DOWNSIZED NEUTRALS

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terry talbot

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houma, la
In part of out multi-parish jurisdiction one of our power companies is allowing and advising customers to downsize the neutral on services. ex. 200 amp service with 2/0 copper ungrounded conductors and 1/0 copper neutral at the service entrance. I understand that this was common practice at one time and realize that many existing homes have this arrangement but that it is not allowed by the N.E.C. any longer. Any thoughts?
 
ActionDave

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terry talbot said:
In part of out multi-parish jurisdiction one of our power companies is allowing and advising customers to downsize the neutral on services. ex. 200 amp service with 2/0 copper ungrounded conductors and 1/0 copper neutral at the service entrance. I understand that this was common practice at one time and realize that many existing homes have this arrangement but that it is not allowed by the N.E.C. any longer. Any thoughts?
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It is allowed by the NEC and is as common now as it was then. At least it is for me, I downsize the neutral every time unless someone tells me I can't.
 
roger

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terry talbot said:
In part of out multi-parish jurisdiction one of our power companies is allowing and advising customers to downsize the neutral on services. ex. 200 amp service with 2/0 copper ungrounded conductors and 1/0 copper neutral at the service entrance. I understand that this was common practice at one time and realize that many existing homes have this arrangement but that it is not allowed by the N.E.C. any longer. Any thoughts?
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Why do you think it is no longer allowed? See 220.61(B)

Roger
 
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terry talbot

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houma, la
I guess I wasn't clear. The power company is allowing the neutral to be downsized with no calculations. I realize that with known loads that this is allowed but there is a limit.
 
roger

roger

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Even with no calculations it would hard to imagine that the service neutral would have to be 85% of the ungrounded conductors ampacity which is what 1/0 is to 2/0.

And on another note, if this is under the control of the POCO it may not even be an NEC issue.

Roger
 
augie47

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ActionDave said:
You run into electricians quite often that believe a lot of screwy stuff.
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and inspectors.... :)

You are correct that there is no "automatic" reduction on a 200 amp service but it would be so rare for one not to be allowed if calculations were done that, in many areas, allowing a reduction without calculations has become standard practice.
When you think of the portion of the load on most home that is completely 240 (HVAC, water heater) plus those that are predominantly 240 (dryer, range), the neutral load is very low.
I have had E/Cs actually do the calculations and end up with a #2 neutral.
 
kwired

kwired

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NE Nebraska
Many places the inspectors will let you go two sizes smaller then the ungrounded conductors without bothering to ask for verification of loading.

If you have a situation where there is little or no neutral load at all - you must have at least the equivalent size of the required grounding electrode conductor as a minimum. For feeders it must be at least the size of the minimum required equipment grounding conductor if you have a neutral, feeders is possible to not have a neutral at all if there is no load utilizing a neutral conductor.
 
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