ATS with two WYE sources, unused neutral

[ShortCircuited140]

Hi,

I have an ATS that has a utility 480VAC WYE feed on source one and a generator 480VAC WYE on source two. The systems downstream of the ATS are all 480VAC and do not require a neutral. (some motors, delta primary transformers and power supplies).

The ATS in question is a 4 pole ATS, it is configured for 3pole no neutral. The neutral from utility and generator are therefore not connected to the ATS. Instead the electrician tied them both together in the panel and are further not connected to anything else. The utility 480WYE transformer neutral is bonded to ground at the transformer, the generator neutral is also bonded to ground at the generator. Summarized, ATS has two sources, both sources have L1, L2, L3 terminated on the ATS. Neutral of both sources are tied together on a lug in the same panel.

I believe both neutrals should be terminated on the ATS and kept isolated from one another due to the generator neutral being separately bonded to ground, even if downstream of the ATS nothing is connected to neutral.

Would like to hear ya'lls thoughts and if there is any NEC code that this violates.

 

[infinity]

The utility 480WYE transformer neutral is bonded to ground at the transformer, the generator neutral is also bonded to ground at the generator

Is the ATS also the service disconnect?

 

[electrofelon]

Hi,

I have an ATS that has a utility 480VAC WYE feed on source one and a generator 480VAC WYE on source two. The systems downstream of the ATS are all 480VAC and do not require a neutral. (some motors, delta primary transformers and power supplies).

The ATS in question is a 4 pole ATS, it is configured for 3pole no neutral. The neutral from utility and generator are therefore not connected to the ATS. Instead the electrician tied them both together in the panel and are further not connected to anything else. The utility 480WYE transformer neutral is bonded to ground at the transformer, the generator neutral is also bonded to ground at the generator. Summarized, ATS has two sources, both sources have L1, L2, L3 terminated on the ATS. Neutral of both sources are tied together on a lug in the same panel.

I believe both neutrals should be terminated on the ATS and kept isolated from one another due to the generator neutral being separately bonded to ground, even if downstream of the ATS nothing is connected to neutral.

Would like to hear ya'lls thoughts and if there is any NEC code that this violates.

Your neutral conductor must be run to the service equipment. Where is the service disconnect, I assume that is the ATS? I would say that is not a separately drive system in the neutrals of both sources should be bonded together and to your grounding electrodes.

 

[ShortCircuited140]

Is the ATS also the service disconnect?

There are multiple service disconnects upstream between the ATS and the transformer as well as the generator and ATS. The ATS is not used as service disconnect.

 

[electrofelon]

There are multiple service disconnects upstream between the ATS and the transformer as well as the generator and ATS. The ATS is not used as service disconnect.

What you describe sounds non-compliant. The ATS must be the service disconnect. How far away are the other disconnects?

 

[infinity]

There are multiple service disconnects upstream between the ATS and the transformer as well as the generator and ATS. The ATS is not used as service disconnect.

So the utility supply to the ATS is just a feeder?

 

[electrofelon]

So the utility supply to the ATS is just a feeder?

I misread what he said, I thought he said the service disconnects were after the ATS, so everyone ignore my last post.

 

[infinity]

There are multiple service disconnects upstream between the ATS and the transformer as well as the generator and ATS. The ATS is not used as service disconnect.

And there is also a disconnect at the generator? If so then the neutral is not required for either feeder to the ATS.

 

[ShortCircuited140]

There is a 3 pole fused disconnect on each feed to the ATS on the same enclosure the ATS is in.

The service disconnect is located near the transformer and supplies more circuits than just this ATS enclosure. Correct the utility supply to the ATS is just a feeder.

 

[jaggedben]

I don't think the neutrals should be connected to each other if they are both bonded to ground. Either disconnect the neutrals from each other or disconnect the generator neutral from ground.

 

[ShortCircuited140]

What issues would arise if the neutrals remain connected and bonded to ground from both source locations?

 

[jaggedben]

What issues would arise if the neutrals remain connected and bonded to ground from both source locations?

Objectionable neutral current on grounded parts. Maybe not in this case if there are no line-neutral loads, but say if there are line-neutral loads upstream of the ATS or if they are added later. The code assumes there may be such.

What reason is there to bring the neutrals forward from the service disconnect or generator?

Btw your phrase 'same panel' in your original post is vague. I'm not quite sure what panel you're saying they were brought to.