Master Electrician Exam (NEC)Grounding and BondingMedium
A master electrician is inspecting a previously installed grounding electrode system for a dwelling. The system includes a metal underground water pipe electrode and a supplemental electrode. The water pipe has 10 feet of contact with the earth. What is the minimum length of the supplemental electrode required if it is a ground rod, according to NEC 250.53(A)(2)?
- A8 feet
- B10 feet
- C6 feet
- D4 feet
Show answer & explanationAnswer & explanation
Correct answer: A. 8 feet
NEC 250.53(A)(2) states that if a metal underground water pipe electrode is used, it must be supplemented by an additional electrode, and the supplemental electrode must comply with 250.52(A)(2) through (A)(8). For a ground rod [250.52(A)(5)], the minimum length driven into the earth is 8 feet.
Why the other options are wrong
- B. This is the minimum contact length for a water pipe, not a ground rod.
- C. This is too short for a ground rod electrode.
- D. This is too short for a ground rod electrode.
Ground Rod Electrode Length
A rod electrode used as part of a grounding electrode system must be a minimum of 8 feet in length and driven fully into the earth.
- Part of the NEC 250.52(A)(5) requirements.
- Must be driven to a minimum 8-foot depth.
- Often used as a supplemental electrode.
Memory trick: Eight feet for the rod, if water pipe's not enough.