Where the DC side GES is six AWG copper and the AC system GES is one AWG copper, what is the minimum size for the bonding conductor connecting the two systems together?

• A. 4 AWG copper
• B. 1 AWG copper
• C. 6 AWG copper
• D. 8 AWG copper

Answer: (B)

Bonding the two grounding electrode systems must provide a single, low-impedance path for fault currents between them. The bonding conductor must be not smaller than the largest equipment grounding conductor in either system. Here, the DC side uses 6 AWG copper and the AC system uses 1 AWG copper, so the largest EGC is 1 AWG. Therefore the bonding conductor must be at least 1 AWG copper. Conductors smaller than that would be undersized. The minimum size is 1 AWG copper.