Master Electrician Exam (NEC)Grounding and BondingMedium
A master electrician is installing a new 480Y/277V, 3-phase, 4-wire service in a commercial building. The building has a structural steel frame that meets the requirements for a grounding electrode. What is the minimum length of structural steel that must be in direct contact with the earth to be considered a grounding electrode?
- A5 feet
- B20 feet
- C10 feet
- D30 feet
Show answer & explanationAnswer & explanation
Correct answer: C. 10 feet
According to NEC 250.52(A)(2), a metal underground water pipe or structural metal frame of the building that is in direct contact with the earth for 10 feet (3.0 m) or more can serve as a grounding electrode.
Why the other options are wrong
- A. This length is insufficient for structural steel to be considered a grounding electrode.
- B. While acceptable, this is not the minimum required length.
- D. While acceptable, this is not the minimum required length.
Structural Steel Grounding Electrode
The structural metal frame of a building, if in direct contact with the earth for 10 feet or more, can serve as a grounding electrode.
- Part of a grounding electrode system.
- Must be in direct contact with earth.
- Minimum 10 feet (3.0 m) contact length.
Memory trick: Electrodes grounded deep, secrets they keep.