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NABCEP PV Installer Exam

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4 main types of electrical injuries
electrocution (death due to electrical shock), electrical shock, burns, and falls
current
movement of electrical charge
voltage
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 voltages at the same time.
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
conductor
material in which an electrical current moves easily
neutral
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
resistance
a material's ability to decrease or stop electrical current
ohm
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
arc-blast
explosive release of molten material from equipment caused by high-amperage arcs
arcing
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.
OSHA
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)
ampacity
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
insulation
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).
GFCI
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
overload
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
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
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.
risk
the chance that injury or death will occur
If exposed wires are 15 feet off the ground
your risk is low.
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)
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
AWG
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.
power
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.
guarding
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
Grounding
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.
bonding
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."