3 phase feeder with only (1) 120 volt circuit

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3 phase feeder with only (1) 120 volt circuit #209951
05/17/13 11:32 AM 05/17/13 11:32 AM

sparkync

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Joined: Oct 2002
Posts: 830
NC

I have a feeder feeding several Refrigerant motors. The total amperage after applying the 125% for the largest motor comes out to 93.42 amps counting 1 small cooler evaporator that is 120 volts that only pulls 4.73 amps. Is there any reduction of the neutral in a case like this or is it just applied over 200 amps? The rest of the load has no neutral. Thanks..

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Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209952
05/17/13 12:10 PM 05/17/13 12:10 PM

sparkync

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Posts: 830
NC

Also I have a 3 phase feeder. It's been a long time since I've figured up a 3 phase feeder. Do I divide the total amps by 3?? 93.42 (94 amps)/3= 31.33 ??

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209953
05/17/13 04:51 PM 05/17/13 04:51 PM

JBD

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Joined: Jul 2001
Posts: 599
WI, USA

Originally Posted by sparkync

Also I have a 3 phase feeder. It's been a long time since I've figured up a 3 phase feeder. Do I divide the total amps by 3?? 93.42 (94 amps)/3= 31.33 ??

Are they single phase motors spread equally across the phases, or are they 3-phase motors?

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209954
05/17/13 04:55 PM 05/17/13 04:55 PM

sparkync

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Posts: 830
NC

No, there are (3) 3 phase motors, (4) 208/240 volt single phase motors, and (1) 120 volt single phase motor

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209958
05/17/13 09:50 PM 05/17/13 09:50 PM

gfretwell

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Joined: Jul 2004
Posts: 9,337
Estero,Fl,usa

I read 220.61 as saying you could use a #14 for a neutral if your max neutral load is 4 or 5 amps.

Greg Fretwell

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209960
05/18/13 11:33 AM 05/18/13 11:33 AM

sparkync

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Posts: 830
NC

Greg, if you don't mind me asking, how do you come up with this? thanks. I'm reading from 2011 Code.

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209961
05/18/13 12:49 PM 05/18/13 12:49 PM

gfretwell

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Joined: Jul 2004
Posts: 9,337
Estero,Fl,usa

Quote

220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load
shall be the maximum unbalance of the load determined by
this article. The maximum unbalanced load shall be the
maximum net calculated load between the neutral conductor
and any one ungrounded conductor.
Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems,
the maximum unbalanced load shall be the maximum
net calculated load between the neutral conductor and any
one ungrounded conductor multiplied by 140 percent

I do not see anything that would make you use more than a #14 if the only unbalanced load is a 4 amp single phase motor.

In the computer room biz we never even brought a neutral beyond the service disconnect because there was never any unbalanced load. (everything was line to line)

Greg Fretwell

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209962
05/18/13 04:34 PM 05/18/13 04:34 PM

sparkync

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Posts: 830
NC

Thanks Greg. I just wanted to make sure there was not another rule I was missing in the code. I'll figure a bigger neutral just in case in the future they want to add something else that is 120 volts. In fact there is an old outlet attached to one of the units, that the owner said they wouldn't need, but now that I think about it, an outlet is required for "service means" on a roof top. Thanks again

Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync] #209963
05/18/13 05:53 PM 05/18/13 05:53 PM

gfretwell

Member

Joined: Jul 2004
Posts: 9,337
Estero,Fl,usa

If you serve that outlet from another phase, you are still OK with a #14 if it is a 15a circuit. (the way I read it)

I agree as a design issue, running a bigger neutral is probably a good idea.

Greg Fretwell