Journeyman Electrician Exam (NEC)Grounding and BondingHard
A journeyman is inspecting the grounding system of a new commercial service. The building has a metal frame, and the service-entrance conductors are 750 kcmil copper. The grounding electrode conductor is connected to the building's metal frame. What is the minimum size of the GEC to the metal frame?
- A4/0 AWG copper
- B250 kcmil copper
- C2/0 AWG copper
- D3/0 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. 250 kcmil copper
According to NEC Table 250.66, for service-entrance conductors of 750 kcmil copper, the minimum size grounding electrode conductor is 250 kcmil copper. The building steel is considered a grounding electrode and its GEC is sized based on the service conductors.
Why the other options are wrong
- A. This size is too small for 750 kcmil service conductors.
- C. This size is too small for 750 kcmil service conductors.
- D. This size is too small for 750 kcmil service conductors.
GEC Sizing to Building Steel
When a building's metal frame is used as a grounding electrode, the grounding electrode conductor (GEC) is sized according to NEC Table 250.66, based on the size of the service-entrance conductors.
- Building steel is a common type of grounding electrode.
- GEC size determined by NEC Table 250.66.
- Based on the largest ungrounded service-entrance conductor size.
Memory trick: Steel Frame GEC: Service size dictates the gain!