3 Electrical Safety

7/30/2019 3 Electrical Safety

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Occupational Safety and Health Administration

USA Department of Labor

OSHA OUTREACH SAFETY TRAINING

Mirdif Security & Safety Consultants

CONSTRUCTION INDUSTRY REGULATIONS

Subpart K Electrical Safety

29 CFR 1926.400 29 CFR 1926.408

Introduction:

Electricity is such an integral part of our lives at home and in workplace

that we can tend to take its power for granted. But heres a sobering fact.

The Bureau of Labor Statistics (BLS) in the United States of America

reported that during 1999, 278 (or about five percent) of work-related

deaths in the private sector in the United States resulted fromelectrocution. Dont become another tragic statistic.

Electrical accidents in the workplace can, for the most part, be avoided if

you use safe electrical equipment and work practices.

How Does Electricity Work:

To handle electricity safely, including working with equipment, you need to

understand how electricity acts, how it can be approached, the hazards it

presents, and how those hazards can be controlled.

Basically, there are two kinds of electricity: Static (stationary) Electricity

Dynamic (moving) Electricity

This guidance notes is about dynamic electricity because that is the kind

commonly put to use. Dynamic electricity is the flow of electrons through a

conductor. An electron is a tiny particle of matter that orbits around the

nucleus of an atom. Electrons of some atoms are easily moved out of their

orbits. This ability of electrons to move or flow is the basis of electrical

current.

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When you activate a switch to turn on an electric machine or tool, you allow

current to flow from the generating source through conductors (usually

wires) to the area of demand.

A complete circuit is necessary for the controlled flow of electrons along a

conductor. A complete circuit is made up of a source of electricity, a

conductor, and a consuming device (load).

VOLTS = CURRENT X RESISTANCE

Volts = Current x Resistance, is an equation known as Ohms Law. The

factors discussed below relate to one another as described by this equation.This relationship makes it possible to change the qualities of an electrical

current but keep an equivalent amount of power.

A force or pressure must be present before water will flow through a

pipeline. Similarly, electrons flow through a conductor because

electromotive force (EMF) is exerted. The unit of measure for EMF is volt.

For electrons to move in a particular direction, a potential difference must

exist between two points of the EMF source. For example a battery has

positive and negative poles.

The continuous movement of electrons past a given point is known asCurrent. It is measured in amperes. The movement of electrons along a

conductor meets with some opposition. This opposition is known as

Resistance. Resistance to the flow of electricity is measured in ohms. The

amount of resistance provided by different materials varies widely.

For example, most metals offer little resistance to the passage of electric

current. However, porcelain, wood, pottery, and some other substances have

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a very high resistance to the flow of electricity. In fact, these substances can

be used as insulators against the passage of electric current.

What are the Hazards of Electricity:

The primary hazards of electricity and its use are:

Shock

Burns

Arc-Blast

Fires and Explosions

Falls

Shock:

Electric currents travel in closed circuits through some kind of

conducting material. You get a shock when some part of your body

becomes part of an electric circuit. An electric current enter the body at

one point and exits the body at another location. High-voltage shocks can

cause serious injury (especially burns) or death.

You will get a shock if you touch:

1. Both wires of an electric circuit.

2. One wire of an energized circuit and ground.

3. Part of a machine, which is Hot because it is contacting an

energized wire and the ground.

Dont take any chances with electricity. One mistake can cost you your life.

The severity of the shock a person receives depends on several factors:

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How much electric current flows through the body.

What path the electric current takes through the body.

How much time elapses while the body is part of the electric

current.

The effect of an electric shock on a body can range from a tingle in the part

touching the circuit to immediate cardiac arrest. A severe shock can cause

more damage to the body than is readily visible.

Relatively small burn marks may be all that are visible on the outside.

However, a severely shocked person can suffer internal bleeding and severe

destruction of tissues, muscles, and nerves. Finally, a person receiving an

electric shock may suffer broken bones or other injuries that occur from

falling after receiving a shock.

Burns:

Burn can result when a person touches electrical wiring or equipment that is

improperly used or maintained. Typically, such burn injuries occur on thehands.

Arc-Blast:

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Arc-blasts occur when high-amperage currents jump from one conductor to

another through air, generally during opening or closing circuits, or when

static electricity is discharged. Fire may occur if the arcing takes place in an

atmosphere that contains an explosive mixture.

Explosions:

Explosions occur when electricity provides a source of ignition for an

explosive mixture in the atmosphere. Ignition can be due to overheated

conductors or equipment, or normal arcing (sparking) at switch contacts.

Fires:

Electricity is one of the most common causes of fire both in the home and

workplace. Defective or misused electrical equipment is a major cause, with

high resistance connections being one of the primary sources of ignition.

High resistance connections occur where wires are improperly spliced or

connected to other components such as receptacle outlets and switches.

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Heat develops in an electrical conductor from the flow of current. This heat

raises the temperature of the conductor. As a result, resistance in the

conductor increases, further raising the temperature. Thus, circuits

conducting a high rate of current and generating more resistance than it can

handle, may create enough heat to cause fire.

Causes of Electrical Accidents:

As a power source, electricity can create conditions resulting in bodily harm,

property damage, or both. It is important to you to understand how to avoid

electrical hazards when you work with electrical power tools, maintainelectrical equipment, or install equipment for electrical operation.

Accidents and injuries in working with electricity are caused by one or a

combination of the following factors:

Unsafe equipment and/or installation.

Unsafe workplaces caused by environmental factors.

Unsafe work practices.

Preventing Electrical Accidents:

Protection from electrical hazards is one way to prevent accidents caused byelectric current. Protective methods to control electrical hazards include:

Insulation.

Electrical protective devices.

Guarding.

Grounding.

PPE.

Good Work Practices

Insulation:Insulators of glass, mica, rubber, or plastic are put on electrical conductors to

protect you from electrical hazards. Before you begin to work on any piece

of electrical equipment, take a look at the insulation (on electrical cords, for

example) to be sure there are no exposed electrical wires. Also use insulated

tools.

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Electrical Protective Devices:

Electrical protective devices, including fuses, circuit breakers, and ground-

fault circuit-interrupters (GFCIs), are critically important to electrical safety.These devices interrupt current flow when it exceeds the capacity of the

conductor and should be installed where necessary.

Current can exceed the capacity of the conductor when a motor is

overloaded, for example, when you ask a 10 horsepower motor to do the

work of a 12 horsepower motor, or when a fault occurs, as when insulation

fails in a circuit.

When a circuit is overloaded, the insulation becomes brittle over time.

Eventually, it may crack and the circuit fails, or faults.

Fault occurs in two ways. Most of the time a fault will occur between a

conductor and an enclosure. This is called a ground fault. Infrequently, afault will occur between two conductors. This is called a short circuit.

A device which prevents current from exceeding the conductors capacity

creates a weak link in the circuit. In the case of a fuse, the fuse is destroyed

before another part of the system is destroyed. In the case of a circuit

breaker, a set of contacts opens the circuit. Unlike a fuse, a circuit breaker

can be reused by re-closing the contact. Fuses and circuit breakers are

designed to protect equipment and facilities, and in so doing, they also

provide considerable protection against shock.However the only electrical protective device whose sole purpose is to

protect people is the ground-fault circuit-interrupter. The GFCI is not an

over current device. It senses an imbalance in current flow over the normal

path and opens the circuit. GFCIs are usually installed on circuits that are

operated near water.

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Guarding:Any live parts of electrical equipment operating at 50 volts or more must

be guarded to avoid accidental contact. This protection can be accomplished

in several different ways. The machinery or equipment can be located:

In a room, enclosure, or vault accessible only to qualified personnel.

Behind substantial screens or partitions which prevent easy access.

On a balcony, platform, or gallery area which is elevated and not

accessible to unqualified/unauthorized persons.

At least eight feet above the floor of the work area.

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Any entrance to an area containing live parts of electrical equipment must

be marked with conspicuous warning signs. These signs should forbid

entrance except by qualified persons.

Grounding:

Grounding is necessary to protect you from electrical shock safeguard

against fire, and protect against damage to electrical equipment. There are

two kinds of grounding:

Electrical circuit or system grounding, accomplished when one

conductor of the circuit is intentionally connected to earth, protects

the circuit should lighting strike or other high voltage contact occur.

Grounding a system also stabilizes the voltage in the system so

expected voltage levels are not exceeded under normal conditions.

Electrical equipment grounding occurs when the equipment grounding

conductor provides a path of dangerous fault current to return to the

system ground at the supply source of the circuit should the insulation

fail.

When a tool or other piece of electrical equipment is grounded, a low-

resistance path is intentionally created to the earth. This path has enough

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current-carrying capacity to prevent any buildup of voltages in the

equipment which could pose a hazard to an employee using the equipment.

Therefore, never remove the ground prong from a plug because the

equipment no longer protects you from short circuits. If youre touching an

ungrounded tool, you will become the path of least resistance to the ground.

Grounding does not guarantee that an employee will never receive a shock,

or be injured or killed by electricity in the workplace. However, this simple

procedure will substantially reduce the likelihood of such accidents. Be sure

any equipment you work on is properly grounded.

Personal Protective Equipment:

If you work in an area where there are potential electrical hazards, your

employer must provide you with protective equipment. You must use

electrical protective equipment appropriate for the body parts that need

protection and for the work to be done. Electrical protective equipment

includes insulating blankets, matting, gloves, sleeves, overshoes, face

protection, and hard hats among other equipment specially made to protect

you from electricity.

Safe Work Practices for Handling Electricity:

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If your job requires you to work with electrical equipment, you need to have

a healthy respect for the power of electricity. In general, you should be sure

that any tools you use are in good repair, that you use good judgment when

working near electrical lines, and that you use appropriate protective

equipment. Remember if youre not sure, dont touch.

Lockout/Tag out:

A word to qualified employees about de-energizing electrical equipment

before you do any repairs on it or make an inspection. Common sense

dictates that electrical equipment be de-energized before working on it,when feasible. (Circumstances where it might be infeasible to de-energize

circuitry or equipment before working on it would include hazardous

location ventilation equipment or the testing of fire alarm systems, for

example, that can only be performed when the system is energized.

Qualified persons are only permitted to perform this kind of work.)

Having electrical current unexpectedly present when you are working on a

piece of equipment is no joke! Before any repair work or inspection of a

piece of electrical equipment is begun by an authorized person, the currentshould be turned off at the switch box, and the switch padlocked in the OFF

position.

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The other step in this procedure is the tagging of the switch or controls of

the machine or other equipment which is currently locked out of service. The

tag should indicate which circuits or pieces of equipment are out of service.

Work at Working Safely:Safety should be foremost in your mind when working with electrical

equipment. You face hazards from the tools themselves and the electricity

that powers them. Its up to you to wear protective equipment whenever its

specified, use all safety procedures, and work with tools correctly. Never let

over confidence or complacency lead to taking unnecessary risks. If yourenot sure dont touch. The following general rules apply to every piece of

electrical equipment you use:

Be sure your electrical equipment is maintained properly. Regularly

inspect tools, cords, grounds, and accessories. Make repairs only if

you are authorized to do so. Otherwise, arrange to have equipment

repaired or replaced immediately.

Be sure you use safely features like three-prong plugs, double-

insulated tools, and safety switches. Be sure machine guards are inplace and that you always follow proper procedures.

Install or repair equipment only if youre qualified and authorized to

do so. A faulty job may cause a fire or seriously injure you or other

workers.

Keep electric cables and cords clean and free from kinks. Never carry

equipment by its cords.

Use extension cords only when flexibility is necessary:

o Never use them as substitutes for fixed wiring.

o Never run them through holes in walls, ceilings, floors,doorways, or windows.

o Never use them where they are concealed behind walls,

ceilings, or floors.

Dont touch water, damp surfaces, ungrounded metal, or any bare

wires if you are not protected. Wear approved rubber gloves when

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working with live wires or ungrounded surfaces, and wear rubber-

soled shoes or boots when working on damp or wet surfaces.

Dont wear metal objects (rings, watches, etc.) when working with

electricity. They might cause arcing.

If you are working near overhead power lines of 50 kilo-Volts (kV) or

less, you or any equipment you are using must not come any closer

than 10 ft from the lines. Add 4 inches of distance for every 10 kV

over 50 kV.

Good work habits soon become second nature. Treat electricity with therespect it deserves and it will serve you efficiently and safely.

General Requirements: 29 CFR 1926.403 :

1- The conductors and equipment required or permitted by this

subpart shall be acceptable only if approved (U.L.).

2- Electrical equipment shall be free from recognized hazards that

are likely to cause death or serious harm to employees.

3- Listed or labeled equipment shall be used or installed in

accordance with any instructions included in the listing or labeling.4- Parts of electric equipment which in ordinary operation produce

arcs, sparks, flame, or molten metal shall be enclosed or separated and

isolated from all combustible material.

5- Marking of electrical equipment is very important. Marking

giving voltage, current, wattage, or other ratings shall be provided.

Marking plates shall be installed in such a manner so the marking can

be examined by the inspector without removing the installed

equipment from a hard wired position.

6- Each disconnect switch or over-current device required for a

service, feeder, or branch circuit must be clearly labeled to indicatethe circuit's function, and the label or marking should be located at the

point where the circuit originates.

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7- All labels and marking must be durable enough to withstand

weather, chemicals, heat, corrosion, or any other environment to

which they may be exposed.

600 Volts, Nominal, or Less:

Working Space About Electrical Equipment:

1- A minimum working space of 30 inch (76 cm) width is required

in front of electrical equipment operating at 600 volt or less. Distances

shall be measured from the live parts if they are exposed, or from the

enclosure front if the live parts are enclosed. This space permits

sufficient room to avoid body contact or elbows from contacting live

parts and metal parts at the same time while working on the

equipment. Equipment doors and hinged panels must have at least a

90 degree opening provided in the workplace.

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2- Working space is not required in back of electrical equipment

where there are not any removable or adjustable parts such as circuit

breakers, fuses, or switches mounted on the back of the equipment.

All connections and services areas for maintenance must be accessible

from other locations other than the back of the equipment.

3- Where the electrical equipment is installed in or on one wall

with the wall on the other side being an insulated wall (Constructed

from wood or metal studs with the wallboard consisting of sheetrock,

wood-panels, and etc.) the minimum workspace distance shall be 36inch (91 cm) between the equipment and the wall.

4- Where the electrical equipment is installed one wall with the

wall on the other side being a conductive wall, the distance shall be

minimum of 36 inch (91 cm) for voltage ranging from 0 to 150 V, andthe distance shall be 42 inch (106 cm) for voltage ranging from 151 to

600 V.

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5- Where the electrical equipment is installed in or on one wall

with the wall on the other side having electrical equipment mounted

or set on it. The distance shall be minimum 36 inch (91 cm) in case of

voltage ranging from 0 to 150 V. and shall be minimum 48 inch (122

cm) in case of voltage ranging from 151 to 600 V.

6- Working space in front of electrical equipment must be free

from storage of materials and etc. Mains and over-current protection

devices are required to be accessible to the users in case of

emergencies.

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7- Easy and fast access to electrical devices is essential. Special

consideration should be given to electrical equipment that is over 6 ft.

(2m) wide with 1200 Amps or more of bus containing over-current

devices, switching devices, or control devices. Such equipment must

have a clearance of 24 inches (61 cm) wide and 6.5 ft. (2 m) high at

each end for safe exit in case of a ground fault.

8- Service equipment, switchboards, panel-boards, and motor

control centers installed indoors must be provided with adequate

lighting for the safety of electrical workers servicing such equipmentfrom the front or rear when live parts are accessible. Lighting fixtures

can be incandescent or fluorescent as long as they provide the proper

lighting for parts to be serviced.

Lighting fixtures must have a head room clearance of at least 6.5 ft. (2

m) to give personnel sufficient room to stand in front of electrical

equipment without a treat of their head or head gear contacting metal

etc.

9- A minimum headroom clearance of 6.5 ft. (2 m) must be

maintained from the floor or platform up to the lighting fixture or any

overhead obstruction.

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29 CFR 1926.404 Wiring Design and Protection:

Conductors used in electrical wiring systems must be identified properly to

protect personnel working on such systems. It is essential to know which

conductor by color represent the ungrounded hot phase conductor (live), the

grounded neutral conductor (neutral), and equipment grounded conductor

(earth) in electrical circuit. Because it is by color coding that conductors are

connected to color coded terminals of equipment.

The grounded neutral conductor of a branch circuit shall be identified by a

continuous white or natural gray color. It is an energized circuit conductor

that is connected to the earth through the system ground.

The equipment grounding conductor of a branch circuit shall be identified

by continuous green color or a continuous green color with one or more

yellow stripes unless it is bare. It is not an energized conductor under normal

conditions.

The ungrounded phase conductors can be identified with any color other

than those used for the grounded neutral conductors or equipment

conductors ( it could be Black, Blue, or Red)

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Reversed Polarity:

Many pieces of equipment will operate properly even though the supply

wires are not connected in the order designated by design or the

manufacturer. Improper connection of these conductors is most prevalent on

the smaller branch circuit typically associated with standard 120 volt

receptacle outlets, lighting fixtures and cord - and plug - connected

equipment.

When plugs, receptacles, and connectors are used in an electrical branch

circuit, correct polarity between the ungrounded (hot) conductor, the

grounded (neutral) conductor, and the grounding conductor must bemaintained.

Reversed polarity is a condition when the identified circuit conductor (the

grounded conductor or neutral) is incorrectly connected to the ungrounded

or (hot) terminal of a plug, receptacle, or other type of connector.

The figure above shows an extremely dangerous situation. In this example,

the black (ungrounded) and green (grounding) conductors have been

reversed. The metal case of the equipment is at 120 volts with reference to

the surroundings. As soon as a person picks up the equipment and touches a

conductive surface in their surrounding, he will receive a serious, or even

deadly, shock.

Although the equipment will not work with this wiring error, it would not be

unusual for a person to pick up the equipment before realizing this. The

person may even attempt to troubleshoot the problem before unplugging the

power cord.

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