Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A detached garage for a dwelling unit is supplied by a 60A feeder from the main house panel. The feeder consists of four insulated copper conductors (two ungrounded, one grounded, and one equipment grounding conductor) in a single conduit. The conductors are 6 AWG copper, rated for 75°C. What is the minimum size required for the equipment grounding conductor (EGC) for this feeder?
- A10 AWG copper
- B6 AWG copper
- C4 AWG copper
- D8 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: A. 10 AWG copper
According to NEC Table 250.122, for an overcurrent protective device rating of 60A, the minimum size required for the equipment grounding conductor (EGC) is 10 AWG copper. This table correlates the EGC size to the rating of the overcurrent device protecting the circuit.
Why the other options are wrong
- B. 6 AWG copper is the size of the ungrounded conductors, but the EGC can be smaller.
- C. 4 AWG copper is significantly larger than required, leading to unnecessary cost.
- D. 8 AWG copper is larger than required, leading to unnecessary cost.
Feeder Equipment Grounding Conductor Sizing
The size of an equipment grounding conductor (EGC) for feeders and branch circuits is determined by the rating of the overcurrent protective device (OCPD) ahead of the circuit, as specified in NEC Table 250.122.
- Sized based on the OCPD rating, not the conductor ampacity.
- Referenced in NEC Table 250.122.
- Ensures effective ground-fault current path.
- Must be copper, aluminum, or copper-clad aluminum.
Memory trick: EGC's Size: The breaker's rating dictates the ground's measure.