Journeyman Electrician's Conductor Sizing and Ampacity Flashcards
7 cards from real Journeyman Electrician’s Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Journeyman Electrician's Conductor Sizing and Ampacity flashcards as text
When conductors are installed in a conduit exposed to direct sunlight on a rooftop, what additional temperature adder is applied per NEC 310.15(B)(3)(c) for conduit within 7/8 inch of the roof?
Answer: 33°C
NEC 310.15(B)(3)(c) requires a 33°C temperature adder when conduit is within 7/8 inch above a rooftop.
A 3-phase, 4-wire circuit with a neutral conductor supplying non-linear loads (rich in harmonics) — how is the neutral counted for bundling derating?
Answer: Counted as one current-carrying conductor
When the neutral carries significant harmonic currents (non-linear loads), it must be counted as a current-carrying conductor per NEC 310.15(E).
What is the minimum size copper grounded (neutral) conductor for a 200A service per NEC Table 250.102(C)(1)?
Answer: 2 AWG
For a 200A service, NEC Table 250.102(C)(1) requires a minimum 2 AWG copper grounded conductor.
An installer uses 10 AWG copper THWN in a 75°C-rated panel. The 75°C ampacity of 10 AWG copper is 35A. A 40A breaker is installed. Is this code-compliant?
Answer: No, the conductor ampacity must equal or exceed the breaker rating
The conductor ampacity (35A) must equal or exceed the overcurrent protection rating (40A), so a 40A breaker on 10 AWG is not permitted.
Per NEC 240.4(D), what is the maximum overcurrent protection for 14 AWG copper conductors?
Answer: 15A
NEC 240.4(D) limits overcurrent protection for 14 AWG copper to a maximum of 15A.
What is the ampacity of 250 kcmil copper THHN at 90°C per NEC Table 310.15(B)(16)?
Answer: 290A
250 kcmil copper at 90°C has an ampacity of 290A per NEC Table 310.15(B)(16).
Two circuits share a conduit: Circuit A has 2 conductors, Circuit B has 4 conductors. How many current-carrying conductors are in the conduit for derating purposes?
Answer: 6
Both circuits' current-carrying conductors are counted together: 2 + 4 = 6 current-carrying conductors total.