Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A journeyman is installing a new 200-ampere service in a residence. The service-entrance conductors are 3/0 AWG copper. If the grounding electrode conductor (GEC) is connected to a metal underground water pipe and supplemented by a driven ground rod, what is the minimum size copper GEC required for the connection to the water pipe, according to NEC® Table 250.66?
- ANo. 8 AWG
- BNo. 4 AWG
- CNo. 2 AWG
- DNo. 6 AWG
Show answer & explanationAnswer & explanation
Correct answer: B. No. 4 AWG
According to NEC® Table 250.66, for service-entrance conductors of 3/0 AWG copper, the minimum size copper grounding electrode conductor required is No. 4 AWG. This size applies to the connection to the water pipe, which is the primary electrode for sizing per this table.
Why the other options are wrong
- A. No. 8 AWG is too small for 3/0 AWG service conductors.
- C. No. 2 AWG is larger than the minimum required for 3/0 AWG service conductors.
- D. No. 6 AWG is the minimum for a driven ground rod, but not for the main GEC to the water pipe with 3/0 AWG service conductors.
GEC Sizing to Water Pipe
The size of the grounding electrode conductor connecting to a metal underground water pipe (when used as a grounding electrode) is determined by the size of the largest ungrounded service-entrance conductors, using NEC® Table 250.66.
- Primary reference: NEC® Table 250.66.
- Based on the size of the largest ungrounded service-entrance conductor.
- The water pipe must also be supplemented by another electrode.
Memory trick: Water pipe's GEC size flows from the service wire's girth.