Conductor Sizing and Protection Calculations.
What's the minimum size THHN conductor required for a 150A circuit breaker or fuse?
1/0 AWG
Overcurrent protection shall not exceed _____.
15A for 14 AWG copper. 20A for 12 AWG copper. 30A for 10 AWG copper.
Which of the following is(are) a standard size for circuit breakers and fuses?
25A. 90A. 350A.
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
What size conductor is required for a 70A breaker that supplies a 65A noncontinuous load?
4 AWG.
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 conductors (paralleled in three raceways) are required for a 1,200A breaker that supplies a 900A continuous load?
600 kcmil.
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°C
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.
One of the purposes of conductor overcurrent protection is to protect the conductors against excessive or dangerous heat.
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.
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.
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.
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
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's the ampacity of 1/0 XHHW-2 aluminum conductors if the ambient temperature is 154°F?
78A.
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.
