Journeyman Electrician Exam (NEC)Grounding and BondingMedium
A journeyman is installing a new 200-ampere, 120/240-volt single-phase service. The service-entrance conductors are 3/0 AWG copper. The grounding electrode conductor is connected to a metal underground water pipe electrode and a supplemental ground rod. What is the minimum size of the grounding electrode conductor where it connects to the metal underground water pipe?
- A2 AWG copper
- B6 AWG copper
- C8 AWG copper
- D4 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: D. 4 AWG copper
According to NEC Table 250.66, for 3/0 AWG copper service-entrance conductors, the minimum size grounding electrode conductor is 4 AWG copper. This size applies to the connection to the metal underground water pipe. The supplemental rod connection can be smaller, but the water pipe requires sizing based on the service conductors.
Why the other options are wrong
- A. This size is larger than required by code for 3/0 AWG copper service conductors.
- B. This size is applicable for a supplemental ground rod, but not for the connection to the main water pipe electrode with 3/0 AWG service conductors.
- C. This size is too small for service-entrance conductors of 3/0 AWG copper.
GEC Sizing to Water Pipe
The grounding electrode conductor connected to a metal underground water pipe electrode must be sized according to NEC Table 250.66, based on the size of the service-entrance conductors.
- Applies to metal underground water pipe electrode.
- Sized from NEC Table 250.66.
- Based on the largest ungrounded service-entrance conductor size.
Memory trick: Water pipe GEC: Service conductor's call!