E2 NEC Compliance 3 — Questions and Answers
Question 1: NEC 310.15(B) permits ambient temperature correction factors to be applied to conductor ampacity. What reference temperature is used for conductors rated 60°C through 90°C in standard NEC tables?
- 25°C
- 30°C (Correct answer)
- 40°C
- 60°C
Correct answer: 30°C
The NEC ampacity tables are based on a 30°C (86°F) ambient temperature; correction factors must be applied for other ambient conditions.
Question 2: Under NEC 408.36, panelboards used as service equipment in commercial occupancies must be rated for use as service equipment, which requires what additional protection?
- GFCI on all circuits
- A main overcurrent protective device or multiple main breakers not exceeding 6 (Correct answer)
- A separate disconnect outside the panel
- Surge protection on the feeder
Correct answer: A main overcurrent protective device or multiple main breakers not exceeding 6
NEC 408.36 requires panelboards used as service equipment to have a main overcurrent device or not more than six circuit breakers to serve as the main disconnect.
Question 3: NEC 285.25 requires Type 1 SPDs installed on 120/240V single-phase services to be connected to which conductors?
- Each ungrounded conductor and the neutral (Correct answer)
- Each ungrounded conductor and the equipment grounding conductor
- The neutral and grounding electrode conductor only
- Line-to-line across the two ungrounded conductors only
Correct answer: Each ungrounded conductor and the neutral
Type 1 SPDs must connect between each ungrounded conductor and the neutral to provide proper surge protection across all legs.
Question 4: What does NEC 230.95 require on solidly grounded wye services of more than 150 volts to ground but not exceeding 600 volts phase-to-phase?
- AFCI protection
- Ground-fault protection of equipment (GFPE) (Correct answer)
- Differential relaying
- Double-ended switching
Correct answer: Ground-fault protection of equipment (GFPE)
NEC 230.95 mandates ground-fault protection of equipment for solidly grounded wye services over 150V to ground to prevent equipment damage from arcing ground faults.
Question 5: Per NEC 314.28(A)(1), straight pulls in pull boxes require the box length to be at least how many times the trade size of the largest raceway?
- 4 times
- 6 times
- 8 times (Correct answer)
- 12 times
Correct answer: 8 times
For straight pulls, NEC 314.28(A)(1) requires the box length to be at least eight times the trade size of the largest raceway entering the box.
Question 6: NEC 501.15 governs conduit seals in Class I hazardous locations. Where must seals be installed relative to the boundary of the hazardous area?
- Within 36 inches of the enclosure
- Within 18 inches of the enclosure or the boundary, whichever is less
- Within 18 inches of the hazardous area boundary (Correct answer)
- At every junction box within the hazardous area
Correct answer: Within 18 inches of the hazardous area boundary
Conduit seals must be placed within 18 inches of the hazardous area boundary to prevent ignitable vapors from traveling through the conduit system.
Question 7: According to NEC 250.66, the minimum size of the grounding electrode conductor for a service using 350 kcmil copper service conductors is:
- 4 AWG copper
- 2 AWG copper (Correct answer)
- 1/0 AWG copper
- 3/0 AWG copper
Correct answer: 2 AWG copper
NEC Table 250.66 shows that 350 kcmil service conductors require a minimum 2 AWG copper grounding electrode conductor.
E2 NEC Compliance 3
NEC 310.15(B) permits ambient temperature correction factors to be applied to conductor ampacity.
What reference temperature is used for conductors rated 60°C through 90°C in standard NEC tables?