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#209951 - 05/17/13 11:32 AM 3 phase feeder with only (1) 120 volt circuit  
sparkync  Offline
Member
Joined: Oct 2002
Posts: 829
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 12:10 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]  
sparkync  Offline
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Joined: Oct 2002
Posts: 829
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 ??


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


#209954 - 05/17/13 04:55 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]  
sparkync  Offline
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Joined: Oct 2002
Posts: 829
NC
No, there are (3) 3 phase motors, (4) 208/240 volt single phase motors, and (1) 120 volt single phase motor


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


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Joined: Jul 2004
Posts: 9,135
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

#209960 - 05/18/13 11:33 AM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]  
sparkync  Offline
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Joined: Oct 2002
Posts: 829
NC
Greg, if you don't mind me asking, how do you come up with this? thanks. I'm reading from 2011 Code.


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


Member
Joined: Jul 2004
Posts: 9,135
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

#209962 - 05/18/13 04:34 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]  
sparkync  Offline
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Joined: Oct 2002
Posts: 829
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


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


Member
Joined: Jul 2004
Posts: 9,135
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

#209983 - 05/20/13 12:24 PM Re: 3 phase feeder with only (1) 120 volt circuit [Re: sparkync]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 834
Michigan
Article 215
215.2 (A) 2
Grounded Conductor.


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