Journeyman Electricianâs Exam Journeyman Electrician's Conductor Sizing and Ampacity 4 â Questions and Answers
Question 1: 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?
- 5°C
- 15°C
- 30°C
- 33°C (Correct answer)
Correct 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.
Question 2: A 3-phase, 4-wire circuit with a neutral conductor supplying non-linear loads (rich in harmonics) â how is the neutral counted for bundling derating?
- Not counted
- Counted as one current-carrying conductor (Correct answer)
- Counted as two current-carrying conductors
- Ignored if load is balanced
Correct 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).
Question 3: What is the minimum size copper grounded (neutral) conductor for a 200A service per NEC Table 250.102(C)(1)?
- 2 AWG (Correct answer)
- 4 AWG
- 6 AWG
- 1/0 AWG
Correct answer: 2 AWG
For a 200A service, NEC Table 250.102(C)(1) requires a minimum 2 AWG copper grounded conductor.
Question 4: 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?
- Yes, if the load is non-continuous
- No, the conductor ampacity must equal or exceed the breaker rating (Correct answer)
- Yes, the next standard breaker size up is allowed
- No, 10 AWG is limited to 30A always
Correct 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.
Question 5: Per NEC 240.4(D), what is the maximum overcurrent protection for 14 AWG copper conductors?
- 20A
- 15A (Correct answer)
- 25A
- 30A
Correct answer: 15A
NEC 240.4(D) limits overcurrent protection for 14 AWG copper to a maximum of 15A.
Question 6: What is the ampacity of 250 kcmil copper THHN at 90°C per NEC Table 310.15(B)(16)?
- 255A
- 290A (Correct answer)
- 300A
- 315A
Correct answer: 290A
250 kcmil copper at 90°C has an ampacity of 290A per NEC Table 310.15(B)(16).
Question 7: 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?
- 4
- 6 (Correct answer)
- 2
- Depends on load balance
Correct answer: 6
Both circuits' current-carrying conductors are counted together: 2 + 4 = 6 current-carrying conductors total.
Journeyman Electricianâs Exam Journeyman Electrician's Conductor Sizing and Ampacity 4
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?