Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A commercial building has a 200A, 480Y/277V, 3-phase, 4-wire service. The service entrance conductors are 250 kcmil copper. What is the minimum size required for the service grounded conductor (neutral) if it is copper?
- A4 AWG
- B1/0 AWG
- C3/0 AWG
- D2 AWG
Show answer & explanationAnswer & explanation
Correct answer: B. 1/0 AWG
According to NEC 250.24(C)(1), the service grounded conductor shall not be smaller than the minimum size specified in Table 250.102(C)(1). For 250 kcmil copper service entrance conductors, the table requires a 1/0 AWG copper grounded conductor.
Why the other options are wrong
- A. 4 AWG copper is too small for 250 kcmil service entrance conductors.
- C. 3/0 AWG copper is larger than the minimum required size for 250 kcmil service entrance conductors.
- D. 2 AWG copper is too small for 250 kcmil service entrance conductors.
Service Grounded Conductor Sizing (NEC 250.24(C)(1))
The service grounded conductor (neutral) must be sized to carry the maximum unbalanced current and provide a low-impedance path for ground-fault current, not smaller than the sizes specified in NEC 250.24(C)(1) and Table 250.102(C)(1).
- Sized based on the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.
- Must not be smaller than the sizes in NEC Table 250.102(C)(1).
- Must be capable of carrying the maximum unbalanced load (NEC 220.61).
Memory trick: Neutral is the balancing act, keeping current safe and sound.