In a poured concrete grade beam, what is the maximum size GEC required from the service equipment to the rebar in the bottom of the grade beam?

• A. 2/0
• B. 4
• C. 6
• D. 1/0

Answer: (B)

When a concrete-encased electrode is used as part of the grounding system, such as reinforcing steel in a poured grade beam, the grounding electrode conductor must be sized to provide a solid fault path. The NEC specifies a minimum size for the GEC to a concrete-encased electrode: copper conductors must be at least 4 AWG (or 2 AWG if aluminum). This minimum guarantees adequate current-carrying capacity and a reliable connection to earth for fault conditions. Therefore, the size that meets this requirement from the service equipment to the rebar at the bottom of the grade beam is 4 AWG copper. The other options are either undersized (6 AWG) or larger than the minimum (2/0, 1/0), which are allowed but not the required minimum.