Question

A 500 KCMIL copper 480/277 volt service is grounded to a metallic pipe in direct contact with the earth for above 10 ft structural steel and a concrete encased electrode. Exposed interior structural steel was found that was not intentionally grounded and could become energized. To bond this interior structural steel to the grounding electrode system, what's the smallest size copper wire allowed?

Answer 1

The smallest size copper wire allowed for bonding the interior structural steel to the grounding electrode system in this scenario would be a 4 AWG copper wire, as per the NEC Table 250.66 standards for grounding to a concrete-encased electrode.

Step-by-step explanation:

The question is related to the grounding and bonding requirements for electrical systems, specifically involving the correct sizing of a copper wire used to bond interior structural steel that was not intentionally grounded to the grounding electrode system. According to the National Electrical Code (NEC), which sets the standards for safe electrical installations, the size of the bonding conductor would be determined by referring to Table 250.66. Since the service size is 500 KCMIL, the NEC requires a grounding electrode conductor no smaller than 3/0 AWG copper when grounding to reinforcing steel or rod, pipe, or plate electrodes. However, if the grounding electrode conductor is connected to a concrete-encased electrode, as is the case here, the NEC allows a grounding electrode conductor of 4 AWG copper. Thus, a 4 AWG copper wire is the smallest size allowed for bonding the interior structural steel to the grounding electrode system in the scenario provided.