Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsEasy
A new commercial building requires a 200A, 120/240V, single-phase service. The service entrance conductors will be run in RMC and have an ampacity of 200A. What is the minimum size copper grounding electrode conductor (GEC) required if the largest service-entrance ungrounded conductor is 3/0 AWG copper?
- A2 AWG copper
- B4 AWG copper
- C8 AWG copper
- D6 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. 4 AWG copper
According to NEC Table 250.66, for a service-entrance conductor of 3/0 AWG copper, the minimum size copper grounding electrode conductor (GEC) required is 4 AWG copper. This table correlates the GEC size to the largest ungrounded service-entrance conductor.
Why the other options are wrong
- A. 2 AWG copper is larger than required for 3/0 AWG service conductors, leading to unnecessary cost.
- C. 8 AWG copper is too small for 3/0 AWG service conductors per NEC Table 250.66.
- D. 6 AWG copper is too small for 3/0 AWG service conductors per NEC Table 250.66.
Grounding Electrode Conductor Sizing
The sizing of the grounding electrode conductor (GEC) is determined by the size of the largest ungrounded service-entrance conductor, as specified in NEC Table 250.66.
- NEC Table 250.66 is the primary reference.
- Size depends on the largest ungrounded service conductor (copper or aluminum).
- GEC must be copper if service conductors are copper, or aluminum if service conductors are aluminum.
Memory trick: Grounding's Core Connection: Service size dictates the Earth's protection.