Master Electrician Exam (NEC)Grounding and BondingMedium
A master electrician is installing a new 200A, 120/240V, single-phase service for a residential dwelling. The service uses two 3/0 AWG copper ungrounded conductors and a 1/0 AWG copper grounded conductor. The grounding electrode system consists of a metal underground water pipe electrode and a supplemental ground rod. What is the minimum size copper grounding electrode conductor (GEC) required to connect to the metal underground water pipe electrode?
- A1/0 AWG
- B2 AWG
- C4 AWG
- D6 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. 4 AWG
According to NEC 250.66(A), the GEC to a metal underground water pipe electrode must not be smaller than the sizes specified in Table 250.66. For 3/0 AWG copper service conductors, the minimum size copper GEC to a water pipe electrode is 4 AWG.
Why the other options are wrong
- A. Incorrect. This size is only required for larger service conductors or specific types of electrodes.
- B. Incorrect. This size is larger than required for 3/0 AWG copper service conductors to a water pipe.
- D. Incorrect. This size is for smaller service conductors or specific types of electrodes.
GEC Sizing for Water Pipe Electrode
The grounding electrode conductor connecting to a metal underground water pipe electrode is sized based on the largest ungrounded service-entrance conductors, with specific rules and minimums.
- Sized per NEC 250.66 and Table 250.66.
- Must be connected to the water pipe within 5 feet of its entrance into the building.
- The water pipe must be in direct contact with earth for at least 10 feet.
Memory trick: Water Pipe GEC: Check the Service, Find the Table, Get the Size.