Journeyman Electrician Exam (NEC)Equipment and DevicesHard
A journeyman electrician is installing a 300-ampere, 208Y/120-volt service for a commercial building. The service conductors are 3/0 AWG copper with THHN insulation. What is the minimum size grounding electrode conductor (GEC) required if the service entrance conductors are not paralleled?
- ANo. 1/0 AWG copper
- BNo. 2 AWG copper
- CNo. 2/0 AWG copper
- DNo. 4 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. No. 2 AWG copper
According to NEC Table 250.66, the size of the grounding electrode conductor is based on the size of the largest ungrounded service-entrance conductor. For 3/0 AWG copper service conductors, the minimum size copper grounding electrode conductor is No. 2 AWG.
Why the other options are wrong
- A. No. 1/0 AWG copper is for 4/0 AWG or 250 kcmil service conductors.
- C. No. 2/0 AWG copper is for 350 kcmil or 400 kcmil service conductors.
- D. No. 4 AWG copper is for 1/0 AWG or 2/0 AWG service conductors, or smaller.
Grounding Electrode Conductor Sizing
Determining the minimum size of the grounding electrode conductor (GEC) based on the size of the largest ungrounded service-entrance conductor or equivalent area for paralleled conductors, as specified in NEC Table 250.66.
- Connects the grounding electrode to the service equipment enclosure.
- Size is dependent on the service conductor size, not the service overcurrent protection.
- NEC Table 250.66 is the primary reference.
Memory trick: Service wire size is key, GEC follows its decree!