4 main types of electrical injuries
electrocution (death due to electrical shock), electrical shock, burns, and falls
energized (live, "hot")
similar terms meaning that a voltage is present that can cause a current, so there is a possibility of getting shocked
When a circuit, electrical component, or equipment is energized
a potential shock hazard is present.
Slight shock felt. Disturbing, but not painful. Most people can "let go." However, strong involuntary movements can cause injuries.
(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."
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.
Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!
NEC—National Electrical Code
a comprehensive listing of practices to protect workers and equipment from electrical hazards such as fire and electrocution
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
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
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.
You control electrical hazards in two main ways:
(1) create a safe work environment and (2) use safe work practices.
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
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 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)
current that does not return through the intended path but instead "leaks" to ground
an overcurrent protection device that automatically shuts off the current in a circuit if an overload occurs
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.
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,
lock out and tag out the machinery to prevent startup.
The wire's insulation must be appropriate for the_____ and______ enough for the environment
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.
Connections made with aluminum wire can_____ due to heat expansion and _____ if they are not made properly
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
❑ 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 size of wire in an extension cord must be compatible with the
amount of current the cord will be expected to carry.
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
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.
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.
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.
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.
Bonding jumpers are necessary because
plastic does not conduct electricity and would interrupt the path to ground.
overcurrent protection device
(circuit breaker or fuse) designed to protect equipment and structures from fire
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.
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)
Power tools with metal housings or only one layer of effective insulation must have
a third ground wire and three-prong plug