Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A technician is installing a new service disconnect for a 400-ampere commercial service. The service conductors are 500 kcmil copper. What is the minimum size copper equipment grounding conductor required for this service, according to NEC® Table 250.122?
- ANo. 1 AWG
- BNo. 3 AWG
- C1/0 AWG
- DNo. 2 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. No. 2 AWG
According to NEC® Table 250.122, for an overcurrent device rating of 400 amperes, the minimum size copper equipment grounding conductor required is No. 2 AWG.
Why the other options are wrong
- A. No. 1 AWG is for overcurrent devices up to 500A, which is larger than the minimum required for 400A.
- B. No. 3 AWG is for overcurrent devices up to 200A, not 400A.
- C. 1/0 AWG is for overcurrent devices up to 600A, which is larger than the minimum required for 400A.
Equipment Grounding Conductor Sizing
The size of the equipment grounding conductor (EGC) is determined by the rating of the overcurrent protective device (OCPD) in the circuit, not the service conductor size, using NEC® Table 250.122.
- Based on overcurrent device rating.
- Table 250.122 is the primary reference.
- Applies to equipment grounding conductors, not grounding electrode conductors.
Memory trick: EGC size is tied to the Breaker's Guard, not the wire's length.