For the service shown, the GEC to building steel must be at least ___ AWG in size.

For the service shown, the GEC to building steel must be at least ___ AWG in size.

• A. 3/0
• B. 2/0
• C. 2
• D. 1/0

Answer: (B)

The size of the grounding electrode conductor (GEC) to a building’s steel is determined by the rating of the service disconnect. The higher the service rating, the larger the GEC must be to safely carry fault current back to the source and allow the overcurrent device to trip properly. Per NEC 250.122, the minimum copper GEC size is set by the main OCPD rating. For a 600 A main service, the required minimum copper GEC is 2/0 AWG. Therefore, the GEC to the building steel must be at least 2/0 AWG. (Using aluminum would have a different minimum size.)

The size of the grounding electrode conductor (GEC) to a building’s steel is determined by the rating of the service disconnect. The higher the service rating, the larger the GEC must be to safely carry fault current back to the source and allow the overcurrent device to trip properly. Per NEC 250.122, the minimum copper GEC size is set by the main OCPD rating. For a 600 A main service, the required minimum copper GEC is 2/0 AWG. Therefore, the GEC to the building steel must be at least 2/0 AWG. (Using aluminum would have a different minimum size.)