GEC size for 230.40 Exception #3

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Consider a single (or paralleled) 400A conductor set between a two gang meter without disconnects, and the weather head. After the meter, one 200A set feeds a 200A service disconneect in/at the structure the 2 gang meter is mounted to, and the other set feeds a remote separate structure and 200A service disconnect per 230.40 E3. Can the GEC at the first structure be sized to the KCMIL of the 200 amp set that feeds that structure's service disoconnect or does it need to be sized to the KCMIL of the riser? I am leaning toward the latter.
 

Dennis Alwon

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Well tables 250.66 is based on the size of the service entrance conductors. The wire in the riser are considered service entrance conductors so IMO, the grounding electrode conductor should be sized based on the 400 amps.

fwiw, the grounding electrode conductor may be different based on the whether the riser has parralel runs or one set.
 
Well tables 250.66 is based on the size of the service entrance conductors. The wire in the riser are considered service entrance conductors so IMO, the grounding electrode conductor should be sized based on the 400 amps.

That is my thinking. It is tempting to apply the provisions in 250.64 (D), but the described situation does not meet the wording in (D).

fwiw, the grounding electrode conductor may be different based on the whether the riser has parralel runs or one set.

Right. The CM area of a single set would be higher for a given ampacity than a parallel set so it could bump you up into a higher "tax bracket"
 
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