Round up Rule Under 800A

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NClark

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There seems to be some confusion with 240.4 B with when and how it can be used. Specifically on service conductors. Many say it cant be used and many say it can. Article 230.90 A exception 2 states it can be used however 240.21C states the rule cannot be used on transformer secondary conductors, which all services essentially would be...

The question is; Do conductors feeding an electrical service originating from a utility transformer fall under 240.21 C?? If so it would conclude the round up rule cannot be used on services.
 
Yes it can be used for services. For non-dwellings 500 kcmil (380 amps) is a pretty standard conductor size for a 400 amp service. Same goes for #4/0 aluminum (180 amps) 200 amp service.

Welcome to the Forum. :)
 
up to 800A. Above 800A 240.4 C kicks in and the ampacity of the conductor must match the OCPD
 
xformer said:
IMHO...240.21(C) applies to service or feeder conductors after the service point. :)
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240.21(B) and the analogous section of 240.21(C), only concern conductors that are on the load side of the service disconnecting means in some form or another. Service conductors may "look like" they are governed by these sections, since they are ultimately are conductors that come off a transformer's secondary, but service conductors have their own rules that apply.

240.21(C) is for secondary conductors from a customer-owned transformer. Likewise, 240.21(B) is for taps branching from a feeder, where the feeder is already load-side of at least one disconnect on the premises.
 
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