Sizing the neutral conductor

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vanetten

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310.15(B)(6) states that the neutral service and/or feeder conductor can be smaller than the ungrounded (hot) conductors, provided the req's of 215.2, 220.22 and 230.42 are met. Is it okay to size the neutral service conductor the same size as the Minimum Service conductor?

The sizing of the service conductor is based on fastened-in-place appliances and other equipment utilizing a grounded conductor.

Most of the buildings that I provide service to do not have equipment specified yet. What happens if more equipment is added to the building later in time? Does the neutral conductor that was sized per equipment at the design stage have to be replaced later because the neutral conductor demand changed? Is there anything wrong with just sizing the neutral service conductor the same size as the minimum service conductor, as long as its not smaller than the required grounding electrode conductor specified?
 
Re: Sizing the neutral conductor

The only times that I have downsized the neutral is in residential work. Otherwise, with commercial, we always make it the same size as the ungrounded conductors.
 
Re: Sizing the neutral conductor

I'm not sure what you mean by the "minimum service conductor"?


Most of the buildings that I provide service to do not have equipment specified yet.
If the equipment is not specified yet, I don't know how you can size any of the service conductors. You can guess, but if you guess too small, they will have to be changed.

What happens if more equipment is added to the building later in time?
I think if the load exceeds the capacity of any of the service conductors (phase or neutral), they need to be changed and increased in size.

Is there anything wrong with just sizing the neutral service conductor the same size as the minimum service conductor
I think a load calculation needs to be performed for each service. If you are going to make the neutral smaller than the phase conductors, then you also need to calculate the maximum current that might be on the neutral. And that could be different for each service you do.

Steve
 
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