The minimum sizes for grounds used for distribution and transmission, respectively, are:

• A. 4/0 and 2/0
• B. 2/0 and #2
• C. #2 and 2/0
• D. 2/0 and 4/0

Answer: (C)

The key idea is that grounding conductors are sized to carry fault current safely long enough for protection to trip, and the size depends on how much fault current the path must carry. Transmission circuits carry much higher fault currents and have longer fault paths, so the equipment grounding conductor must be larger to handle that current without overheating. Distribution circuits have lower fault currents and shorter paths, so a smaller grounding conductor is acceptable. That’s why the minimum grounding conductor size for distribution is #2 AWG copper, while for transmission it is 2/0 AWG copper. The other options don’t fit standard practice because they would imply an oversized ground for distribution or an undersized ground for transmission.