settle an argument>> Can you still downsize neutral

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rt66electric

Senior Member
Location
Oklahoma
Here is the argument >> A fellow journeyman(old fart counting the days until he can retire to his future lakehouse)

Insists that you can downsize the neutral condctor. Refering to residential Main service entrance conductors. "you can reduce down two sizes"

I think this rule was eliminated sometime the late 80's

Loser buys breakfast.
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
For a 200 amp service you can downsize to the size of the gec, if the calculated load permits. Usually that is a number 4 copper conductor.
 

augie47

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Tennessee
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I think ya missed that the OP is talking about a neutral? which maybe to a 1/0 but never a #4
I'd say Dennis is correct... a #4 would normally be the minimum based on 240.42(C)/250.24(C). Be rare for the calculated load to allow, but legally possible.
 

hurk27

Senior Member
I'd say Dennis is correct... a #4 would normally be the minimum based on 240.42(C)/250.24(C). Be rare for the calculated load to allow, but legally possible.

sure if only there was no neutral load.


310.15(B)(6) The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met.
to use this reduction we must meet all three sections of the NEC mention above.

215.2 is for sizing feeders, so we can skip it.


230.42(C) points us at 250.24(B) which is the requirment to run a grounded circuit conductor to each disconnect for the purpose of a fault currnet pathway, hence the requirment of it being at least the size of the GEC.
This would be where the grounded conductor would not have a load.

220.22 which will allow a 70% reduction which for 200 amp is 140 amps, so table 310.16 a copper neutral conductor @ 75? will ba a 1/0,

220.30(A) Feeder and service-entrance conductors whose demand load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.22.
 

augie47

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Location
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State Electrical Inspector (Retired)
actually not "no load" but a calculated load of 85 amps.
That would allow a #4 to be used and meet the GEC size for a 200 amp service.
I don't recall seeing a 200 amp resid. service with a neutral load (calculated) of 85 amps, but, in answering the OP's question, a neutral reduction to a #4 would be possible.
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
Wayne, I stated that if the calculated load of the neutral was low enough then you could use a conducotr as small as a #4 for the grounded conductor. I stand by that-- thanks Gus.
 
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