Journeyman Electrician's Conductor Sizing and Ampacity Flashcards
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What is the maximum voltage drop recommended by NEC 210.19(A) informational note for branch circuit conductors?
Answer: 3%
NEC 210.19(A) informational note recommends a maximum voltage drop of 3% for branch circuits.
A 12 AWG copper conductor is rated 20A at 60°C and 25A at 90°C. If the equipment termination is rated 60°C, what ampacity must be used?
Answer: 20A, limited by the termination rating
The ampacity is limited to 20A because the termination is rated only 60°C, regardless of the conductor's higher insulation rating.
Per NEC 310.15(B)(3)(a), what adjustment factor applies to conductors installed in conduit exposed to direct sunlight on a rooftop where the conduit is 7 inches above the roof surface?
Answer: Add 14°C
When conduit is between 3.5 and 12 inches above a rooftop, NEC adds 14°C to the ambient temperature for ampacity calculations.
Two 500 kcmil conductors per phase are installed in parallel. Each 500 kcmil copper conductor at 75°C has 380A ampacity. What is the total ampacity for the parallel set?
Answer: 760A
Parallel conductors add their individual ampacities: 380A × 2 = 760A total per phase.
What is the minimum conductor size that may be used in parallel per NEC 310.10(H)(1)?
Answer: 1/0 AWG
NEC 310.10(H)(1) requires each parallel conductor to be at least 1/0 AWG copper or 1/0 AWG aluminum.
A conductor's ampacity is 100A, but the next standard overcurrent device size above 100A is 110A. Per NEC 240.4(B), can a 110A breaker be used?
Answer: Yes, the next standard size up is always permitted
NEC 240.4(B) permits using the next standard overcurrent device size when the conductor ampacity doesn't match a standard size.
When more than 20 current-carrying conductors are bundled together in a cable tray, what derating factor applies per NEC 310.15(C)(1)?
Answer: 50%
For more than 20 current-carrying conductors in a raceway or cable tray, a 50% adjustment factor applies per NEC 310.15(C)(1).