Journeyman Electrician's Conductor Sizing and Ampacity Flashcards

Nine current-carrying conductors are installed in a single conduit. What derating factor applies per NEC 310.15(C)(1)?

Answer: 70%

For 7–9 current-carrying conductors in a raceway, a 70% adjustment factor applies per NEC 310.15(C)(1).

What is the minimum conductor size for a 20A branch circuit supplying continuous loads using 60°C-rated terminations?

Answer: 12 AWG

12 AWG copper at 60°C is rated 20A, which satisfies the 20A continuous circuit requirement per NEC 310.14.

An ambient temperature of 50°C is encountered in a boiler room. If the base table temperature is 30°C, which correction factor must be applied to conductor ampacity?

Answer: Multiply by 0.71

For 75°C-rated conductors in a 50°C ambient, NEC Table 310.15(B)(2)(a) requires a 0.71 correction factor.

Which of the following conductors is NOT counted as a current-carrying conductor for bundling derating purposes?

Answer: Neutral carrying unbalanced current only

A neutral that carries only unbalanced current in a 3-wire circuit is not counted as a current-carrying conductor per NEC 310.15(E).

What is the ampacity of 1/0 AWG copper THHN at 90°C per NEC Table 310.15(B)(16)?

Answer: 170A

1/0 AWG copper at 90°C has an ampacity of 170A per NEC Table 310.15(B)(16).

A 4/0 AWG aluminum conductor is used in underground conduit. Which insulation type is required for a wet location?

Answer: XHHW or THWN

XHHW or THWN insulation is rated for wet locations; THHN is dry-location only and cannot be used in underground conduit.

A motor branch circuit requires conductors sized at least 125% of the motor full-load current (FLC). If FLC = 28A, what is the minimum conductor ampacity?

Answer: 35A

125% of 28A = 35A, so conductors must have at least 35A ampacity per NEC 430.22.