Vol 4: Transformers and Distribution Systems Flashcards
Has removable soft-jaw inserts and pipe jaws.
Utility vise.
Used for forming wire loops.
Longnose pliers
Used for driving and removing screws.
Screwdrivers.
Uses a chain to grip its work.
Chain vise.
When turned backwards, releases its grip.
Pipe wrench.
Used for driving or pulling nails
Claw hammer
Used for turning nuts and bolts if the right size
box or open end wench is not available.
Adjustable jaw wrench.
Comes in standard sizes to fit nuts and bolts.
Box or open end wrench.
Used to assemble conduit and couplings.
Pipe wrench
Used to cut large wire and small cables.
Sidecutting plier
Can be mounted on legs and carried to the job sites.
Conventional pipe vise.
Equipped with adjustable jaws and extra-long
handles for gripping round stock.
Water pump pliers.
Used for driving stakes and ground rods.
Sledge hammer
Should not be used for a chisel or punch.
Screwdrivers.
Used to cut conduit, tubing, or flat metal.
Hacksaw
Used to cut rigid conduit only.
Rigid conduit cutter
Used to cut wood across the grain.
Carpenter’s saw.
Used to cut grooves in wood.
Wood chisel
Used to enlarge holes in metal.
Knockout punch
Used to cut and chip metal.
Cold chisel
May be used to strip insulation from wires.
Pocketknife.
Driven by hand pressure or with a mallet.
Wood chisel
Does not break out strip by twisting the tool.
Carpenter’s saw.
Using this tool on thin-wall conduit flattens the end.
Rigid conduit cutter
With this tool, a wrench is used to turn the bolt until a hole is made.
Knockout punch
A dull blade for this tool cannot be sharpened
Hacksaw
Requires a hole be drilled or punched before it can be used.
Knockout punch
On this tool, a cutting blade angle of 60 to 70° is fine for most
light metals.
Cold chisel
These tools range in size from 8 to 16 inches.
Hacksaw
When using this tool, two or more teeth should always be in
contact with the work.
Hacksaw
The cutting wheels must be replaced when dull.
Rigid conduit cutter.
A hammer and punch may be used to remove the slug from the die
of this tool.
Knockout punch
A cutting blade angle of 90° is recommended for cutting hard and
tough metal.
Cold chisel
Never use a metal hammer to drive this tool.
Wood chisel
Should be sharpened on an emery wheel and then honed on an oil
stone.
Wood chisel
Has a blade that can be used as a screwdriver.
Pocketknife
Cuts a 1-inch hole for 1-inch conduit.
Knockout punch
A coarse-toothed blade is used to cut soft metal.
Hacksaw
Used to drill holes in concrete or brick walls.
Star bit
Used for drilling holes in wood only.
Auger bit
Usually has a round shank.
Twist bit
Uses bits with a square tang.
Ratchet brace
Uses a twist bit and requires only hand pressure.
Hand drill
Uses a twist bit and allows pressure to be applied with the body.
Breast drill
What special tool do you use for pulling conductors (wires) through conduit, and how do you use it if
the conductors are very large?
Fish tape; to pull winch line or rope through first, then pull the winch line or rope to pull the conductors.
Which measurement tool does the electrician use for layout or roughing in boxes?
Folding rule.
How can you use the folding rule for taking inside measurements?
By extending the metal slide at one end.
What is the purpose of the wire gauge?
To measure the diameter of a wire or to check the size.
Why do you use a fuse puller when replacing fuses?
To eliminate the danger of electric shock.
When using the wire stripper, what precaution must you observe and why?
Make sure the size of wire being stripped is not larger than the slot. If you don’t, the wire may be nicked or cut
What tool removes the sharp edges from the inside of conduit after you cut it to length?
Reamer.
How do you determine the size of a drill?
By the size of the drill shank that will fit in the chuck
How are bits secured in an electric drill?
By a key-type gear chuck.
What types of bits do you ordinarily use with the electric drill?
Twist, spade, and masonry bits
Why do you need to apply pressure when using a spade bit?
The spade bit does not have a screw tip; therefore, pressure must be applied.
How would you avoid splintering the hole when using the spade bit?
By reducing the pressure before the drill goes through the wood.
What type of bit would you use to drill into concrete, cinder block, or brick?
Masonry bits.
How can you overload the electric hand drill?
By using oversized drill bits
When drilling metal with a twist bit and electric drill, what do you do just before breaking through to
avoid wedging the bit?
Reduce the pressure on the bit.
When cutting an opening in a finished wall with a saber saw, what must you do to make a starting
point for the blade?
Drill a pilot hole first.
How do you place the base plate of a saber saw on the material you are cutting?
Always apply steady, even pressure and hold the base plate firmly against the work.
Why is it important to replace the hydraulic fluid with what the manufacturer requires?
Using the wrong or mixing types of hydraulic fluid can damage the seals on the equipment
What are the major parts of the ram?
The piston, a cylinder, a compression spring, a hydraulic connector and some seals.
What size hole does a 1/2” conduit knockout make?
A ½” knockout makes a 7/8” hole that is required for ½” conduit fittings.
TW – Moisture-resistant thermoplastic.
Used in dry or wet locations
THW – Heat and moisture-resistant thermoplastic.
Used in dry or wet locations
RHW – Heat- and moisture-resistant rubber
Used in dry or wet locations.
Define wire.
A thin rod of hard or soft drawn metal that conducts easily, such as copper or aluminum.
Define conductor.
A bare or insulated wire or group of wires not insulated from each other, which is suitable for carrying current.
What is the difference between a solid and a stranded conductor?
A solid conductor is a single wire; a stranded conductor is a group of single wires twisted together.
Of the materials used for conductors today, which is the best?
Copper.
What is the size range of the American wire gauge (AWG)?
No. 40, the smallest, to No. 4/0, the largest.
Which is the larger conductor, a No. 2 AWG or a No. 20 AWG?
No. 2 AWG
How are conductors larger than No. 4/0 AWG sized and numbered?
Sized according to cross-sectional area and numbered according to thousand circular mils.
Why are larger conductors stranded?
For flexibility.
Why do conductors in conduit or cable have smaller amperage ratings than the same conductors run
in free air?
Conductors in conduit can not get rid of heat as fast as those in free air.
What are three reasons for electrical connections to be enclosed?
To reduce the chance of fire; to provide physical protection for wire terminals, splices, and electrical devices;
and to protect people from accident shock, burns, or possible electrocution.
What is the required enclosure for electrical connections?
Outlet and junction boxes.
What is the difference between an outlet box and a junction box?
An outlet box is for mounting a switch, outlet receptacle, or a lighting fixture, while a junction box encloses
connections or splices between conductors
Where do you locate splices in interior electrical systems?
Located in boxes.
What is another name for utility boxes?
Handy boxes.
Name two types of materials used to make boxes.
Metal and nonmetallic insulating material.
How do we prevent corrosion on boxes that are not made of corrosion-resistant material?
Boxes are galvanized, enameled, or coated with other corrosion-resistant material.
Where may we use nonmetallic boxes?
With nonmetallic wiring methods, such as nonmetallic sheathed cable or rigid nonmetallic conduit.
Describe a box knockout and state its purpose.
A prepunched disk that can be knocked out easily so that conduit or cable connectors can be installed
Describe a pry-out and explain when pry-outs are put in boxes.
A prepunched slotted piece that can be twisted out with a screwdriver. They are punched in boxes with built-in
cable clamps.
How are heavy light fixtures supported?
By use of a fixture stud.
When installing ceiling lights with conduit, what is the advantage of using octagonal boxes instead of
round boxes?
Conduit can be connected to the sides of the boxes as well as to the back.
What is a pull box?
A box that allows conductors to be pulled through conduit to an intermediate point in the circuit and then to the
end point without having to be cut and spliced
When wiring with conduit, what type of box do you use when conduit is to enter and leave the box on
the same side?
A square box
What is meant by ganging boxes together and when do we do it?
Ganging means to remove one side from two device boxes and then fasten them together by means of the side
retaining screws to form a large box that we use to mount two devices side by side.
What two uses can be made of utility boxes other than for surface-mounted switches or receptacles?
They may be used as junction boxes or for switches or receptacles in concealed wiring.
When considering the installation of a box for other than its primary purpose, which one should you
probably not consider?
A round box or ceiling pan
Describe an extension ring.
An extension ring looks similar to a box without a closed back. It has a narrow flange that provides a seat for
mounting the extension to a box.
What are three uses for extension rings?
To increase box capacity, to bring the edge of a box out flush with the wall surface when a box is mounted too
deep, and to extend the edge of an old box beyond the surface of a wall to permit the addition of surface wiring
How may installed switch boxes be used when a room is repaneled using ¾-inch furring strips and ¼-
inch plywood?
By using rings designed to extend existing boxes flush to the new wall. They are held in place by long screws
run through the devices and rings, and screwed into the original box mounting holes.
Why are box covers used on electrical systems?
To provide protection and a neat appearance.
What type of covers do round and square boxes require?
Round and square covers.
What do you use to increase box space?
A raised cover.
What determines the depth of a raised device cover?
The thickness of the wall surfacing materials.
A metal conduit made in sizes of 1/2 inch through 6 inches
that may be used in any location.
Galvanized rigid metal
conduit.
Used for connecting metal conduit to a box.
Locknuts and bushings
Uses threadless couplings that must be glued.
Rigid nonmetallic conduit
Also called thin-wall, conduit uses compression fittings
for coupling and connecting.
EMT.
Used as an alternate in place of rigid because of its light
weight.
Intermediate metal conduit
Cannot be used in lengths over 6 feet.
Flexible metal tubing
Used to fasten EMT to a box.
Compression connector
Used to fasten the ends of EMT together.
Compression couplings
Used for connecting vibrating equipment that requires
6-inch electrical trade size.
Flexible metal conduit
Flexible conduit with an outer jacket.
Liquid-tight flexible metal
conduit
What is the purpose of a switch?
To connect and disconnect electrical circuits or components to and from the power source.
How are switches rated?
Switches are rated according to voltage and amperage capacities
How do you mount single-pole toggle switches?
In a switch-box with the toggle pointed up when the switch is on and covered with a switch-plate.
How many terminals does a double-pole switch have?
Four.
What switches may control a light or lights from two locations?
Three-way switches.
How many terminals does a three-way switch have?
Three.
What switches control a light or lights from more than two locations?
Two three-way switches and one or more four-way switches, depending on the number of switching locations
required
How many conductor(s) and in what order must knife-blade switches equipped with three blades
open?
All conductors at the same time
How must a circuit breaker used as a switch for a 120-volt, fluorescent light circuit be marked?
SWD.
How many feet above the floor can you mount the handle of a circuit breaker that is to be used as a
switch for a 120-volt, fluorescent light circuit?
6 feet, 7 inches (79 inches).
What is the device called that completes the connection between the receptacle and the equipment
being served with power?
Attachment plug.
What is the function of a receptacle outlet?
To make it easy to connect and disconnect portable appliances, tools, and other electrical devices.
What precautions must you take when ordering a heavy-duty receptacle?
A heavy-duty receptacle is ordered for a specific voltage, amperage, and number of contact pins required.
Used frequently for window air-conditioners.
125/250 volt, 50-ampere receptacle.
Straight slot, used for ranges.
125/250 volt, 30-ampere receptacle
L-slot, used for dryers.
120 volt, three-wire duplex
Parallel slot, wired with an equipment ground.
220/440 volt, three-phase
receptacle.
Grooved case for alignment.
220/440 volt, three-phase
receptacle.
How are light fixtures classified?
According to the way they distribute light
What are the light fixture classifications?
Direct, semi-direct, general diffusing, semi-indirect, and indirect.
What percent of light is directed below the horizontal in the semi-direct classification?
60 to 90 percent.
What percent of light is directed below the horizontal in the semi-indirect classification?
10–40 percent.
In which light fixture classification is the light source concealed from view below the horizontal?
Indirect.
Which light fixture uses the entire ceiling as a light source?
Indirect.
Which is the most common measure of light output?
The lumen.
How do we measure illuminance?
In foot-candles
Which does the human eye see, illuminance or luminance?
Luminance.
Within a listed range of illuminance, what three factors dictate the proper level?
The task(s) being done (contrast, size, etc.), the ages of the occupants, the importance of speed and accuracy
What are the three quality issues of light?
Glare, uniformity of illuminance, and color rendition
How can we reduce glare?
By not exceeding suggested light levels and using lighting equipment that is designed to reduce glare.
What are some of the problems caused by non-uniform illuminance?
Inadequate light levels, Visual discomfort, Bright spots and patches of light on floors and walls that cause
distraction and generate a low quality appearance
Which is better, a color-rendering index a (CRI) of 50 or a CRI of 76?
76.
Why are lamps often coated either on the inside and/or on the outside?
These coatings allow for color and durability.
What is the source of light and heat given off by incandescent lamps?
The filament.
What type of gas is most commonly used in incandescent lamps?
Argon gas
What is the gas used in a halogen lamp?
Halogen gas.
How do we figure a bulb’s diameter?
Bulbs are measured through their greatest diameter in eighths of an inch.
Why are there so many designs of filaments?
These designs are selected for either the way they dissipate heat or disseminate the light.
What are the most commonly used incandescent bases?
Candelabra, intermediate, medium (also called an “Edison” base), and mogul bases.
What happens to the ultra violet energy produced by fluorescent lamps?
The ultra violet energy is absorbed by a phosphor coat on the inside of the glass tube and converted by the
phosphor to visible wavelengths; the wavelengths of the light are determined by the composition of the
phosphor.
What three inert gasses do fluorescent lamps usually contain?
Argon, Krypton, and neon
How do we express the color temperature of a light source?
Kelvins (K), a means of describing the apparent whiteness of the lamp.
How do we measure the nominal length of fluorescent lamps?
From the back of the lampholder to the back of the other lampholder
How many contacts are required for instant start fluorescent lamps?
Only two electrical contacts one at each lamp end.
When not specified, in what position is a HID lamp suitable for operation?
Any position.
What hazards are present when the outer envelope (glass bulb) of a HID lamp is broken or punctured?
Serious skin burn and eye inflammation from short-wave ultra-violet radiation.
Of what two main components do mercury vapor lamps consist?
An outer glass envelope and a quartz arc tube
How many electrodes are on the inner tube of a mercury vapor lamp?
Two main electrodes and a third starting electrode
List the general categories of electrical loads found in buildings.
Mainly, lighting with some motor operation, fairly heavy lighting with moderate requirement for power
equipment, and mostly power equipment with a small lighting load.
What type of electrical system would be needed to service a small building with lights only?
Two-wire, single-phase system.
What type of wiring system is needed in a residence where an electric range and dryer are installed?
Three-wire, single-phase system.
A pumphouse is being wired to provide power for three heavy-duty pumps. The pumps operate
unattended, starting and stopping automatically. What type of electrical system would this
pumphouse most likely have?
Three-phase, three-wire.
A building is provided with electrical power to operate several pieces of equipment that are using
208-volt motors ranging in size from 3 to 10 horsepower. Lighting is also a large requirement. What
type of electrical system is needed in this building?
Three-phase, four-wire system.
A building is provided power with a three-phase, four-wire system with a delta transformer hookup.
Why can only two-phase conductors be used to provide power for the lighting system?
Because the voltage from the third-phase conductor to the neutral is much higher than 120 volts and would burn
out any lights attached to it.
Explain the delta wild leg requirements in regard to color coding and phase relationship on
panelboards.
The wild leg is color-coded orange whenever it is in the same enclosure as the neutral. The phase relationship
on panelboards always has the wild leg in the center, or “B” position.
Core
Provides a magnetic path (circuit of low reluctance for the magnetic flux)
Primary winding
Receives energy from the AC source.
Secondary winding
Receives energy by mutual induction from the primary and delivers it to
the load.
Case
Protects the transformer from moisture and physical damage and also
helps to cool the transformer unit.
Power factor =
kW (true power) divided by
kVA (apparent power
pf =kW/kVA
Constant-potential transformers
A constant-potential transformer changes the voltage level of a system. Its primary is connected across a
steady voltage supply and provides a steady secondary voltage that is the same from no load to full load.
Power and distribution transformers are this type. The current in both the primary and secondary changes
when the load is changed.
Varying potential transformers
A varying-potential transformer varies the secondary voltage when connected to a constant primary
voltage. This type of transformer is found in a voltage regulator or a ballast for mercury-vapor lamps.
Current transformers
A current transformer changes the current of a system. Its primary winding is connected in series with the
desired circuit to change the current. The voltage on both the primary and secondary change with the
change in current in the system. This transformer is used in instrument transformers.
Constant-current transformers
A constant-current transformer supplies a constant secondary current to a system regardless of the load.
The primary is connected to a constant voltage, but the secondary voltage varies according to the load.
You use this transformer a lot in series street lighting and airfield lighting systems. It’s more commonly
called a constant-current regulator.
To find the kilovolt-ampere rating for a three-phase bank of transformers, use the following formula:
kVA=(E)(I)(1.723) DIVIDED BY 1000
Single-phase connections kVA=L=
(I)(V) / 1000
There are three basic types of distribution systems that the Air Force uses:
- Delta.
- Grounded wye.
- Ungrounded wye.
What are the principal parts of a transformer?
Core, primary winding, secondary winding, and the case.
What is the process by which a current is induced from one coil to another by use of an expanding
and contracting magnetic field?
Mutual induction.
What type of transformer loss is due to the reversing of the magnetic field in the core when AC
reverses direction in the windings?
Hysteresis loss.
What do we call the ratio of the true power to the apparent power?
Power factor.
What is the purpose of transformer oil?
To cool the coils and core, and also act as an insulating material.
What type of transformer oil has the highest dielectric strength?
Synthetic oil.
Why do you use a constant-potential transformer?
To change the voltage level of a system.
In what type of transformer does the current and voltage change when the load changes?
Constant-potential transformer.
What type of transformer has a secondary voltage that varies, but a current that remains the same?
Constant-current transformer.
How are the leads marked on a transformer?
High-voltage leads are marked “H” while the low-voltage leads are marked “X.”
How would you connect the secondary of a transformer if you want to increase the current-carrying
capacity?
In parallel.
Why are fuses enclosed?
To keep the melted metal from flying or dropping into nearby equipment and doing damage or causing a fire.
Enclosed:
The fiber tube drops down and is exposed from the bottom.
Open:
The fuse holder tube drops out and hangs down.
Open link:
The lower spring contact pulls the fuse link apart, leaving the pigtail hanging free.
List the main parts of the service drop and describe their functions.
The service drop has two, three, or four conductors, and fittings or insulators for attaching the conductors to the
building. The conductors serve to bring the power to the building from the distribution system. The fittings
provide insulated anchorage for the conductors.
What is the minimum clearance above the ground that the service drop may be attached to a building?
10 ft
How far must a service drop clear an alley?
18 ft
When a service drop is attached to the side of a building, how far must it be away from the side of a
window?
at least 3 ft
What components make up the service entrance system?
Conductors, service head, raceway, meter socket, service disconnect, overcurrent protector, panelboard, and
grounding electrode conductor.
What is the purpose of the service entrance system?
To bring power from the service drop into the building to a panel board
What is the purpose of the raceway on the service entrance system?
To protect the conductors from physical and weather damage.
What function does a service head perform in the service-entrance system?
The service head provides an entrance for conductors into a raceway and prevents rain from entering the
raceway. Bushings in the conductor-entry holes reduce insulation abrasion.
How can you keep water from entering a SE cable when a service head is not used?
The end of the SE cable is bent to form a gooseneck to keep rain out and the gooseneck is taped and painted or
taped with self-sealing, weather-resistant thermoplastic.
How can you determine the amount of power used in a building?
A meter socket is put in the service entrance in which a wattmeter is installed to record the power used.
Describe the arrangement and purpose of the service-entrance disconnects.
The disconnects consist of a combination of switches and overcurrent protective devices. The switches are
connected so that the entire interior wiring can be disconnected from the exterior power supply, and the
overcurrent devices protect the service conductors.
List three types of service-entrance disconnects.
Knife-blade switch, fuse block, disconnect, multi-pole-breaker assembly and single-pole switches or circuit
breakers (not to exceed six).
For what must power-operated service disconnects have a provision?
Manual opening.
Where does the service entrance end?
At a panelboard.
How must you fasten the grounded conductor to the bus bar?
It must be attached so it can be disconnected, such as with pressure connectors.
Name three types of grounding electrodes used in grounding our service entrance.
A metal pipe in the water system., metal structure of a building, and metal rods
Where do you install small grounding electrode conductors?
In a protective metal covering that should be electrically continuous from the panelboard cabinet to the
grounding electrode.
What means ensure all parts of the service entrance, the grounded conductor, and the grounding
electrode conductor are at the same potential electrically?
They are bonded together electrically.
What must you determine before installing a service entrance?
Size of the service-entrance conductors.
What is the power base needed for a building?
Lighting and small appliances, plus the power to operate heavier equipment, such as dryers, furnaces, and
motor-driven equipment.
What is the minimum amperage requirement for the service entrance of a single-family dwelling?
100 amperes.
Where can you find information on permissible methods of protecting SE conductors?
The National Electrical Code®.
What are the basic requirements for installing a service mast?
It is installed though the roof and may go down inside the wall between the studs. If used as support, the mast
must be strong enough to provide an anchor for the service drop.
What is the procedure for installing the service disconnect when it is a separate switch?
In surface-mounted boxes, installed on the inside wall directly behind the service-entrance conduit. The conduit
may enter the box from the back or top.
Where is a break in the SE conductors permitted?
Where a meter is included.
What is the maximum distance the weatherhead can be located from the service drop?
24 inches.
Why are drip loops provided in the service-drop conductors?
To prevent water from running down the service conductors into the weatherhead when it rains.
What precaution must you take when splicing copper-service conductors to aluminum service-drop
conductors?
Special connectors must be used to splice aluminum and copper conductors. These connectors prevent
electrolytic corrosion from occurring between the copper and aluminum.
How are service conductors connected to the switch terminals?
By pressure-type terminals.
Briefly describe the construction of a service-entrance cable.
A service-entrance cable has the insulated conductors wrapped with the stranded neutral conductor, which
provides some protection against physical damage and adds some stiffness.
How do you keep moisture out of the service drop end of a SE cable when a weatherhead is not used?
The end of the service entrance cable is formed into a gooseneck, which is then taped and painted or topped
with a self-sealing, weather-resistant thermoplastic.
What are the minimum support requirements for SE cable?
A cable clamp must be applied within 12 inches of the weatherhead, gooseneck, or connection to a raceway and
added clamps are required at points not more than 30 inches apart
What do we call the conductors of an underground system that bring power to a building?
Service laterals.
What are three ways we can connect the underground conductors for a building to the power source?
Overhead distribution system, underground secondary main, or to a transformer.
What are two ways you can install a service lateral?
It may be installed in rigid conduit, either metal or nonmetallic, or with underground SE cable
When do we use a terminal box with a service lateral?
When the meter is to be part of the system, the wiring method is changed, or multiple disconnects are used.
Where does the service entrance start when the service lateral connects directly to the service
equipment inside a building?
At the point of entry to the building.
By how many inches of dirt must a service lateral installed in rigid, nonmetallic conduit be protected?
At least 18 inches.
What protection is required for USE cable entering a building from underground?
The cable must be protected by an approved entrance or raceway from the point of entrance to below the ground
line and beyond the walls of the building.
Name three types of distribution panels.
Lighting and appliance panels, power panels, and feeder panels.
What is a lighting and appliance panelboard?
A panelboard that has more than 10 percent of its overcurrent devices protecting lighting and appliance branch
circuits.
What is the purpose of a power panelboard?
To provide power to electrical equipment, normally at 240/480 volts.
What type of panelboard is set up to furnish power to other panelboards?
Feeder panelboard.
Why would a panelboard furnish power to other panelboards?
This allows branch circuits where they are most useful, with an overall savings in material.
What information must appear on a panelboard?
The voltage, current rating, number of phases, and the manufacturer’s name or trademark.
What protection from current flow must be provided a panelboard?
It must be protected on the supply side by not more than two main circuit breakers on two sets of main fuses
having a combined rating no greater than that of the panelboard.
What are the grounding requirements for panelboards where wiring is done with nonmetallic cable?
A terminal bar must be provided for attachment of feeder and branch circuit equipment-grounding conductors.
This terminal bar must also be bonded to the cabinet.
How is the high-voltage conductor of a four-wire, delta-connected system with the midpoint of 1-
phase grounded identified?
It should have an orange outer finish or be tagged clearly
On what is the capacity of a fuse panel based?
On the amperage rating of the panel’s bus bars
What is a dead front fuse panel?
A panel that has no live parts exposed when the door is open. The cover must be removed to gain access to the
interior parts.
What are three types of fuses used in fuse panels?
Plug fuse, cartridge fuse, and knife-blade fuse.
Explain the conditions under which an Edison-base fuse panel can be installed.
An Edison fuse panel can be installed only when it is modified by inserting adapters in the fuse holders to
accept type S plug fuses.
What is the main advantage of a circuit-breaker panel over a fuse panel?
When an overload occurs and trips the circuit breaker, the breaker can be reset to restore the circuit without
having to remove and replace it.
Why are breaker panels preferred over fuse panels?
Because circuit breakers can be reset after being tripped, while a blown fuse must be removed and replaced.
Circuit breakers can also be used as a switch to shut off the circuit
What is the basis upon which you select a panelboard for installation in a building?
The panelboard to be installed is determined by the size of the building and the equipment to be used in it.
Why do you leave unused spaces when you install a panelboard?
To provide for future expansion.
What usually determines whether we use a surface-mounted or flush mounted cabinet?
Exposed wiring or concealed wiring.
What are the space requirements for mounting panelboard cabinets in damp locations?
A 1/4-inch airspace must be provided
What is the procedure for installing a flush-mounted cabinet in a masonry wall?
The cabinet may be recessed in the wall with the front edge up to 1/4 inch from the finished surface. The cabinet
is attached to the wall with hollow wall fasteners or masonry anchors.
What action is required if you remove a cabinet knockout and then do not use it?
Close the hole with a plug or plate to provide protection similar to that provided by the original cabinet walls.
How do you protect No. 3 conductors from damage when you bring them into the cabinet from metal
conduits?
By use of insulated bushings on the end of the conduit
What is the general rule for determining the length of conductor ends brought into a panelboard
cabinet?
Cut the conductor ends at least long enough to allow any conductor to be connected at any point in the cabinet.
How do you attain electrical continuity between the equipment ground bar and the panelboard
cabinet?
By use of a bonding jumper between the bar and the cabinet or by running a screw through the bar into the
cabinet.
When do you bond the equipment ground bar and the neutral bar together?
When the panelboard is used as the service entrance equipment
How do we usually connect No. 12 conductors to a panelboard?
By looping them around a screw-type terminal (terminal loop
With what do we connect a No. 8 conductor to a panelboard?
A terminal lug.
What are pressure-type terminals used in panelboard cabinets to connect?
Large conductors, neutral conductors, and equipment grounding conductors.
How can you connect conductors to a panelboard to permit repositioning or repair if the conductor is
broken?
Run conductors beside the panelboard and then loop them back 180º before connecting them to fuses or circuit
breakers.
Where do most circuit breaker panelboards have the ungrounded conductors connected?
The breaker.
What factors influence the sequence for connecting conductors to a panelboard?
The arrangement of the bus bars in the panelboard, whether circuits are 240 or 120 volts, and the need to
balance the load.
What type of panelboard has all 240-volt circuits in one section and all 120-volt circuits in another
section?
Split bus.
What results when a panelboard is set up so that any two adjacent terminals provide 240-volt service?
Any two adjacent 120-volt circuits being connected to different phase conductor(s).
What is load balancing?
The process of equalizing the load on the supply conductors
What is the purpose of load balancing?
To prevent voltage drop from overloading one side of the incoming service and to prevent the possibility of
overloading the neutral.
What is the neutral load on a 240-volt, single-phase panel when A phase equals 65 amperes and B
phase equals 39 amperes?
The neutral load is the difference of A phase and B phase or 26 amperes
What are the A phase amperes on a 240-volt, single-phase panel when B phase equals 75 amperes and
the neutral equals 15 amperes?
The A phase amperes equal 75 ±15 amperes.
Name the two types of plug fuses.
Edison base and type S.
What are the limitations on using Edison-base fuses?
Edison-base plug fuses cannot exceed 30 amperes at 125 volts and can be used as replacements only.
List the amperage ratings for type S plug fuses.
0–15 amperes, 16–20 amperes, and 21–30 amperes.
What is the maximum capacity of amperes for ferrule-type cartridge fuses?
60 amperes.
Why can’t you use a 60-ampere, ferrule type in place of a 20-ampere, ferrule type?
Fuse diameter and length increase as amperage and voltage increase.
What must be the weakest part of an electrical circuit?
The fuse.
How does a thermal-type circuit breaker work to interrupt the circuit on an overload?
It contains a bimetallic strip that expands and moves when heated. Current flow causes heat when an overload
occurs. The heat developed expands the bimetallic strip until it trips the latch, opening the contact points,
thereby interrupting the circuit.
How does a magnetic type of circuit breaker open the circuit on an overload?
By use of an electromagnet.
What is the advantage of a magnetic circuit breaker over a thermal type?
It opens the circuit instantaneously when there is an excess of current flow.
What is the purpose of a GFCI?
A GFCI used as extra protection on circuits where the potential of having a ground though the user is higher
Where must ground fault breakers be installed in a home?
All 120-volt, single-phase, 15- and 20-ampere receptacles in bathrooms, garages, and outdoors.
What is a branch circuit?
A circuit installed between the final overcurrent device and the outlets for connecting electrically operated
equipment.
For what purpose are most panelboards furnished power by feeder circuits used?
Branch circuits.
What is the purpose of sub-feeders?
Sub-feeders serve the same purpose as feeders except they deliver power from a feeder-fed panelboard to
branch-circuit panelboards.
What are three advantages of using feeder circuits in a building instead of just having branch circuits?
Feeders reduce the voltage loss in the conductors and save material and labor.
What is the main objective when installing electrical circuits?
To keep troubles and hazards at a minimum consistent with existing conditions.
Which method do we commonly use for circuit installation when there is little chance of damage or
moisture contamination?
Nonmetallic cable.
Besides the method used in the preceding question, list three other general methods of installing
electrical circuits.
Metal raceways, rigid nonmetallic raceways, and cable trays.
What are the special installation requirements when a common neutral is used with two or more
feeder circuits to be installed in a metal raceway?
All the involved conductors must be put in the same raceway.
What measurement system is used by many foreign countries to determine wire size?
Square millimeters (sq mm.)
What do most overseas switches require?
A ground
What might you find inside a foreign male plug?
A fuse rated for the load of the cord.
With whom do you consult before working on foreign electrical systems for the first time?
Your supervisor, who will brief you on the many precautions you should take.
What is a blueprint?
A set of instructions on how to construct a building. It is a reproduction of a set of working drawings
List five of the drawings usually included in a set of blueprints.
The plot plan, exterior elevation, interior elevation, floor plan, and sectional or detail drawings.
What is included in a plot plan that would be helpful to an electrician?
The location of the service drop or service lateral and where it is to be connected.
Describe an exterior elevation.
It shows views of finished exterior walls along with finished gradelines and floorlines.
What type of information do interior elevations contain that would be helpful for installing outlets and
switches?
It shows where counters, sinks, and cupboards are going to go in kitchens and bathrooms, which helps in
determining where to put switches and receptacles
Which blueprint drawing shows the layout of all the walls and is most helpful to an electrician?
Floor plan.
If the scale of a drawing is 1/8 inch = 1 foot, what distance would a line 2 inches long represent?
16 feet.
What are the four basic types of electrical diagrams?
The block, schematic, connection and wiring diagram.
What are the three diagrams that show physical relationships of parts or components?
Block, wiring, and connection diagrams
What does the block diagram usually explain?
Power distribution systems.
Wiring diagrams often use pictures to show components. What often accompanies the wiring
diagram?
A replacement parts list.
What type of diagram shows the relative positions of the components and all the circuit connections?
The wiring and connection diagram.
What type of diagram makes it easy to trace the electrical operation?
The schematic diagram.
The simplest way to estimate the general lighting load requirements for a facility is to use
NEC® article 220–3. This article has a table that gives a volt-amp (VA) load per square foot of the facility
in question. The first thing to note is that you must compute the floor area from the outside dimensions of
the building.
Why must a conductor be provided free airspace in a box?
To prevent the buildup of heat in a box.
How do we determine the space available in a box?
By referencing table 370-16 in the NEC®.
What is the total volume of the box that results when you gang three switch boxes?
It is triple that of a single box
How do you determine whether a box is large enough for the number and size of conductors it
contains?
By consulting the table for boxes in the NEC®.
You have a device box 21/2 inches deep that lacks 3 cubic inches being large enough for the
conductors to be installed, and there is not enough space to use a deeper box. How can you provide
enough space and still use a device box?
You can remove one side of the box and install a space expander to replace the side
When wiring is done with nonmetallic boxes, how do you determine the size box needed at each
location?
You determine the free airspace requirements for each conductor by consulting the “Volume Requirements for
Each Conductor” table and then getting the box size by adding up the space requirements of all the installed
conductors and hardware
Determine the cubic inches required in a box for installing a duplex receptacle outlet using No. 10
nonmetallic cable with ground and anchored with a cable connector.
The equivalent number of conductors is four (two conductors, one equipment ground, and one device). No. 10
conductors require 21/2 cubic-inch space each: 4 × 21/2 = 10 cubic inches.
What is the main disadvantage in using screws to mount boxes that do not have brackets?
The side of the boxes must be removed before screws can be used to mount them.
Briefly describe the mounting procedure for an outlet box without mounting brackets when the wall is
to be covered with 1/2-inch sheetrock.
Drive nails through the holes near the bottom (or back) of the box and into the stud after the box is positioned to
project from the stud to allow for the sheetrock, using the depth markings on the box as a guide.
When you are to use nails for mounting a device box so the nails extend from side to side but are
outside the box, what type of mount do you use?
An S bracket mount.
In what cases is it advantageous to be able to drive nails through box brackets at a slant?
Where stud spacing is less than normal.
What is the difference in mounting procedures between a D bracket and an A bracket?
A D bracket is nailed to the side of the stud, while an A bracket is nailed to both the face and the side of the
stud.
When using A bracket box mounts, how do you allow for different thicknesses of wall-surfacing
materials?
You select the box according to the wall material thickness.
How do you mount a box with a B bracket?
Place the bracket over the face of the stud and drive the spurs in to hold the box in place while you drive the
retaining nails in place
A square box with a B bracket is installed for a receptacle outlet. What prevents the device cover with
its retaining screws from causing a bulge in the sheetrock?
The B bracket extends beyond the edge of the box enough to allow space for the device cover and screws to
prevent bulging the sheetrock
When using a box with a B bracket for switch installation, how do you make sure the switchplate will
not overlap the door trim?
By using a box with an extended B bracket to provide the needed space.
What type of box bracket do you use if conduit is to be brought through the mounting stud into the
box?
A J bracket
Why does an FH box bracket make a more rigid mount than an FA bracket?
The FH bracket has two barbed hooks that you drive into the face of the stud before you nail the bracket to the
side of the stud; the FA bracket you nail only to the side of the stud.
When do we use a box with a W bracket in preference to one with an FH bracket?
When the box is being mounted next to a door, to provide for clearance between the wide door trim and the
switch plate
Describe a quick and easy procedure for mounting a box on a metal stud.
An easy way is with a spring metal clip. Tap the clip onto the open edge of the box. Tip the box and clip so that
the upper prong slips behind the face of the stud. Press the lower prong of the clip back with your thumb until it
slips behind the stud face and locks the box in place. You can also attach them with sheet metal screws or
machine bolts and nuts.
A box has been mounted on a metal stud with a spring metal clip. You discover it is 4 inches too
high. What do you do?
Release the spring tension on the stud and move the box to the proper height.
Name four ways that you can mount boxes between ceiling joists.
Bar hangers, metal straps, made metal straps, or wooden strips
In what two ways can you attach boxes to a bar hanger?
By installing a fixture stud or a clamp through the knockout in the bottom of the box
How do you compensate for varying widths when you are installing boxes on bar hangers?
Bar hangers are adjustable so that you can adjust the length to the space as needed.
Describe the installation of a ceiling box between framing members using a wood support.
Cut a piece of 1 by 4 lumber to fit between the joists. Nail it to the joists at a level that allows for the depth of
the box plus the thickness of the ceiling material.
What are the height requirements for mounting boxes in a wall?
No specific height requirements exist. Boxes are mounted at a height that meets the needs for which they are
being installed
What are two disadvantages of having receptacle outlets mounted against the floor?
They are hard to use and may be hazardous when floors are being mopped.
What is the most popular height for mounting receptacle outlets in a house?
Twelve inches from the floorline to the center of the box.
Name three common devices we use to measure the height for mounting outlet boxes in the living
areas of a house
Marked hammer handle, rule, or notched stick.
Describe the procedure you use if the location of all boxes is to be laid out before mounting begins.
A lumber crayon, carpenter’s pencil, or felt-tip marker shows where boxes are to be mounted. Mark the location
of each box with an arrowhead on the face of the stud or other framing member. The point of the arrow shows
where the center box is to be mounted. Show the type of device to be installed with symbols, such as XX for
duplex receptacle, SS for two single-pole switches, S3 for a three-way switch, or XR for a range outlet.
List places where boxes normally are mounted 4 feet above the floorline.
Most switches and outlet boxes in laundry and utility rooms and garages.
When are switch boxes mounted above 4 feet high?
Usually when some type of wainscoting or paneling 4 feet high is to be used to finish the wall.
What is the normal height for outlet boxes over countertops?
Forty-four inches.
How do you use a tape to locate the centerpoint of a room for a ceiling light?
Find and mark the halfway point across one dimension of the room near the center. Make a similar measurement
on the other side of the center and mark the halfway point. Connect the two marks with a line. Measure the other
dimension of the room and mark the center on the preceding line. This point is the location for the ceiling light.
How can you locate the spot for a single ceiling light without using a tape?
Run diagonals with string from opposite corners of the room. The point of intersection is the center of the room
and the place for the box
What is a simple way of finding the box location when a room is to have two ceiling lights?
Measure half the length of the room along each wall and then run diagonals with string for each half. The
intersection of the diagonals is the place for the light boxes.
A room 25 feet long by 15 feet wide is to be lighted by a row of three lights down the center. How far
apart do you place adjacent lights? How far from the wall do you place the end light?
The space between lights equals 25 divided by 3, which is 81/3 feet or 8 feet 4 inches. The space from the wall
to the end lights is 8 feet 4 inches divided by 2, or 4 feet 2 inches.
Briefly describe the construction of nonmetallic sheathed cable.
Nonmetallic sheathed cable consists of two or three insulated conductors in an outer sheath of thermoplastic or
treated braid. It may have an added bare or insulated conductor to be used as an equipment ground.
What are two characteristics of the outer covering of nonmetallic cable?
It is flame retardant and moisture resistant.
Describe the conductors found in nonmetallic cable.
Conductors may be copper, aluminum, or copper-clad aluminum. Copper conductors range in size from No. 14
to No. 2 AWG, and aluminum and copper-clad aluminum from No. 12 to No. 2 AWG.
What markings do you normally find on nonmetallic cable?
Manufacturer’s name or trademark, maximum working voltage, wire size and number of conductors, whether it
has a ground, and the cable type
In what types of buildings may you install NM cable?
One- and two-family dwellings and other structures that are no more than three floors above grade.
Where in a building may you install type NM cable?
In either exposed or concealed work in usually dry locations (air voids in masonry block or internal tile walls)
or in areas that are not subject to excessive moisture or dampness.
How does NMC-type cable differ from NM-type cable?
Besides being flame retardant and moisture resistant, type NMC cable is fungus resistant and corrosion
resistant.
Where may you use type NMC cable?
In the same places as type NM cable, plus moist, damp, and corrosive locations. These locations include outside
masonry block and tile walls.
What sources of information does an electrician depend on when detailed wiring specifications for a
building are not furnished?
The NEC® and the electrician’s experience.
What principle does an electrician use as much as possible when routing circuits?
A straight line is the shortest distance between two points
Where are most circuits in a one-story residence?
Overhead, spread out across the ceiling area.
How far from a box or cabinet must you anchor cable?
12 inches.
How do we usually fasten concealed cable to framing members?
With staples
How do you fasten cable to joists in an attic?
On every second, or on each joist, depending on distance.
How do you fasten cable that runs parallel to the joists?
It is best to attach it to the side.
For how many feet from the scuttle hole must you use guard strips on cable?
Within 6 feet.
When exposed circuits are put in, how do you install cable?
To follow the surface of the building finish or installed on running boards.
Where do you attach cable on the stud when that cable is run to a box that is mounted flush with the
face of an open stud?
On the face of the stud.
How do you usually install cable on a finished surface?
With cable straps.
What is the difference between a cable anchor for a cable with three No. 8 conductors and one for a
cable with two No. 12 conductors?
A round cable strap is used for a cable with three No. 8 conductors, while an oval cable strap is used for one
with two No. 12 conductors
When making bends in nonmetallic cable, what must be the size of the radius of the bend?
Not less than five times the cable’s diameter.
What is the least protection required for exposed cable that passes through a floor?
At least 6 inches above floor level.
What action is required where exposed cable on a wall may be vulnerable to physical damage?
It should be protected with conduit, pipe, or guard strips.
What is meant by concealed wiring?
Wiring installed between floors and ceilings of multi-level buildings, in the ceilings of finished basements, and
in the walls of buildings. It is not visible or easily accessible after the building is finished.
What does wooden framing require to install concealed wiring?
Bored holes or notches.
What size bit do you usually use to install concealed lighting and outlet circuits in a building?
From 5/8 to 3/4 inch in diameter.
Why is it particularly undesirable to drill cable holes in 2 by 4 studs at any angle other than
horizontally?
Holes on an angle in studs do not provide a minimum side protection of 11/4 inches for the cable, thereby
requiring use of metal sleeves or plates
How do you install concealed cable when metal studs are used?
The same way you do in wood studs
What actions do you take between the time the distribution panel is installed and the start of cable
installation when circuits are being installed?
Mark the location of outlet boxes, mount the boxes in place, and bore the holes or cut notches in framing
members.
Describe the cable that is usually used for installing branch circuits and the way in which it is
packaged.
12/2 with ground and comes as a 250-foot coil in a carton.
How do you remove cable from its carton?
Grasp the end of the cable d through the hole in the top of the carton and pull it out. Since the cable comes out
as a spiral, you must uncoil it before you use it.
What happens if you try to use cable without uncoiling it?
It develops sharp kinks that damage the insulation and prevent its being pulled through bored holes.
What is the procedure for installing the free end of the cable in an outlet box?
Start by stripping 6 inches of the outside covering from the cable end. Remove one of the box pry-outs and
insert the cable end through the hole and under the clamp until one-quarter of an inch of the cable cover extends
through the clamp. Tighten the clamp to hold cable firmly in place.
What is the purpose of providing 6 inches of conductor inside an outlet box?
This amount of conductor is needed to make splices or to attach devices or fixtures easily.
How does the procedure for installing cable in a box differ from that previously used when the box
does not have cable clamps?
A knockout must be removed from the box and a cable connector installed to provide a means of anchoring the
cable to the box.
How do you install cable in a nonmetallic box that does not have clamps?
Punch the hole out of the box, strip 6 inches of the cable cover, insert the cable through the box hole to expose
one-quarter inch of cable cover inside the box, and anchor the cable within 8 inches of the box.
What is the procedure for getting cable installed between outlet boxes?
Anchor the cable to within 12 inches of the box to which the free end is attached, and then run the cable along
the framing members and fasten it at least every 41/2 feet until it reaches the other box.
When cutting cable to length for attachment to a box, what must you allow?
Six inches of free conductor in the box.
What do you do before you start to run cable when holes through framing members are involved?
Take a look at where the holes are located and then decide where to start for the easiest installation and least
waste.
State two reasons for making splices in an interior electrical system.
Splices are used to connect wires together to form complete circuits and to connect or add ground wires so that
all metal units in the electrical circuits are grounded.
What two requirements must a splice meet?
Must be both mechanically and electrically secure.
What is the preferred splice to use in interior wiring?
Solderless pigtails, or wire nut splices.
On small conductors, what is the easiest method of removing the insulation for making a splice?
With a wire stripper.
What is the main disadvantage of removing insulation with a stripper?
It is easy to nick the wire, which may cause it to break.
What do you use to remove insulation from a No. 8 AWG conductor?
A knife.
How do you remove insulation from the end of a wire with a knife?
Start by cutting the insulation at an angle of about 30°. Remove the insulation the same way you sharpen a
pencil, being careful not to cut the wire.
What action is required if the end of a bare wire is covered with oxidation?
Use the knife blade to scrape the wire until it is clean.
What material do you normally use to insulate a soldered pigtail splice?
Plastic electrical tape.
How many layers of tape are required for a well-insulated splice?
4
What is the advantage of having a tape that stretches when you insulate a splice?
It allows the tape to be applied so that a close, smooth wrap is formed. By varying the tension, you can stretch
the tape to conform to angle and diameter changes and ensure a snug fit.
How do you apply tape to a splice to ensure adequate coverage without going over it several times?
Apply the tape smoothly, half lapping each turn of the tape until you reach the end of the splice. At the end, fold
the tap over and then bring it back toward the starting point, half lapping each wrap of the tape.
How do you make a solderless pigtail splice?
Remove the insulation from the ends of the wires and twist them together three turns. Finish the splice by
installing a wire nut and tightening it.
If someone asked you for a blue wire nut, would you have enough information to make the correct
choice? If not, why not?
No; because color alone does not indicate the size of a wire nut.
What two items are needed to make a compression splice?
A splicing sleeve and a special crimping tool.
What is the purpose of a noninsulated sleeve?
To splice several grounding conductors together.
What kind of splice do you make with an insulated sleeve that has one closed end?
A crimped pigtail
What are the two methods you use for connecting the equipment ground to a box?
By using a grounding clip or a screw that is not used for any other purpose.
What grounding requirement must you meet when connecting more than one receptacle in a circuit?
Continuity of the equipment ground must not be broken when a receptacle is removed from the circuit.
What two situations do not require using a grounding jumper on a receptacle?
Surface-mounted boxes where there is direct contact between the yoke of the receptacle and the box and any
box where receptacles designed specifically to provide metal-to-metal contact between the yoke and the box are
used.
On a duplex receptacle, which screw connects the equipment ground?
Green hexhead
What are three reasons for making sure that terminal connections are mechanically and electrically
secure?
To ensure good circuit operation, prevent fire, and personnel safety.
What type of terminal connection do you use most often on devices and fixtures?
Terminal loop and screw.
What is the first step in making a terminal loop?
Strip approximately 3/4 inch of insulation from the end of the conductor.
What tool do you use to make a terminal loop?
Needlenose or longnose pliers.
Why must you place a terminal loop around the screw in a clockwise direction?
So that tightening of the screw does not spread the loop.
How do you make terminal connections on fixtures that have stranded fixture wires already attached?
Circuit wires are pigtailed to the fixture wires with a wire nut.
To which terminal screw do you connect the ungrounded conductor when connecting a receptacle or
fixture?
Brass or dark colored screw.
Which conductor do you connect to the silver terminal of a receptacle or fixture?
Neutral or grounded conductor.
What size screws do you use to mount a receptacle or switch to a box?
7/8 inch, 6–32.
What is the maximum weight fixture that can be supported from an outlet box?
50 pounds
What size screws do you use to mount a fixture directly to an outlet box?
8-32
How far must you mount an unwired recessed fixture from the outlet or junction box?
1 foot
What type of wire must you run to an unwired recessed light fixture?
Heat Resistant
How do you mount recessed fixtures?
Between ceiling joists with special bar hangers
What are the minimum and maximum lengths of flexible conduit (or any other suitable raceway) that
can be run to a recessed fixture?
Eighteen inch minimum and 6 feet maximum
Name three fastening devices you can use to mount a fixture directly to a ceiling.
Any three of these are correct; Wood screws, hollow wall anchors, toggle bolts, or lead anchors.
When can you use wood screws to fasten a fixture directly to a sheetrock ceiling?
When the mounting holes of the fixture line up with the wood ceiling joints
How can you mount an unusually heavy fixture directly to a sheetrock ceiling?
By using wood strips between the toggle and the sheetrock.
What type of fasteners do you use to mount a fixture to a concrete ceiling?
Lead anchors.
What are the purposes for covering devices and fixtures?
To provide a neat appearance, protect the conductors, and prevent shock.
What size and how many screws are needed to attach a flat cover plate to a receptacle?
One, 3/8-inch, 6–32 screw.
