3 phase feeder with only (1) 120 volt circuit

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..

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 ??

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?

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

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

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)

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

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.

Article 215
215.2 (A) 2
Grounded Conductor.

Thanks Yooper
I knew I was missing something but I just could not find it.
This is at the end of 215.2(A)(1)

Quote

The size of the feeder circuit grounded conductor shall not be smaller than that required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel.

This came in 2005

So if it cannot be smaller than the equipment ground required according to table 250.122, for a 125 amp breaker the minimum neutral would be #6 copper or #4 aluminum.

At this point you might want to consider not running a neutral at all and running a separate circuit for that one 120v load.