Fire Pump Neutral

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Npstewart

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Good afternoon Everyone,

I am helping a friend out with question, any help would be appreciated.

We have a dedicated 277/480 wye service for a fire pump only. The service is dedicated for the fire pump & its controller only.

The service is being shown right now with a neutral conductor which isn't really serving any purpose and is basically just landing in a bus in the controller.

My question is: Is the neutral permitted to be reduced to a smaller size than the phase conductor? I am thinking this would fall under 220.61

PS> We are still under 2008 code.
 
If you have a grounded system you must have a grounded service conductor brought to the service disconnect. It must be sized to carry maximum load that may be connected to it but can not be smaller than the required grounding electrode conductor. I don't think the fact that it serves a fire pump changes anything.

See 250.24(C)
 
I second Augie's comments. Of course there is not much there to agree with. This is no different that you installing a grounded service to anything with a main disconnect. The NEC requires the neutral to installed up the the main for a fault current return path.
 
What about 220.61 where it says:

"(C) Prohibited Reductions. There shall be no reduction of
the neutral or grounded conductor capacity applied to the
amount in 220.61(C)(1), or portion of the amount in (C)(2),
from that determined by the basic calculation:
(1) Any portion of a 3-wire circuit consisting of 2 ungrounded
conductors and the neutral conductor of a
4-wire, 3-phase, wye-connected system
(2) That portion consisting of nonlinear loads supplied
from a 4-wire, wye-connected, 3-phase system
FPN No. 1: See Examples D1(a), D1(b), D2(b), D4(a),
and D5(a) in Annex D.
FPN No. 2: A 3-phase, 4-wire, wye-connected power system
used to supply power to nonlinear loads may necessitate
that the power system design allow for the possibility
of high harmonic neutral-conductor currents."


Is this not saying that a reduction isn't permitted?
 
Npstewart said:
What about 220.61 where it says:

"(C) Prohibited Reductions. There shall be no reduction of
the neutral or grounded conductor capacity applied to the
amount in 220.61(C)(1), or portion of the amount in (C)(2),
from that determined by the basic calculation:
(1) Any portion of a 3-wire circuit consisting of 2 ungrounded
conductors and the neutral conductor of a
4-wire, 3-phase, wye-connected system
(2) That portion consisting of nonlinear loads supplied
from a 4-wire, wye-connected, 3-phase system
FPN No. 1: See Examples D1(a), D1(b), D2(b), D4(a),
and D5(a) in Annex D.
FPN No. 2: A 3-phase, 4-wire, wye-connected power system
used to supply power to nonlinear loads may necessitate
that the power system design allow for the possibility
of high harmonic neutral-conductor currents."


Is this not saying that a reduction isn't permitted?
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I would say that if you performed the basic calculation you would end up with 0 amps on the neutral. As Kwired pointed out and since you have no neutral current you could down-size it to the minimum GEC size.

Pete
 
pete m. said:
I would say that if you performed the basic calculation you would end up with 0 amps on the neutral. As Kwired pointed out and since you have no neutral current you could down-size it to the minimum GEC size.

Pete
Click to expand...

I agree. The conditions that are listed in Npstewart's post are for when the neutral will be equal to, or greater than, the phase currents.
 
I really appreciate everyone's help on this.

I did notice though that a couple people mentioned a service disconnect however there isn't a disconnect in this project. Its going from the transformer, directly into the controller. I know that doesen't change anything but just wanted to clarify.

As always, thanks!
 
Npstewart said:
I really appreciate everyone's help on this.

I did notice though that a couple people mentioned a service disconnect however there isn't a disconnect in this project. Its going from the transformer, directly into the controller. I know that doesen't change anything but just wanted to clarify.

As always, thanks!
Click to expand...

FWIW, most (if not all) fire pump controllers I have seen were listed as suitable for use as service equipment and they had a disconnecting means.

Pete
 
Hopefully you will find that the controller is "Service Rated". A number of Fire Pump controllers are. If not, you and the inspector may have an "opportunity"
 
augie47 said:
Hopefully you will find that the controller is "Service Rated". A number of Fire Pump controllers are. If not, you and the inspector may have an "opportunity"
Click to expand...
I'm pretty sure that a SUSE label is part of the UL listing of an electric fire pump controller. I have never seen one that was not SUSE labeled. It's just a label, but it does also imply a neutral landing lug. Technically if you state that you have a delta service you don't need it, but most mfrs don't charge extra to remove it. :roll:

And yes, I agree on the neutral conductor sized the same as the EGC, there is no load on the neutral.
 
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