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#209951 - 05/17/13 09:32 AM 3 phase feeder with only (1) 120 volt circuit
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: 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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#209952 - 05/17/13 10:10 AM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: 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 ??

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#209953 - 05/17/13 02:51 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: 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?

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#209954 - 05/17/13 02:55 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
No, there are (3) 3 phase motors, (4) 208/240 volt single phase motors, and (1) 120 volt single phase motor

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#209958 - 05/17/13 07:50 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: 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

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#209960 - 05/18/13 09:33 AM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
Greg, if you don't mind me asking, how do you come up with this? thanks. I'm reading from 2011 Code.

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#209961 - 05/18/13 10:49 AM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: 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

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#209962 - 05/18/13 02:34 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: 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

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#209963 - 05/18/13 03:53 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: 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

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#209983 - 05/20/13 10:24 AM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
Article 215
215.2 (A) 2
Grounded Conductor.

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