supplement fixed wiring by providing the flexibility required for maintenance, portability, isolation

from vibration, and emergency and temporary power needs. Flexible wiring can be used for extension cords or power

supply cords. Power supply cords can be removable or permanently attached to the appliance.

• Flexible wiring— cables with insulated and stranded wire that bends easily.

DO NOT use flexible wiring in situations where frequent inspection would be difficult, where damage would be likely,

or where long- term electrical supply is needed. Flexible cords cannot be used as a substitute for the fixed wiring of a

structure. Flexible cords must not be:

• Run through holes in walls, ceilings or floors.

• Run through doorways, windows or similar openings ( unless physically protected).

• Attached to building surfaces ( except with a tension take- up device within 6 feet of the supply end).

• Hidden in walls, ceilings or floors.

• Hidden in conduit or other raceways.

Use the Right Extension Cord

The size of wire in an extension cord must be compatible with the amount of current the cord will be expected to carry.

The amount of current depends on the equipment plugged into the extension cord. Current ratings ( how much current a

device needs to operate) are often printed on the nameplate. If a power rating is given, it is necessary to divide the power

rating in watts by the voltage to find the current rating. For example, a 1,000- watt heater plugged into a 120- volt circuit

will need almost 10 amps of current. Let’s look at another example: A 1- horsepower electric motor uses electrical energy

at the rate of almost 750 watts, so it will need a minimum of about 7 amps of current on a 120- volt circuit. But electric

motors need additional current as they startup or if they stall, requiring up to 200 percent of the