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4 main types of electrical injuries

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


movement of electrical charge


Measure of electrical force


a complete path for the flow of current

You will receive a shock if

you touch two wires at different voltages at the same time.


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


material in which an electrical current moves easily


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

if you touch a live wire and are grounded at the same time.

You will receive a shock

When a circuit, electrical component, or equipment is energized

a potential shock hazard is present.

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.

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 9-30 milliamps (men) currents" start. It may not be possible to "let go."

50-150 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 (1-4.3 amps)

Ventricular fibrillation (heart pumping action not rhythmic) occurs. Muscles contract; nerve damage occurs. Death is likely.

10,000 milliamps
(10 amps)

Cardiac arrest and severe burns occur. Death is probable.

15,000 milliamps
(15 amps)

Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!

Severity of shock depends on

voltage, amperage, and resist- ance


a material's ability to decrease or stop electrical current


unit of measurement for electrical resistance

Lower resistance causes

greater currents.

NEC—National Electrical Code

a comprehensive listing of practices to protect workers and equipment from electrical hazards such as fire and electrocution


explosive release of molten material from equipment caused by high-amperage arcs


the luminous electrical dis- charge (bright, electrical sparking) through the air that occurs when high voltages 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. (2) A high-voltage arc can produce a considerable pressure wave blast. (3) A high-voltage arc can also cause many of the copper and alu-minum components in electrical equipment to melt

Class A fire extinguisher

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

Class B fire extinguisher

(think: Barrel) = flammable liquids

Class C fire extinguisher

(think: Circuits) = electrical fires

Burns are the most common injury caused by electricity. The three types of burns are

electrical burns, arc burns, and thermal contact burns.


Occupational Safety and Health Administration—the Federal agency in the U.S. Department of Labor that establishes and enforces workplace safety and health regulations

Electrical Fires

Electricity is one of the most common causes of fires and thermal burns in homes and workplaces

Thermal burns may result if

an explosion occurs when electricity ignites an explosive mixture of material in the air.

Electrical burns can result when

a person touches electrical wiring or equipment that is used or maintained improperly

If a Co-Worker Is Shocked or Burned by Electricity

(1) electricity shut-offs
("kill switches"), (2) first-aid sup- plies, and (3) a telephone so you can find them quickly in an emergency.

Three-stage safety model

recognize, evaluate, and control hazards.

You control electrical hazards in two main ways:

(1) create a safe work environment and (2) use safe work practices.

wire gauge

wire size or diameter (technically, the cross-sectional area)


the maximum amount of current a wire can carry safely without overheating

When the wire is too small a gauge for the current it is meant to carry

the wire will overload & heat up. The heated wire could cause a fire.

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 minimum distance for voltages up to 50kV is_____ . For voltages over 50kV, the minimum distance is ________________over 50kV.

10 feet, 10 feet plus 4 inches for every 10 kV


material that does not conduct electricity easily

Double-insulated tools have

two insulation barriers and no exposed metal parts

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

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 plumbing is used as a path to ground for fault current

all pipes must be made of conductive material (a type of metal).


ground fault circuit interrupter—a device that detects current leakage from a circuit to ground and shuts the current off. Detects any difference in current between the two circuit wires (the black wires and white wires)

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


too much current in a circut

circuit breaker

an overcurrent protection device that automatically shuts off the current in a circuit if an overload occurs


the automatic opening (turning off) of a circuit by a GFCI or circuit breaker


an overcurrent protection device that has an internal part that melts and shuts off the current in a circuit if there is an overload

If the breakers or fuses are too big for the wires they are supposed to protect

an overload in the circuit will not be detected and the cur- rent will not be shut off.

Damaged power tools

can cause overloads.


the chance that injury or death will occur

If exposed wires are 15 feet off the ground

your risk is low.


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)

to control hazards, you must first______, then _______

create a safe work environment, work in a safe manner

Guard against contact with _______ and ________control to create a safe work environment.

electrical voltages , electrical currents

Before working on a circuit, you

must turn off the power supply, then 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_____ the circuit to make sure it is ________.

test, de-energized.

You must choose the right size____ the amount of ______ expected in a circuit

wire for, current


American Wire Gauge— a measure of wire size.

The wire's insulation must be appropriate for the_____ and______ enough for the environment

voltage, tough

fixed wiring

the permanent wiring installed in homes and other buildings

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 extremes

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.

Special clamps and terminals are necessary to

make proper connections using aluminum wire

Connections made with aluminum wire can_____ due to heat expansion and _____ if they are not made properly

loosen, oxidize

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 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; or ❑ hidden in conduit or other raceways.


the amount of energy used in a second, measured in watts

1 horsepower =

746 watts

The size of wire in an extension cord must be compatible with the

amount of current the cord will be expected to carry.

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 cur- rent rating

AWG - The larger the gauge number

the smaller the wire!

Do not use extension cords that are

too long for the size of wire.

larger the size of the wire

the longer a cord can be without causing a voltage drop

A typical extension cord grounding system has four components:

❑ a third wire in the cord, called a ground wire; ❑ a three-prong plug with a grounding prong on one
end of the cord;
❑ a three-wire, grounding-type receptacle at the other end of the cord; and
❑ a properly grounded outlet.


a covering or barrier that separates you from live electrical parts

Isolation can be accomplished by

placing the energized parts at least 8 feet high and out of reach, or by guarding.

Take the following precautions to prevent injuries from contact with live parts:

❑ Immediately report exposed live parts to a supervisor or teacher.
❑ Provide guards or barriers if live parts cannot be enclosed completely.
❑ Use covers, screens, or partitions for guarding that require tools to remove them.
❑ Replace covers that have been removed from panels, motors, or fuse boxes.
❑ Even when live parts are elevated to the required height (8 feet), care should be taken when using objects (like metal rods or pipes) that can contact these parts.
❑ Close unused conduit openings in boxes so that foreign objects (pencils, metal chips, conductive debris, etc.) cannot get inside and damage the circuit.

Insulation is made of

material that does not conduct electricity (usually plastic, rubber, or fiber

short circuit

current passes through the shorting material without passing through a load in the circuit, and the wire becomes overheated

Bends in a cable must have an inside radius of at least

5 times the diameter of the cable so that insulation at a bend is not damaged.

The grounded conductors that complete a circuit are generally covered

with continuous white or gray insulation.

The ungrounded conductors, or "hot" wires, may be any color other than

green, white, or gray. They are usually black or red.

Conductors and cables must be marked by the manufacturer to show the following:

❑ maximum voltage capacity, ❑ AWG size, ❑ insulation-type letter, and ❑ the manufacturer's name or trademark.

Parts like switch plates, wiring boxes, conduit, cabinets, and lights need to be at_____ relative to ground.

0 volts


is connecting an electrical system to the earth with a wire.

A ground fault occurs when

current passes through the housing of an electrical device to ground

Equipment needs to be grounded under any of these circumstances:

❑ The equipment is within 8 feet vertically and 5 feet horizontally of the floor or walking surface.
❑ The equipment is within 8 feet vertically and 5 feet horizontally of grounded metal objects you could touch.
❑ The equipment is located in a wet or damp area and is not isolated. ❑ The equipment is connected to a power supply by cord and plug
and is not double-insulated.

For a GFCI to work properly, the neutral conductor (white wire) must

(1) be continuous, (2) have low resistance, and (3) have sufficient current-carrying capacity.

Test GFCI's regularly by pressing the____ button. If the circuit does not_____, the GFCI is faulty and must be replaced.

"test", turn off

The NEC requires that GFCI's be used in these high-risk situations:

❑ Electricity is used near water.
❑ The user of electrical equipment is grounded (by touching grounded material).
❑ Circuits are providing power to portable tools or outdoor receptacles.
❑ Temporary wiring or extension cords are used.

Specifically, GFCI's must be installed in

bathrooms, garages, out- door areas, crawl spaces, unfinished basements, kitchens, and near wet bars.


joining electrical parts to assure a conductive path

bonding jumper

the conductor used to connect parts to be bonded

Bonding jumpers are necessary because

plastic does not conduct electricity and would interrupt the path to ground.

Use overcurrent protection devices in____ to prevent_____

circuits, heating up or even melting

overcurrent protection device

(circuit breaker or fuse) designed to protect equipment and structures from fire

overcurrent protection device does not

protect you from electrical shock!

overcurrent protection devices are not allowed in areas where they could be exposed to______ because _______

physical damage or in hazardous environments, they can heat up and occasionally arc or spark, which could cause a fire or an explosion in certain areas.

A circuit breaker trips when

too much current passes through it

When too much current passes through the metal in the fuse, it

heats up within a fraction of a second and melts, opening the circuit

The NEC permits the use of portable tools only if they have been approved by

Underwriter's Laboratories (UL Listed)

Equipment that has two insulation barriers and no exposed metal parts is called

double- insulated.

double-insulated tools provide reliable shock protection without the need for

a third ground wire.

Power tools with metal housings or only one layer of effective insulation must have

a third ground wire and three-prong plug

OSHA defines PPE as

"equipment for the eyes, face, head, and extremities, protective clothing, respiratory devices, protective shields and barriers."

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