What size grounding electrode conductor do I need?
Size it from Table 250.66 off your largest ungrounded service conductor. There is one shortcut worth memorizing: the part of the conductor run to a single ground rod, pipe, or plate never needs to be larger than 6 AWG copper, no matter how big the service. For the rest, read the table by service size.
Last reviewed June 2026 · Answered by JourneymanIQ staff
Start with the service conductor
Table 250.66 sizes the grounding electrode conductor by the largest ungrounded service-entrance conductor. Bigger service conductors mean a bigger electrode conductor.
Know the rod, pipe, and plate cap
Per 250.66(A), the portion run to a made electrode like a ground rod need not exceed 6 AWG copper. That single rule answers a lot of exam questions in one step.
Watch the parallel and aluminum notes
For parallel sets, size off the equivalent area of the largest conductor. Aluminum service conductors shift you to the aluminum column. Read the table notes, they change the answer.
Table 250.66 by service size, but to a ground rod it never tops 6 AWG copper.
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