E2 Services, Feeders, Branch Circuits 3 — Questions and Answers
Question 1: Per NEC 230.70, where must the service disconnecting means be located in a commercial building?
- At the meter base only
- At the nearest accessible point to the service entrance conductors' entry into the building (Correct answer)
- In the main electrical room regardless of entry point
- Within 25 feet of the utility transformer
Correct answer: At the nearest accessible point to the service entrance conductors' entry into the building
NEC 230.70(A)(1) requires the service disconnect to be at the nearest accessible point to the service entrance conductors' entry into the building.
Question 2: What is the maximum number of disconnects allowed as the service disconnecting means for a single building per NEC 230.71?
- Two
- Four
- Six (Correct answer)
- Eight
Correct answer: Six
NEC 230.71(A) limits the service disconnecting means to a maximum of six switches or circuit breakers.
Question 3: A branch circuit protected by a 20-ampere overcurrent device supplies receptacles in a commercial office. What is the minimum conductor size permitted for this branch circuit?
- 14 AWG copper
- 12 AWG copper (Correct answer)
- 10 AWG copper
- 8 AWG copper
Correct answer: 12 AWG copper
NEC 210.19(A) and Table 310.15(B)(16) require 12 AWG minimum for a 20-ampere branch circuit.
Question 4: Per NEC 215.10, feeder ground-fault protection of equipment is required for solidly grounded wye services exceeding what voltage and ampere rating?
- 120/208V services over 400 amperes
- 277/480V services over 1000 amperes
- Solidly grounded wye services of more than 150V to ground not exceeding 600V and 1000 amperes or more (Correct answer)
- Any 480V service over 800 amperes
Correct answer: Solidly grounded wye services of more than 150V to ground not exceeding 600V and 1000 amperes or more
NEC 215.10 requires feeder GFPE on solidly grounded wye services with more than 150V to ground, not exceeding 600V, rated 1000A or more.
Question 5: A commercial building has a 480Y/277V service. What is the maximum voltage to ground for general lighting branch circuits supplying fluorescent fixtures in this building?
- 120 volts
- 208 volts
- 277 volts (Correct answer)
- 480 volts
Correct answer: 277 volts
NEC 210.6(D) permits branch circuits up to 277V to ground for listed electric-discharge luminaires in commercial occupancies.
Question 6: Per NEC 230.24(B), service conductors run above a roof surface must maintain a minimum clearance above the roof of:
- 3 feet
- 8 feet
- 18 inches for the general case (Correct answer)
- 36 inches
Correct answer: 18 inches for the general case
NEC 230.24(B) generally requires 8 feet of clearance, but the standard minimum above a roof surface where the conductors pass through is 18 inches for the general case with a 300V or less limitation.
Question 7: Which conductor is NOT required to be counted when calculating the total number of conductors in a conduit for a 3-phase, 4-wire feeder per NEC Chapter 9?
- The equipment grounding conductor if it is the same size as the phase conductors
- The grounded (neutral) conductor
- A parallel neutral conductor
- A separately installed equipment grounding conductor (Correct answer)
Correct answer: A separately installed equipment grounding conductor
Equipment grounding conductors are included in conduit fill calculations per NEC Chapter 9 Table 1 notes; all current-carrying and grounding conductors count.
E2 Services, Feeders, Branch Circuits 3
Per NEC 230.70, where must the service disconnecting means be located in a commercial building?