Mike Holt: Unit 6 Conductor Sizing and Protection Calculations
What's the minimum size THHN conductor required for a 150A circuit breaker or fuse?
1/0 AWG
Feeder grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at _____ percent of the continuous and noncontinuous load.
100 %
The branch-circuit overcurrent device and conductors for fixed storage-type water heaters that have a capacity of 120 gal or less shall be sized not smaller than _____ percent of the rating of the water heater.
125 %
The minimum feeder conductor ampacity shall be no less than the noncontinuous load plus _____ percent of the continuous load, and not less than the maximum load after the application of adjustment and correction factors.
125 %
What's the ampacity of 1/0 THHN conductors when there are four current-carrying conductors installed in a raceway in a dry location?
136A
What size branch circuit is required for a 2,500W, 240V water heater?
15A
Overcurrent protection shall not exceed _____.
15A for 14 AWG copper, 20A for 12 AWG copper, or 30A for 10 AWG copper
What's the ampacity of 10 THHN conductors if there are thirty-one conductors in the cross-sectional area of a wireway?
16A
If a branch circuit supplies a single nonmotor-operated appliance, the rating of overcurrent protection shall not exceed _____ if the overcurrent protection rating is not marked and the appliance is rated 13.30A or less.
20A
What's the ampacity of 10 THHN conductors when there are eight current-carrying conductors installed in the same raceway in a dry location and the ambient temperature is 100°F?
25A
Which of the following is(are) a standard size for circuit breakers and fuses?
25A 90A 350A
What size conductor is required for a 70A breaker that supplies a 65A noncontinuous load?
4 AWG
What size conductor and overcurrent device are required for a 7,500W, 240V fixed electric space heater that has a 3A blower motor with 75°C terminals?
45A overcurrent device and an 8 AWG conductor
Overcurrent protective devices must be designed and rated to clear fault current and must have an adequate short-circuit interrupting rating for the available fault levels. If the minimum interruption rating isn\'t marked on the overcurrent protective device, according to the NEC the minimum for circuit breakers is _____ and _____ for fuses.
5,000A, 10,000A
Where six current-carrying conductors are run in the same conduit or cable, the ampacity of each conductor shall be lowered to _____ percent of its ampacity.
80 %
The ampacity adjustment factors of Table 310.15(C)(1)) do not apply to Type AC or Type MC cable without an overall outer jacket, if which of the following condition(s) is(are) met.
Each cable has not more than three current-carrying conductors. The conductors are 12 AWG copper. No more than 20 current-carrying conductors are installed without maintaining spacing.
Which of the following describes Type TFN insulation?
Solid or flexible stranded fixture wire having a thermoplastic insulation with a nylon outer cover
One of the purposes of conductor overcurrent protection is to protect the conductors against excessive or dangerous heat.
TRUE
Type _____ insulated conductors shall not be subject to ampacity adjustment where installed exposed to direct sunlight on a rooftop.
XHHW-2
Conductor overload protection shall not be required where the interruption of the _____ would create a hazard, such as in a material-handling magnet circuit or fire pump circuit. However, short-circuit protection is required.
circuit
Where a portion of a feeder is connected at both its supply and load ends to separately installed pressure connections in accordance with 110.14(C)(2), it shall be permitted to have an allowable ampacity _____ the sum of the continuous load plus the noncontinuous load.
not less than
Unless marked otherwise, equipment terminals rated 100A or less (receptacles, switches, circuit breakers, fuses, and so on) and pressure connector terminals for 14 AWG through 1 AWG conductors must have the conductor sized according to the 60°C temperature rating as listed in Table 310.16, regardless of conductor insulation temperature rating.
true
When determining the number of current-carrying conductors, a grounding or bonding conductor shall not be counted when applying the provisions of 310.15(C)(1).
true
The branch-circuit overcurrent device and conductors for fixed storage-type water heater having a capacity of 120 gallons or less shall be sized not smaller than 125 percent of the rating of the _____.
water heater
What size THHN copper conductor can be used to interconnect 90°C rated power distribution blocks that are protected by a 200A overcurrent device serving a 150A continuous load?
2/0 AWG
What size overcurrent device will be required for a feeder supplying a 100A continuous and a 100A noncontinuous load?
225A
Conductors for general wiring not specifically permitted elsewhere in this Code to be covered or bare shall _____.
be insulated
What size THHN/THWN conductor is required for an air-conditioning unit if the nameplate requires a conductor ampacity of 34A? The terminals of all the equipment and circuit breakers are rated 75°C and the raceway is installed outdoors in a wet location.
10 AWG
The next higher standard rating overcurrent device above the ampacity of the ungrounded conductors being protected shall be permitted to be used, provided the _____.
conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads ampacity of the conductors does not correspond with the standard ampere rating of a fuse or circuit breaker next higher standard rating selected does not exceed 800A
There are four principal determinants of conductor operating temperature, one of which is _____ generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.
heat
A(An) _____ conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(C)(1).
neutral
The _____ rating of a conductor is the maximum temperature, at any location along its length, which the conductor can withstand over a prolonged period of time without serious degradation.
temperature
THHN can be described as _____.
thermoplastic insulation with a nylon outer cover having a maximum operating temperature of 90°C
Branch-circuit conductors for fixed electric space-heating equipment and any associated motors shall be sized not smaller than _____ percent of the load.
125 %
Feeder grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at _____ percent of the continuous and noncontinuous load.
100%
The branch-circuit overcurrent device and conductors for fixed storage-type water heater having a capacity of _____ gallons or less shall be sized not smaller than 125 percent of the rating of the water heater.
120 %
What size branch-circuit conductor is required for a 2,500W, 240V water heater?
14 AWG
The smallest size conductor(s) permitted for branch circuits, feeders, and services for residential, commercial, and industrial locations is _____.
14 AWG copper or 12 AWG aluminum
What's the ampacity of 1/0 XHHW-2 conductors if the ambient temperature is 108°F?
148A
If a branch circuit supplies a single nonmotor-operated appliance, the rating of overcurrent protection shall not exceed _____ percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.30A.
150 %
When four or more current-carrying conductors are bundled together for more than _____ in., the conductor allowable ampacity must be reduced according to the factors listed in Table 310.15(C)(1).
24 in.
Conductor adjustment factors shall not apply to conductors in raceways having a length not exceeding _____ in.
24 inches
What\'s the minimum size THHN conductor required for a 200A circuit breaker or fuse?
3/0 AWG
The ampacity adjustment factors in 310.15(C)(1) shall be applied to a metal wireway only where the number of current-carrying conductors in any cross section of the wireway exceeds _____.
30
What size conductors (paralleled in two raceways) are required for an 800A breaker that supplies a 600A continuous load?
300 kcmil
What's the ampacity of four current-carrying 8 THHN conductors installed in an ambient temperature of 90°F?
42A
What size conductor is required for a 400A breaker that supplies a 300A continuous load?
500 kcmil
What's the ampacity of 8 THHN/THWN conductors if the ambient temperature is 100°F?
50A
What size conductor is required for a 70A breaker that supplies a 65A noncontinuous load where the terminals are rated 75°C?
6 AWG
What size branch-circuit conductor (THHN) is required for a 32A continuous nonlinear load that requires three phase conductors and a neutral (four current-carrying conductors)?
8 AWG
What's the minimum size THHN conductor permitted to terminate on a 50A circuit breaker or fuse if the circuit breaker and equipment terminals are listed for 75°C conductor sizing?
8 AWG
Where installed in raceways, conductors _____ AWG and larger shall be stranded, unless specifically permitted or required elsewhere in the NEC.
8 AWG
If the circuits overcurrent device exceeds _____, the conductor ampacity shall have a rating not less than the rating of the overcurrent device.
800A
If the ampacity of a conductor doesn\'t correspond with the standard ampere rating of a fuse or circuit breaker, the next size up overcurrent protective device is permitted. This applies only if the conductors supply multioutlet receptacles for portable cord-and-plug-connected loads.
FALSE
The neutral conductor of a 3-wire wye circuit from a 4-wire, three-phase, wye system isn\'t considered a current-carrying conductor for the purpose of applying bundle adjustment factors.
FALSE
The neutral conductor that carries only the unbalanced current from a 3-wire 120/240v circuit or 4-wire, 120/208v three-phase wye circuit, is considered a current-carrying conductor for the purpose of applying the adjustment factors of Table 310.15(C)(1).
FALSE
In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, three-phase, _____ connected system, the common conductor is a current-carrying conductor and subject to the adjustment provisions of 310.15(C)(1).
wye-
Where a circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent protective device must not be less than the noncontinuous load plus _____ percent of the continuous load.
125%
The minimum size copper conductor permitted for voltage ratings up to 2,000V shall be _____ AWG.
14 AWG
What's the adjusted ampacity of 10 THHN conductors when nine current-carrying conductors are installed in a raceway or cable?
28A
What size overcurrent protection will be required for a branch circuit supplying a 32A continuous nonlinear load?
40A
What's the minimum size THHN conductor permitted to terminate on a 50A circuit breaker or fuse?
6 AWG
What's the minimum size THHN conductor permitted to terminate on a 70A circuit breaker or fuse?
6 AWG
If cables meeting the requirements in 310.15(C)(1)(d)(1) through (C)(1)(d)(3) with more than 20 current-carrying conductors are installed longer than 24 in. without maintaining spacing, are stacked, or are supported on bridle rings, a _____ percent adjustment factor shall be applied.
60 %
What's the ampacity of an 8 THHN conductor when installed in a walk-in cooler (dry location) if the ambient temperature is 50°F?
63A
For circuits rated 100A or less, when the equipment terminals are listed for use with 75°C conductors, the _____ column of Table 310.16 shall be used to determine the ampacity of THHN conductors.
75-degrees celsius
What's the ampacity of 1/0 XHHW-2 aluminum conductors if the ambient temperature is 154°F?
78A
Insulated conductors rated 600V with the letters "HH" in their designation have a _____ insulation rating.
90-degrees celsius
In accordance with Article 310, temperature correction and adjustment factors are permitted to be applied to the ampacity for the temperature rating of the _____, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C).
conductor
The temperature rating associated with the ampacity of a _____ shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device.
conductor
The temperature rating of a conductor is the maximum operating temperature the conductor insulation can withstand (without serious damage) over a prolonged period. The _____ provide guidance for adjusting conductor ampacities for different conditions.
conductor allowable ampacities ambient temperature correction factors over three current-carrying conductors adjustment factors
Feeder conductors shall be permitted to be sized at 100 percent of the continuous and noncontinuous load where a portion of the feeder is connected at both its supply and load ends to separately installed pressure connections.
true
In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, three-phase, wye-connected system, the common conductor is not a current-carrying conductor and not subject to the adjustment provisions of 310.15(C)(1).
true
What size conductor is required for a 90A breaker that supplies an 85A noncontinuous load?
3 AWG
What size aluminum conductor is required for a 150A breaker that supplies a 120A continuous load?
3/0 AWG
The neutral conductor of a balanced 4-wire, three-phase wye circuit that\'s more than 50 percent loaded with nonlinear loads (electric-discharge lighting, electronic ballasts, dimmers, controls, computers, laboratory test equipment, medical test equipment, recording studio equipment, and so forth) isn\'t considered a current-carrying conductor for the purpose of applying bundle adjustment factors.
FALSE
Conductors shall have their ampacity determined using the _____ column of Table 310.16 for circuits rated over 100A, or marked for conductors larger than 1 AWG, unless the equipment terminals are listed for use with higher temperature-rated conductors.
ampacities
Feeder tap conductors not over 25 ft in length are permitted, provided the _____.
are suitably protected from physical damage and terminate at a single circuit breaker or a single set of fuses that limits the load to the ampacity of the conductors
In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, three-phase, wye-connected system, the common conductor _____ a current-carrying conductor.
shall be counted as
SOW can be described as _____.
thermoset suitable for damp and wet locations having 600V insulation
What's the adjusted ampacity of 10 THHN conductors when four current-carrying conductors are installed in a raceway or cable?
32A
What size conductor is required for a 90A breaker that supplies an 85A noncontinuous load where the terminals are rated 75°C?
4 AWG
Conductor sizes are expressed in American Wire Gage (AWG) from 18 AWG through 4/0 AWG. Conductors larger than _____ are expressed in circular mils.
4/0 AWG
What size aluminum conductor is required for a 200A breaker that supplies a 180A noncontinuous load?
4/0 AWG
What size feeder conductor will be required for a feeder supplying a 100A continuous and a 100A noncontinuous load?
4/0 AWG
Branch-circuit conductors for fixed electric space-heating equipment and any associated motors shall be sized not smaller than 150 percent of the load.
false
The ampacities listed in Table 310.16 apply only when the ambient temperature is 40°C and there are no more than two current-carrying conductors bundled together. If the ambient temperature isn\'t 40°C, or there are more than two current-carrying conductors in a raceway, the allowable ampacities must be corrected and/or adjusted to reflect the ampacity under the conditions of use.
false
On a 4-wire, three-phase wye circuit where the major portion of the neutral load consists of _____ loads, the neutral conductor shall be considered a current-carrying conductor.
nonliner
Where a branch circuit supplies continuous loads, or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
true
What size aluminum feeder conductor will be required for a feeder supplying a 100A continuous and a 100A noncontinuous load?
300 kcmil
Terminals for equipment rated over 100A and pressure connector terminals for conductors larger than 1 AWG must have the conductor sized according to the 75°C temperature rating as listed in Table 310.16.
TRUE
Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor for the purpose of applying the adjustment factors of 310.15(C)(1)).
True
The ampacity of a conductor can be different along the length of the conductor. The higher calculated ampacity can be used if the lower ampacity portion of the circuit is no more than 10 ft, or no more than 10 percent of the length of the higher ampacity portion of the circuit conductors, whichever is less.
TRUE
The maximum overcurrent protective device size for 14 AWG is 15A, 12 AWG is 20A, and 10 AWG is 30A. This is a general rule, but it doesn\'t apply to motor or air conditioner loads according to 240.4(G).
TRUE
