3 electrical safety
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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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