Journeyman Electrician’s Exam Journeyman Electrician's Conductor Sizing and Ampacity 2 — Questions and Answers
Question 1: A 120/240V single-phase service uses 2 AWG copper conductors. What is the standard ampacity of 2 AWG copper at 75°C per NEC Table 310.15(B)(16)?
- 95A
- 115A (Correct answer)
- 130A
- 105A
Correct answer: 115A
2 AWG copper conductors have a standard ampacity of 115A at 75°C per NEC Table 310.15(B)(16).
Question 2: Three current-carrying conductors are bundled in a conduit. According to NEC 310.15(C)(1), what adjustment factor applies?
- No adjustment needed (Correct answer)
- 80% of table ampacity
- 70% of table ampacity
- 50% of table ampacity
Correct answer: No adjustment needed
NEC 310.15(C)(1) requires no adjustment factor for 3 or fewer current-carrying conductors.
Question 3: Which conductor material has higher conductivity, requiring a smaller gauge for equivalent ampacity?
- Aluminum
- Copper-clad aluminum
- Copper (Correct answer)
- Nickel-plated copper
Correct answer: Copper
Copper has higher conductivity than aluminum, so it carries more current at the same wire gauge.
Question 4: A feeder supplies a continuous load of 80A. What is the minimum conductor ampacity required before applying breaker sizing?
- 80A
- 90A
- 100A (Correct answer)
- 125A
Correct answer: 100A
Conductors for continuous loads must be sized at 125% of the load (80A × 1.25 = 100A) per NEC 215.2.
Question 5: What NEC table is used to find the ampacity of conductors 0-2000V with not more than 3 current-carrying conductors in a raceway?
- Table 310.15(B)(2)
- Table 310.15(B)(16) (Correct answer)
- Table 310.12
- Table 240.4(D)
Correct answer: Table 310.15(B)(16)
NEC Table 310.15(B)(16) provides ampacity values for conductors up to 2000V with no more than 3 current-carrying conductors.
Question 6: A 6 AWG aluminum conductor has what standard ampacity at 75°C per NEC Table 310.15(B)(16)?
- 55A
- 65A (Correct answer)
- 75A
- 50A
Correct answer: 65A
6 AWG aluminum at 75°C has an ampacity of 65A per NEC Table 310.15(B)(16).
Question 7: When using THWN-2 insulation at 75°C in a wet location, which temperature column applies for ampacity from NEC Table 310.15(B)(16)?
- 60°C column
- 75°C column (Correct answer)
- 90°C column
- Either 75°C or 90°C column
Correct answer: 75°C column
When equipment terminations are rated 75°C, the 75°C column must be used even if the insulation is rated higher.
Journeyman Electrician’s Exam Journeyman Electrician's Conductor Sizing and Ampacity 2
A 120/240V single-phase service uses 2 AWG copper conductors.
What is the standard ampacity of 2 AWG copper at 75°C per NEC Table 310.15(B)(16)?