Control panel neutral size

[sndbodkin]

We installed a waste water lift station control panel. The panel has a 60 amp disconnect and controls two 240 vac 1 phase motors. The power is supplied to the control panel by a 100 amp 1 phase 240 vac breaker panel. The branch conductors feeding the control panel are 6 cu awg and are fed through a 60 amp 2 pole breaker. They neutral size is 12 awg. The neutral load in the control panel is milliamps that only connects to a 2.5 amp 24 vdc power supply.

The local inspector tells me that I need a neutral conductor capable of caring 60 amps to this panel based on 220.61a.

We have built and installed hundreds of control panels and we have never had an inspector require this.

 

[luckylerado]

I would have to agree. The feeder neutral needs to be sized for the max load regardless of actual load. I wonder if he would have said anything if the control transformer was 240V to 24V

 

[augie47]

I don't necessarily agree with his Code reference, but I would not accept a #12 based on 215.2 which requires a feeder neutral to be sized not less than the equipment grounding conductor.

 

[Smart $]

I'm leaning a little closer to the inspector's position, as Gus (augie47) says... you still need to size the neutral conductor not less than the minimum required feeder EGC. Fed by a 100A breaker, the minimum copper EGC is #8.

 

[texie]

We installed a waste water lift station control panel. The panel has a 60 amp disconnect and controls two 240 vac 1 phase motors. The power is supplied to the control panel by a 100 amp 1 phase 240 vac breaker panel. The branch conductors feeding the control panel are 6 cu awg and are fed through a 60 amp 2 pole breaker. They neutral size is 12 awg. The neutral load in the control panel is milliamps that only connects to a 2.5 amp 24 vdc power supply.

The local inspector tells me that I need a neutral conductor capable of caring 60 amps to this panel based on 220.61a.

We have built and installed hundreds of control panels and we have never had an inspector require this.

It has always been a mystery to me why branch circuits for applications such as this don't have a clear requirement for minimum neutral size based on 250.122 as feeders do in 215.2(A)(2). After all, in a line to neutral short the conductor has to be large enough to be an effective fault return path to trip the OCPD. As Augie pointed out, I think the inspector is is calling the wrong citation though. I also don't believe that the neutral in this case needs to be full size as otherwise you could end up with a situation where the neutral of a feeder could end up being smaller than the branch circuit neutral it supplies.
Logic tells me that the neutral in your case would have to be a minimum of #10 per 250.122 in order to be able to safely trip the OCPD. I do think this is implied in the NEC but I'm not sure the code explicitly says this. I've often thought this should be addressed with new code language.
Let's take a more extreme example. What if your panel needed a 600 amp branch circuit and you had a small line to neutral load of, say, 16 amps. By your reasoning you could use a number 12 for the grounded conductor. Physics says that this will not be able to safely trip the OCPD in the event of a L to N fault.

 

[Smart $]

...
Logic tells me that the neutral in your case would have to be a minimum of #10 per 250.122...

I think you are basing the #6 on the ungrounded feeder conductor size and load end breaker... but those appear to be feeder tap conductors, and tap rules require the EGC to be sized by the OCPD rating at the supply end.

 

[texie]

I think you are basing the #6 on the ungrounded feeder conductor size and load end breaker... but those appear to be feeder tap conductors, and tap rules require the EGC to be sized by the OCPD rating at the supply end.

I thought you might catch this. I assumed 60 amp as the basis as when I re-read the OP I think he means he has a 60 amp breaker feeding his control panel that just happens to be installed in a 100 amp panel. I can see where you are coming from though, as initially I read it the same way, that it might be a tap.

 

[cloudibew]

Why not relocate the x-former into its own box and nipple in the ctrl v or go 240v on everything and remove of any acutal need for a x-former and a neut. but wouldnt it change things up if the control cabinet is engineered and/or ul listed as a device vs an assembly?

 

[Smart $]

I thought you might catch this. I assumed 60 amp as the basis as when I re-read the OP I think he means he has a 60 amp breaker feeding his control panel that just happens to be installed in a 100 amp panel. I can see where you are coming from though, as initially I read it the same way, that it might be a tap.

After rereading it, you may be correct. :slaphead:

 

[sndbodkin]

I don't necessarily agree with his Code reference, but I would not accept a #12 based on 215.2 which requires a feeder neutral to be sized not less than the equipment grounding conductor.

Thanks guys, It is interesting to read your responses. The feeder conductors actually terminate in the 100 amp breaker panel. The conductors that feed the control panel are branch circuits from that breaker panel fed by a 60 amp 2 pole breaker.

 

[sndbodkin]

Usually, when we install motor control panels, they are usually 240 or 480 3 phase and we install a control transformer and use that to feed the control power to all the control devises. The control panel is usually is fed by a branch circuit coming from a safety switch and we never bring a neutral only a ground with the branch circuit conductors. However, because this panel is 1 phase 240. I didn't see the need to install the transformer.