High Leg

[kwired]

I never understood why we don't have language in Art. 210 similar to 215.2(A)(2) for the cases where a piece of equipment needs a limited neutral for whatever reason. It would seem obvious that if this is done, as in the OPs case, that it needs to be a least as large as an EGC. But maybe you are right, it needs to be full sized except for the exceptions. But that seems crazy to me.

I just don't see it being required to be any larger then max load served. In the OP's case max load served by the grounded conductor is just a few VA @ 120 volts. I would understand if they said no smaller then 250.122 requirements, but they don't mention it at all for branch circuits.

I have ran 14AWG neutral several times for such cases - 240 volt three phase motor - with 120 volt contactor for control-no separate control transformer. Usually on aeration fans for grain storage bins - many not listed units either:roll:. I would rather run the 14 AWG then tie the control to the EGC like I have seen many others do. In fact sometimes I need to lift the neutral conductor from a grounding lug in these non listed units

 

[Smart $]

Read 210.20, especially (B), but note the general statement and consider the neutral is a branch-circuit conductor. The exception I mentioned earlier for household cooking appliances is the only alleviation that I'm aware of.

If you put an OCPD in the starter on the ungrounded side of the control circuit, the neutral would be protected, but then one can argue that the neutral from the panel is a tap conductor and not permitted under 210.19.

 

[delectric123]

I just don't see it being required to be any larger then max load served. In the OP's case max load served by the grounded conductor is just a few VA @ 120 volts. I would understand if they said no smaller then 250.122 requirements, but they don't mention it at all for branch circuits.

I have ran 14AWG neutral several times for such cases - 240 volt three phase motor - with 120 volt contactor for control-no separate control transformer. Usually on aeration fans for grain storage bins - many not listed units either:roll:. I would rather run the 14 AWG then tie the control to the EGC like I have seen many others do. In fact sometimes I need to lift the neutral conductor from a grounding lug in these non listed units

So what was the ampacity of the 3 ph. circuit? Wouldn't the 14 awg neutral be without proper overcurrent protection?

 

[GoldDigger]

So what was the ampacity of the 3 ph. circuit? Wouldn't the 14 awg neutral be without proper overcurrent protection?

If it were not for the single phase control loads, there would be no current on the neutral other than fault current.
I think this may come back to the difference between short circuit protection and overload protection.
If the three phase load is wired in delta, only line to ground faults can occur, not line to neutral. The EGC needs to be larger than #14.

 

[Smart $]

If it were not for the single phase control loads, there would be no current on the neutral other than fault current.
I think this may come back to the difference between short circuit protection and overload protection.
If the three phase load is wired in delta, only line to ground faults can occur, not line to neutral. The EGC needs to be larger than #14.

OP'er didn't state the size of the ground.

The neutral is #14. Line to neutral faults can occur in the supply run to motor starter.

 

[GoldDigger]

The neutral is #14. Line to neutral faults can occur in the supply run to motor starter.

But very likely to be near bolted faults rather than 2-5x overloads

 

[Smart $]

But very likely to be near bolted faults rather than 2-5x overloads

Depends on which conductor you are referring to. Bolted per neutral could be considered 2-5x the ungrounded conductor and ocpd... that is, until it is cleared by the ocpd, or the neutral evaporating?which could then cause a line-to-line or -ground fault.

 

[kwired]

OP'er didn't state the size of the ground.

The neutral is #14. Line to neutral faults can occur in the supply run to motor starter.

So say I run two circuits in a raceway, one with a 100 amp three pole breaker to protect a motor circuit and one with a single pole 15 amp breaker for a convenience receptacle near the equipment with the motor. With that logic that 15 amp circuit should have conductors sized to 250.122 just in case we ever have a cross connection between the 15 and 100 amp circuit, especially the grounded conductor? NEC is not written to cover that, and it is not generally done that way. I've pulled many heavy motor circuits up grain elevator legs, anywhere from 10 hp to 100 hp for the leg motor, and almost always a pair of 12AWG in same raceway to put a convenience receptacle up there as well.

I can kind of see the logic of a grounded conductor of a feeder needing to be minimum of 250.122 because it may have a greater risk of needing to carry the necessary current to interrupt the feeder protective device. I would also accept 250.122 if it were specifically mentioned for branch circuit grounded conductors, especially for a case like the OP has, but it is not mentioned. All I have found so far is that it must be able to carry the connected load - which is just a few VA for a contactor coil.

We are not permitted to provide overcurrent protection to grounded conductors - with exception of multipole breakers that open all circuit conductors simultaneously. Grounded conductors are inherently protected from overcurrent by not being connected to too much load. A fault from a conductor of another circuit is not a consideration required by NEC, or we would be doing multiple circuits in a raceway or cable differently then we are. A fault to ground on this conductor is not tripping an overcurrent device either, GFCI's yes, overcurrent devices no.

 

[Smart $]

So say I run two circuits in a raceway, one with a 100 amp three pole breaker to protect a motor circuit and one with a single pole 15 amp breaker for a convenience receptacle near the equipment with the motor. With that logic that 15 amp circuit should have conductors sized to 250.122 just in case we ever have a cross connection between the 15 and 100 amp circuit, especially the grounded conductor? NEC is not written to cover that, and it is not generally done that way. I've pulled many heavy motor circuits up grain elevator legs, anywhere from 10 hp to 100 hp for the leg motor, and almost always a pair of 12AWG in same raceway to put a convenience receptacle up there as well.

I can kind of see the logic of a grounded conductor of a feeder needing to be minimum of 250.122 because it may have a greater risk of needing to carry the necessary current to interrupt the feeder protective device. I would also accept 250.122 if it were specifically mentioned for branch circuit grounded conductors, especially for a case like the OP has, but it is not mentioned. All I have found so far is that it must be able to carry the connected load - which is just a few VA for a contactor coil.

We are not permitted to provide overcurrent protection to grounded conductors - with exception of multipole breakers that open all circuit conductors simultaneously. Grounded conductors are inherently protected from overcurrent by not being connected to too much load. A fault from a conductor of another circuit is not a consideration required by NEC, or we would be doing multiple circuits in a raceway or cable differently then we are. A fault to ground on this conductor is not tripping an overcurrent device either, GFCI's yes, overcurrent devices no.

Definitely a point of contention... but as you say, not covered by Code.

 

[Ryan88]

So the poco came out to test their lines and determined everything was good on their end. When we went in the electric room we smelled that distinct elect burning smell. Poco shut down the building. After some investigating we determined that they lost the neutral underground from main service to poco line. It was picking up the neutral from the subpanel in the mechanical room. Almost backfeeding for lack of a better term.

 

[kwired]

So the poco came out to test their lines and determined everything was good on their end. When we went in the electric room we smelled that distinct elect burning smell. Poco shut down the building. After some investigating we determined that they lost the neutral underground from main service to poco line. It was picking up the neutral from the subpanel in the mechanical room. Almost backfeeding for lack of a better term.

The subpanel itself will not provide a "neutral". The load(s) connected to it can create some voltage stability though. The more load there is and more balanced across the neutral it is the more stability you will experience, as you are kind of building an autotransformer with the connected loads, make some loads inductive and connect them line to neutral and it acts even more like an autotransformer.

Any neutral to ground bonds via the subpanel or connected loads will help with neutral voltage stabilization though they are not supposed to be there.