Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A master electrician is installing new service entrance conductors for a dwelling unit. The service is 200A, 120/240V, single-phase. The service entrance conductors are 2/0 AWG copper with THWN insulation. What is the minimum size aluminum grounded conductor (neutral) required for this service?
- A4/0 AWG aluminum
- B3/0 AWG aluminum
- C2/0 AWG aluminum
- D1/0 AWG aluminum
Show answer & explanationAnswer & explanation
Correct answer: C. 2/0 AWG aluminum
According to NEC 250.24(D)(1), the grounded conductor shall not be smaller than specified in Table 250.102(C)(1). For 200A service conductors (2/0 AWG copper), Table 250.102(C)(1) requires a minimum of 2/0 AWG aluminum grounded conductor.
Why the other options are wrong
- A. 4/0 AWG aluminum is much larger than required for this application.
- B. 3/0 AWG aluminum is larger than required for this application.
- D. 1/0 AWG aluminum is typically for 150A services, not 200A.
Service Grounded Conductor Sizing (250.24)
The sizing of the neutral conductor in a service, which must be large enough to carry the maximum unbalanced current and not smaller than specified in NEC Table 250.102(C)(1).
- Carries unbalanced current.
- Minimum size based on service entrance conductor size.
- Refer to NEC Table 250.102(C)(1).
Memory trick: Neutral needs 'Table Talk' (250.102) and 'Balance Check' (unbalanced current).