Questions 26-28 COPY Flashcards
(127 cards)
1
Q
- Why is nonmetallic-sheathed cable popular in residential wiring?
A
Nonmetallic-sheathed cable is very popular in residential wiring because it is inexpensive and easy to install.
2
Q
- What do the two numbers marked on nonmetallic-sheathed cable indicate?
A
The numbers provide information about the size of the wire and the number of conductors in the cable.
3
Q
- Differentiate between type NM and type NMC cable.
A
Type NM cable is a nonmetallic-sheathed cable that has conductors within a nonmetallic jacket and is typically used for dry interior wiring. Type NMC cable is a nonmetallic-sheathed cable that has the conductors enclosed within a corrosion resistant, nonmetallic jacket.
4
Q
- How is non-metallic -sheathed cable prepared?
A
Typically the cable must be cut to length, have the outer jacket removed to a distance from the end, and have a specified amount of insulation removed from the individual conductors.
5
Q
- What does rough-in mean in regard to electrical installations?
A
Rough-in is the placement of electrical boxes and wires before wall coverings and ceilings are installed.
6
Q
- Define receptacle box.
A
An electrical device designed to house electrical components and protect wiring connections.
7
Q
- Where and how are receptacle boxes for NM cable installed?
A
Receptacle boxes and junction boxes must be installed at every point in the electrical system where NM cable is spliced or terminated. Receptacle boxes are installed so that every point in the system is accessible for future repairs or additions. Boxes must be completely covered to the point that a box becomes inaccessible.
8
Q
- What are uses of the different types of receptacle boxes used in residential wiring?
A
Octagonal boxes are typically used in ceilings for lighting fixtures. Square and rectangular boxes are used for switches and receptacles. Any of the three are used for junction boxes.
9
Q
- Define knockout.
A
A knockout is a round indentation punched into the metal of a box and held in place by unpunched narrow strips of metal.
10
Q
- Why is cable stripped before being installed in a box?
A
Stripping the wire before installing the wire into a box saves time later when outlets and switches are being installed.
11
Q
- Explain two methods of routing cables through solid corners.
A
Cables are routed through solid corners by using various methods. One method is to drill holes from each side at an angle to accommodate a cable run. Drilling holes from each side will save wire but may be time-consuming if the holes do not line up properly. Another method is to notch the corner studs, using steel plates for protection.
12
Q
- At what intervals must NM and NMC cable be supported or secured?
A
NM and NMC cable must be supported or secured (stapled) every 4 ½ of cable run and within 12” of a box.
13
Q
- Compare the three methods of residential grounding.
A
- Component grounding – is a grounding method where the ground wire is attached directly to an electrical component such as a receptacle. Component grounding requires that the ground wire be attached before the electrical component is permanently mounted.
b. Pigtail grounding – is a grounding method where two ground wires are used to connect an electrical device to a ground screw in the box and then to system ground. The box ground ire is secured to a threaded hole in the bottom of the box. Once secured, the cable ground wire is pigtailed to the box ground wire.
c. Clip grounding is a grounding method where a ground clip is slipped over the ground wire from the electrical device. The ground wire and ground clip are secured with pressure using a screwdriver.
14
Q
- How are cables secured to outlet boxes?
A
Cables are secured to outlet boxes by clamps. The three types of clamps typically available for nonmetallic cables are saddle, straight, and cable connectors.
15
Q
- Why would metallic-sheathed cable be used rather than nonmetallic-sheathed cable?
A
Metallic sheathed cable is often used instead of nonmetallic cable because it protect wires with it’s metal protective covering.
16
Q
- Define bonding wire.
A
A bonding wire is an uninsulated conductor in armored cable that is used for grounding. The bonding wire is in contact with the flexible metal outer jacket to assure proper conducting (ground) path along the entire length of an armored cable.
17
Q
- Identify the applications of the three types of armored cable the NEC recognizes for residential work.
A
The NEC recognizes three types of armored cable for residential work: AC, ACT, and ACL. AC and ACT armored cables are used in dry locations. Both AC and ACT may be finished through the air voids of masonry walls when the walls are not exposed to excessive moisture. Both AC and ACT may be used for under-plaster electrical extensions. ACT armored cable is used for either exposed work or concealed work. ACL armored cable is embedded in concrete or masonry, run underground, or used where gasoline or oil is present. ACL armored cable is lead-covered to provide additional protection for masonry and underground applications.
18
Q
- Describe the method used to cut through the metal jacket of armored cable.
A
The first step is to cut through the outer armor (one of the convolutions) at a 45 degree angle about 6” to 8” from an end. To prevent damage to the insulation of conductors, care must be taken not to cut too deeply into the jacket of the cable. When the armored cable is cut, the cable is separated by twisting the two sections apart. The armored cable must be carefully flexed until the cable breaks. Twisting the cable can open the convolutions enough so that tin snips or cable cutters can be inserted.
19
Q
- What is the purpose of an anti-short bushing?
A
An anti-short bushing is a plastic or heavy fiber paper device used to protect conductors of armored cable. The bushing covers the sharp edges at the ends of the armor to reduce the possibility of damage to conductor insulation.
20
Q
- How is armored cable roughed-in into studded walls?
A
When roughing-in armored cable into studded walls, the cable must be pulled into position first and then cut to length. Pulling the armored cable into position then cutting length, reduces waste.
21
Q
- What is the minimum bend radius used to prevent breaking armored cable?
A
The minimum bend radius used to prevent breaking armored cable is 90 degrees. At least five times the diameter of the wire.
22
Q
- What is a conduit?
A
Conduit is a rugged protective tube typically metal, through which insulated conductors are pulled.
23
Q
- List and define the three most common types of conduit.
A
Electrical metallic tubbing, ridged metal conduit, and flexible metal conduit are primarily used in residential. Electrical metallic tubbing is a light-glued electrical pipe often referred to as thin-wall conduit. Rigid metal conduit is a heavy-duty pipe that is threaded on the ends much like standard plumbing pipe. Flexible metal conduit is a conduit that has no wires and can be bent by hand. The conductor’s wires are not installed until the system is complete.
24
Q
- What is a deburring?
A
It is the process of removing the rough edges off of conduit. It is called deburring, and is accomplished with a conduit deburring tool designed for this purpose.
25
25. How is a 45 degree bend made in conduit?
To create a 45 degree bend, a hand bender is placed on EMT conduit. The handle of the bender is raised until the handle is in the vertical position. The handle is pulled until the angle required 45 degrees is completed.
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26. Define offset.
An offset is a compound bend in conduit used to bypass many types of obstructions.
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27. Describe the different types of conduit connectors.
A compression connector is a box fitting that firmly secures conduit to a box by utilizing a nut that compresses a tapered metal ring (ferrule) into the conduit. As the compression nut is tightened, the nut forces the ferrule into the conduit, locking the conduit in position. An indenter connector is a box fitting that secures conduit to a box with the use of a special conduit to a box with the use of a special indenting tool. Lastly a set screw connector is a box fitting that relies on the pressure of a screw against the conduit in place. Set screw connectors are also reusable.
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28. How is conduit joined together?
Conduit couplings are used to join conduit together.
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29. How is rigid metal conduit used in residential construction?
Typically for residences ridged metal conduit is only used for overhead service risers and for underground services.
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30. Define fishing.
Fishing is the term used for the process of pulling wires through conduit. The fish tape is extended and pushed through the conduit until the tape reaches an opening. At the opening the wires being installed are firmly secured to the fish tape. The fish tape is retrieved by pulling the tape out of the conduit with wires attached.
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1. What is a service entrance?
A service entrance is the link between a residence and the power company. Service entrances provide all the equipment necessary to obtain electricity and distribute it throughout a residence.
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2. List three tips for determining the placement of a service entrance.
1. Keep the service wires as short as possible.
2. Locate the service panel as close to the kitchen as possible to prevent costly wire runs to major appliances.
3. Do not place the meter socket on the outside of a bedroom wall.
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3. How are the residential service entrances typically rated?
Service entrances for single family dwellings require a minimum 100 A capability. For larger residences and structures using electric heat, a 200 A or larger service entrance can be required.
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4. List the different types of service entrances.
Service entrances may be overhead riser, lateral (conduit), lateral (cabinet), and mobile home service entrances.
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5. What are the benefits of using lateral service entrances as opposed to overhead riser service entrances?
A lateral service entrance (conduit) has all service wires buried underground, creating a condition where the wires are subjected to less damage from the environment and allowing unsightly poles and service wires to be removed from streets and alleys.
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6. Describe how to secure service equipment.
| Meter sockets and service panels must be firmly secured before any wires (cables) are pulled or conduit attached.
When service equipment is mounted on wood, wood screws or lag bolts are used to hold the equipment in place. When service equipment is mounted to masonry, drills and special bolts with anchors are used. Plastic anchors support a considerable amount of weight when properly installed.
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7. What colors of wires are used for electrical wiring in a residence and what is indicated by each color?
Red, black, and white wires for the service panel enter the residence through a service head. The red and black wires represent the hot or live wires, and the white wire represents the neutral.
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8. What is the purpose of bus bars?
Bus bars distribute the power to the circuit breakers in an organized manner.
39
9. Define service drop.
A service drop consists of overhead wires and devices that connect the power company power lines to a residence. Service drops are owned and maintained by the service company.
40
10. Describe the NEC standards governing the elevation of service conductors.
To comply with NEC standards, a service head must be at least 10’ above and 3’ to the side of any platform. Service conductors must be at least 3’ from the bottom and sides of the window. Nec standards governing the elevation of service conductors specify a 3’ clearance over adjacent buildings. Sidewalks require a 10’ minimum clearance. Private drives require a 12’ minimum clearance. Alleys and streets require an 18’ minimum clearance.
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11. Define service lateral.
Is any service to a residence that is achieved by burying the wires underground.
42
12. List the types of service laterals used for residences.
a. From utility manhole in street to service panel disconnect.
b. From utility sidewalk handhole to service panel disconnect.
c. From pole riser to service panel disconnect.
d. From transformer pad to service panel disconnect.
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13. What is installed when trimming out or finishing a service entrance?
Insultation of service conductors, and branch wires.
44
14. Define generator.
A generator is an electromechanical device that converts mechanical energy into electrical energy by means of electromagnetic induction. AC generators (alternators) convert mechanical energy into AC voltage and current.
45
15. Define main components of an AC generator.
AC generators consist of field windings, an armature, slip rings, and brushes.
46
16. What is the major difference between AC and DC generators?
The major difference between AC and DC generators is that DC generators contain a commutator that reverses the connections to the brushes every half cycle. The commutator maintains a constant polarity of voltage to the load. AC generators use slip rings to connect the armature to the external circuit (load). The slip rings do not reverse the polarity of the output voltage produced by the generator. The result is an alternating sine wave output.
47
17. How are standby generators powered?
Stand by generators are powered by gasoline, natural gas, or LPG.
48
18. How is voltage calculated?
Voltage x Amps = Watts
49
19. Explain how to read an electric meter.
An electric meter has four dials. Each dial has a hand. Electric meters have two dials that read clockwise and two dials that read counterclockwise. To read a meter, always use the number that the hand has just passed (CW or CCW) on each of the dials.
50
20. What is an automatic transfer switch?
An automatic transfer switch is an electrical device that transfers the load of a residence from public utility circuits to the output of a standby generator during a power failure.
51
21. Where is an automatic transfer switch installed?
An ATS is installed in close proximity to the electrical distribution panel and should be installed by a licensed electrician.
52
22. What is rated voltage?
Rated voltage is a voltage range that is typically within plus or minus 10 percent of ideal voltage. Today, however, with many components derated to save energy and operating cost, the range is typically plus 5% to -10%.
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23. Why is voltage range used when rating electrical and electronic equipment?
A voltage range is used because an overvoltage is more damaging than an undervoltage.
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24. What are the different types of voltage changes in an electrical system?
A momentary power interruption, A temporary power interruption, A sustained power interruption
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A momentary power interruption –
is a decrease to 0 V on one or more power lines lasting from 0.5 cycles up to 3 sec. All power distribution systems has momentary power interruptions during normal operation.
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A temporary power interruption
is a decrease to 0 V on one or more power lines lasting between 3 sec and 1 min. Automatic circuit breakers and other circuit protection equipment protect all power distribution systems.
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A sustained power interruption
is a decrease to 0 V on all power lines for a period of more than 1 min. All power distribution systems have a complete loss of power at sometime.
58
25. What is a monetary power interruption?
A momentary power interruption – is a decrease to 0 V on one or more power lines lasting from 0.5 cycles up to 3 sec. All power distribution systems has momentary power interruptions during normal operation.
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26. Define open circuit transition switching.
Open circuit transition switching is a process in which power is momentarily disconnected when switching a circuit from one voltage supply level to another.
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27. Identify common causes of sustained power interruptions.
Sustained power interruptions are commonly the result of storms, tripped circuit breakers, blown fuses, and/or damaged equipment.
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28. What is the purpose of an uninterruptible power system (UPS)?
Is a power supply that provides constant on-line power when the primary supply is interrupted. For long-term power interruption protection, a generator/UPS is used. For short-term power interruptions, a static UPS is used.
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29. Define transit.
A transient is a temporary, unwanted voltage in an electrical circuit. Transient voltages are typically large erratic voltages, or spikes that have a short duration and a short rise time.
63
30. How can equipment be protected from transients?
A surge suppressor is a receptacle that provides protection from high-level transients by limiting the level of voltage allowed downstream from the surge suppressor.
64
1. What are some of the ways magnetism is utilized?
Magnetism is used to produce most of the electricity consumed, develop rotary motion in motors, and develop linear motion in solenoids.
65
2. Where is magnetic flux the strongest and why?
Flux is most dense at the ends of a magnet. For this reason, the magnetic force is strongest at the ends of the magnet.
66
3. What is solenoid and how is it used?
A solenoid is a device that converts electrical energy into a linear, mechanical force. Solenoids produce a linear, mechanical force when electricity is applied to the coil.
67
4. Which electromagnetic principle provides the basis for transformer operation?
The electromagnetic principle of mutual induction states that when the magnetic flux lines from one expanding and contracting magnetic field cut the windings of a second coil, a voltage is introduced in the second coil. The amount of voltage introduced in the second coil depends on the relative position of the two coils and the number of turns in each coil.
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5. Explain the difference between a step-up transformer and a step-down transformer.
A step-up transformer is a transformer in which the secondary coil has more turns of wire than the primary coil. A step-up transformer produces higher voltage on the secondary coil that the voltage applied to the primary. A step-down transformer is a transformer in which the secondary coil has fewer turns of wire than the primary coil. A step-down transformer produces a lower voltage on the secondary coil than the voltage applied in the primary.
69
6. How are transformers rated?
Transformers are rated by their volt-amphere (VA) or kilovolt-amphere (kVA) output. Small transformers are rated in either VA or kVA. Large transformers are rated in kVA.
70
7. Describe the different types of power loss that occur in transformers.
a. Hysteresis loss occurs every half-cycle of AC when the current reverses direction and some magnetism remains in the iron core.
b. Eddy-Current loss is caused by the induced currents that are produced in mental parts that are being magnetized.
c. Copper loss is caused by the resistance of the copper wire to the flow of the current.
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8. List the basic types of transformers.
The basic types of transformers include appliance/equipment, control, bell/chime, instrument (current), distribution, isolation, neon sign, and power transformers.
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9. What is the limiting factor in transformer loading and why?
Temperature is the limiting factor in transformer loading.
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10. When does a transformer become overloaded?
A transformer is overloaded when it is required to deliver more power than its rating.
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11. Compare the different transformer cooling methods.
a. Self-air cooled transformers – are transformers that dissipate heat through the air surrounding the transformer. Heat produced in the windings and core is dissipated into the surrounding air by convection. Convection heat transfer is increased by adding radiating fins to the transfer.
b. Forced-air cooled transformers are transformers that use a fan to move air over the transformer. Using a fan to speed the convection process increases the power that the transformer can deliver by about 30 percent over the power that can be delivered without a fan. Multiple high velocity fans are used in some applications to increase the transformer power output by more than 30 percent. The fans maybe designed to remain ON at all times or may be automatically turned ON when the transformer reaches a set temperature.
c. Liquid-immersed/self-air cooled transformers – are transformers that use refined oil to help cool refined oil or synthetic oil to help cool the transformers windings. The transformer coils and core are enclosed in a metal tank which is immersed in the oil. The oil is used to conduct heat from the windings and core to the outer surface of the transformer. The oil helps slow the heating process by increasing the heat storage capacity of the transformer.
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are transformers that dissipate heat through the air surrounding the transformer. Heat produced in the windings and core is dissipated into the surrounding air by convection. Convection heat transfer is increased by adding radiating fins to the transfer.
Self-air cooled transformers
76
are transformers that use a fan to move air over the transformer. Using a fan to speed the convection process increases the power that the transformer can deliver by about 30 percent over the power that can be delivered without a fan. Multiple high velocity fans are used in some applications to increase the transformer power output by more than 30 percent. The fans maybe designed to remain ON at all times or may be automatically turned ON when the transformer reaches a set temperature.
Forced-air cooled transformers
77
are transformers that use refined oil to help cool refined oil or synthetic oil to help cool the transformers windings. The transformer coils and core are enclosed in a metal tank which is immersed in the oil. The oil is used to conduct heat from the windings and core to the outer surface of the transformer. The oil helps slow the heating process by increasing the heat storage capacity of the transformer.
Liquid-immersed/self-air cooled transformers
78
12. Explain how to size 3 transformer.
a. Determine the total voltage required by the loads if more than one load is connected. The secondary side of the transformer must have a rating equal to the voltage of the loads.
b. Determine the amperage rating or kVA capacity required by the load(s). Add all loads that are (or may be) ON concurrently.
c. Check the frequency of the load(s) or nameplate. The frequency of the supply voltage and the electrical supply voltage and the electrical load(s) must be the same.
d. Determine the type of 3 voltage available. This includes three-wire no ground or three-wire no ground or three-wire with ground (four wire).
e. Check the supply voltage to the primary side of the transformer.
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13. How is transformer current draw calculated?
I = kVA cap X 1000/E
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14. What is transformer normal ambient temperature?
Transformer normal ambient temperature is 40 degrees C.
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15. How is a transformer derated when the maximum temperature exceeds the average temperature by more than 10 degrees C?
A transformer is derated by 1 ½ percent for each 1 degree C above 40 degree C when the maximum ambient temperature exceeds 10 degrees C above the average temperature.
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16. Describe delta transformer connection.
A delta configuration is a transformer connection that has each transformer coil connected end to end to form a closed loop.
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17. What is the advantage of a delta-to-delta transformer connection?
The advantage of a delta-to-delta connection is that if one transformer is disabled, the other two may be used in an open-delta connection for emergency power.
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18. What does it mean to balance the loads of a transformer?
The loads connected to a transformer should be connected so that each coil of the transformer carries the same amount of current for the various loads, such as for several motors.
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19. Describe the purpose of transformer taps.
Transformer taps are connecting points that are provided along the transformer coil. Taps are available on some transformers to correct for excessively high or low voltage conditions. The taps are located on the primary side of the transformer. Standard taps are provided for 2% and 5% of rated primary voltage.
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20. What conditions must be met before a single-phase transformer can be connected parallel?
a. Primary and secondary voltage ratings are identical.
b. Frequencies are the same
c. Tap settings are identical.
d. Impedance of either transformer is within plus or minus 7% (93% to 107%) of the other.
87
is a conduit that has no wires and can be bent by hand. The conductor’s wires are not installed until the system is complete.
Flexible metal conduit
88
is a box fitting that firmly secures conduit to a box by utilizing a nut that compresses a tapered metal ring (ferrule) into the conduit. As the compression nut is tightened, the nut forces the ferrule into the conduit, locking the conduit in position.
A compression connector
89
is a heavy-duty pipe that is threaded on the ends much like standard plumbing pipe.
Rigid metal conduit
90
is a light-glued electrical pipe often referred to as thin-wall conduit.
Electrical metallic tubbing
91
is a box fitting that secures conduit to a box with the use of a special conduit to a box with the use of a special indenting tool.
An indenter connector
92
is a box fitting that relies on the pressure of a screw against the conduit in place. Set screw connectors are also reusable.
set screw connector
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occurs every half-cycle of AC when the current reverses direction and some magnetism remains in the iron core.
Hysteresis loss
94
is caused by the resistance of the copper wire to the flow of the current.
Copper loss
95
is caused by the induced currents that are produced in mental parts that are being magnetized.
Eddy-Current loss
96
are transformers that use refined oil to help cool refined oil or synthetic oil to help cool the transformers windings. The transformer coils and core are enclosed in a metal tank which is immersed in the oil. The oil is used to conduct heat from the windings and core to the outer surface of the transformer. The oil helps slow the heating process by increasing the heat storage capacity of the transformer.
Liquid-immersed/self-air cooled transformers
97
are transformers that use a fan to move air over the transformer. Using a fan to speed the convection process increases the power that the transformer can deliver by about 30 percent over the power that can be delivered without a fan. Multiple high velocity fans are used in some applications to increase the transformer power output by more than 30 percent. The fans maybe designed to remain ON at all times or may be automatically turned ON when the transformer reaches a set temperature.
Forced-air cooled transformers
98
are transformers that dissipate heat through the air surrounding the transformer. Heat produced in the windings and core is dissipated into the surrounding air by convection. Convection heat transfer is increased by adding radiating fins to the transfer.
Self-air cooled transformers
99
Residential service entrances are typically rated in ampere because voltage is typically a standard ________.
(115/230 V)
100
A ________ utilizes a cabinet that encloses the service wires, meter socket, and meter.
Lateral service entrances (cabinet)
101
Whenever possible, large knockouts should be removed before the ________.
the service panel is mounted to reduce the risk of loosening the panel.
102
The electric power brought to a residence is typically a ___________.
115V/230 V 1 system .
103
The 115 V and 230 V voltages are ____ throughout the meter socket and into the service panel.
constant
104
Service Panel ________ convey power to single-pole and double-pole circuit breakers to form 115V and 230V circuits.
bus bars
105
Any single circuit breaker can only furnish power to _______.
one 115 V circuit
106
Two consecutive circuit breakers are used for a _____.
230 V circuit
107
The circuit breakers in a 230 V circuit must be consecutive why?
So that the breaker handles can be fastened together as one unit.
108
______ ensures that in the event of a 230 V overload, both hot lines disconnected simultaneously.
Fastening the handles together as one unit.
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Circuit breakers are snapped into position when being installed to the _____ of a service panel.
Bus bars
110
Are shaped to accept oval service cables. The sill plate covers the cable and the cable opening where the service enters the dwelling.
Service entrance caps
111
______ the cable and the cable and cable opening where the service enters the dwelling.
The sill plate covers
112
____ is applied to make the sill plate water tight.
Sealing compound
113
Service cable connector are available as _______ or as _________ when used to secure service cables in place.
standard box connectors, or watertight connectors
114
When a pole riser is used, the service installation is shared by the _____ and _______.
homeowner and utility company.
115
In many instances what is the electricians job when dealing with a pole riser.
Simply install conduit to a point at least 8' above grade and pull enough wire to reach the crossarm at the pole.
116
Require the homeowner to furnish a ______ in addtion to the regular electrical equipment. The utility company typically creates the trench from the ___ to the dwelling, buries the cable, and makes the final connections.
Transformer Pad
| transformer Pad
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Are magnets used to produce the magnetic field in a generator. The magnetic field in a generator can be permenent magnets or electromagnets. Most generators use electromagnets, which must be supplied with current.
Field windings
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Is the movable coil of wire in a generator that rotates through the magnetic field. The armature may consist of many coils. The ends of the coils are connected to slip rings.
Armature
119
Are metallic rings connected to the ends of the armature and are used to connect the induced voltage to the generator brushes. When the armature is rotated in the magnetic field, a voltage is generated in each half of the armature coil.
Slip rings
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Is the sliding contact that rides against the slip rings and is used to connect the armature to the external circuit (power grid).
brush
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As the armature is rotated, each half cuts across the magnetic lines of force at _________.
the same speed
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The strength of the voltage induced in one side of the armature is always ______ as the strength of the voltage induced in the other side of the armature.
the same
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Since the two halves of the coil are connected in a closed loop, the voltages add to each other. The result is that the total voltage of a full rotation of armature _______ the voltage of each coil half.
twice
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The _____ is obtained at the brushes connected to the slip rings, and is applied to an ____.
total voltage, external grid
125
Typical home emergency standby generators range in capacity from ______ to _______.
6500W to 40,000W
126
An _____ prevents electricity from flowing into the public service line sand accidentally injuring electrical company workers.
ATS
127
Is a transformer connection that has one end of each transformer coil connected together. The remaining end of each coil is connected to the incoming power lines (primary side) or used to supply power to the load(s) (secondary side).
Wye configuration
