Journeyman Electrician Exam (NEC)Grounding and BondingEasy
An electrician is designing the grounding system for a new service where a metal underground water pipe is available as a grounding electrode. What is the minimum length of contact with the earth required for this water pipe to qualify as a grounding electrode, according to NEC® 250.52(A)(1)?
- A15 ft (4.5 m)
- B10 ft (3.0 m)
- C5 ft (1.5 m)
- D20 ft (6.0 m)
Show answer & explanationAnswer & explanation
Correct answer: B. 10 ft (3.0 m)
NEC® 250.52(A)(1) specifies that a metal underground water pipe must be in direct contact with the earth for 10 ft (3.0 m) or more to qualify as a grounding electrode.
Why the other options are wrong
- A. 15 ft is more than the minimum required but not the minimum itself.
- C. 5 ft is insufficient for a metal underground water pipe to qualify as a grounding electrode.
- D. 20 ft is more than the minimum required but not the minimum itself; it is the minimum length for a ground ring or concrete-encased electrode.
Metal Water Pipe Electrode Length
For a metal underground water pipe to be considered an effective grounding electrode, it must have at least 10 ft (3.0 m) of direct contact with the earth, as specified in NEC® 250.52(A)(1).
- Applies specifically to metal underground water pipes.
- Minimum 10 ft (3.0 m) of direct earth contact.
- Must be supplemented by an additional electrode (NEC® 250.53(D)(2)).
Memory trick: Water pipe needs a 'ten-foot dive' to be a good ground.