National Electrical Installation Standards

Standards as High as Your Own

Monday, March 5, 2018


Hi and Peace to you, well there is always some installation practices that seem to arise. I have my thoughts on what the code says, really like to hear what you say the code states. Can one use a green THWN insulated equipment ground run with URD in a trench (direct buried) (feeder or even branch circuit) or even connected to a concrete encased electrode? What if the outer jacket is removed and only the bare copper wire is now exposed to the direct buried elements? I see 310.10 (F), 250.118&119,300.5 coming into play and maybe the white book. Will look forward to your code answers. Thanks.

Butch Gosselin



Hey Butch thanks for your question, there are multiple possible answers. Conductors that are directly buried must be identified for that use as stated in 310.10(F). In general wire type equipment grounding conductors can be bare, covered or insulated as stated in 250.118(1). Bare aluminum equipment grounding conductors are not allowed to be in direct contact with masonry or the earth, or be terminated within 18 inches of the earth, as stated in 250.120(B). But that restriction does not apply to copper conductors. Similar rules for aluminum grounding electrode conductors are in 250.64(A). It is very common to use either bare or insulated copper grounding electrode conductors underground where connected to grounding electrodes. Bare copper conductors are also used as grounding electrodes in 250.52(A)(3) and 250.52(A)(4).

Equipment grounding conductors installed underground for agricultural buildings must be insulated as stated in 547.5(F). So, if not at an agricultural application then is seems copper equipment grounding conductors should not be an issue underground whether they are bare, covered or insulated. Make sure the AHJ agrees and there are no local restrictions. An exception to 310.10(F) that allows bare or covered wire type equipment grounding conductors underground would make the rules clearer in the future.

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