Two utility feeds switch neutral at second ATS

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W@ttson

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So I have two utility feeds feeding separate locations of a structure (structure separated by river). Usually utility 1 feeds only utility one loads and utility 2 feeds only utility 2 loads. Utility 1 has a backup generator, utility 2 does not. In the case that utility 2 loses utility from its own service, it should switch to the standby feed from utility 1 which can be the utility or the generator.

ATS 1 (where utility 1 and gen are) has a solid neutral connection

Does ATS 2 required a switched neutral per NEC?

See attached diagram.
 

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  • Neutral to Ground two utilities - switched neutral - Copy.pdf
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It will need to be a switched neutral not so much for the multiple neutral to ground but for the reason that they are two separate seperatly derived systems.
 
It's debatable whether or not it is required because the systems are separately derived prior to the service points... and the NEC does not cover separately derived services. I would switch them to avoid the parallel neutral current path [250.6]
 
In my view this would need to be a switched neutral to satisfy 250.24(5). While the OP did not indicate the voltage and amperage, there will also be issues with GFP if used.
This kind of setup is fairly common with, say, 2 buildings each with their own service and use a common generator for both.
 
In my view this would need to be a switched neutral to satisfy 250.24(5). While the OP did not indicate the voltage and amperage, there will also be issues with GFP if used.
This kind of setup is fairly common with, say, 2 buildings each with their own service and use a common generator for both.

The utility feeds at 208/120, but each feed into the ATS is 480/277 (there is a step up transformer which I omitted). I believe that since the utility itself is supplying at 208//120, no GFP is required?
 
In my view this would need to be a switched neutral to satisfy 250.24(5). While the OP did not indicate the voltage and amperage, there will also be issues with GFP if used.
This kind of setup is fairly common with, say, 2 buildings each with their own service and use a common generator for both.


I can buy the 250.24(5) reference requirement. Thanks, will make it a switched neutral.
 
The utility feeds at 208/120, but each feed into the ATS is 480/277 (there is a step up transformer which I omitted). I believe that since the utility itself is supplying at 208//120, no GFP is required?

OK, then if I understand correctly you essentially you really have 2 separately derived systems. But I think the problem is the same. See 250.30(A). And the GFP would only come onto play if 480 volt and 1000 amps or more.
 
In my view this would need to be a switched neutral to satisfy 250.24(5). While the OP did not indicate the voltage and amperage, there will also be issues with GFP if used.
This kind of setup is fairly common with, say, 2 buildings each with their own service and use a common generator for both.

I can buy the 250.24(5) reference requirement. Thanks, will make it a switched neutral.
Color me puzzled. Note, all 250.24 sub-paragraph references are 250.24 followed by an upper case letter (A thru E) and then a number if referencing a sub-sub-paragraph under (A) or (C)... and the only (5) there is, is 250.24(A)(5)...
(5) Load-Side Grounding Connections. A grounded conductor
shall not be connected to normally non–currentcarrying
metal parts of equipment, to equipment grounding
conductor(s), or be reconnected to ground on the load side
of the service disconnecting means except as otherwise permitted
in this article.
What does this have to do with switching the neutral? Are you guys saying the neutral-ground bond of the service not switched in is on the load side of the other, switched in service. If yes, the NEC doesn't view it that way as a service is a service is a service and it is never on the load side of a service. If no, please explain how (5) relates to this scenario.
 
Color me puzzled. Note, all 250.24 sub-paragraph references are 250.24 followed by an upper case letter (A thru E) and then a number if referencing a sub-sub-paragraph under (A) or (C)... and the only (5) there is, is 250.24(A)(5)...

What does this have to do with switching the neutral? Are you guys saying the neutral-ground bond of the service not switched in is on the load side of the other, switched in service. If yes, the NEC doesn't view it that way as a service is a service is a service and it is never on the load side of a service. If no, please explain how (5) relates to this scenario.

That is the (5) that I was assuming. 250.24(A)(5)

I guess the way I see it is that when you are on service A, you have a neutral and ground bonded by the service entrance in the service disconnect. If you look down stream and the neutrals are connected between the two services, you will have another neutral to ground connection (grounded conductor connected to normal non-current carrying parts). This is so because service B also has a neutral to ground connection at its service disconnect. Forgetting that is a service and the fact that the conductors inside the service disconnect at service B there is electrical continuity between the grounded conducted which service A is connected to and the grounding conductor of the system.

Since the services actually feed step up transformers and the output of the transformers are separately derived from each of the utilities, I guess it would be easier to see the requirement when looking at 250.30(A). This alleviates the notion of whether or not a service can be on the load side or not.

But to muddy up the waters, 250.24(A)(3) refers to dual fed (double ended) services which this is kind of like. It says that one connection from the grounded to the grounding conductor can be made at the tie point.

In any case, I think the best route is to switch the neutral.
 
typo

typo

In my view this would need to be a switched neutral to satisfy 250.24(5). While the OP did not indicate the voltage and amperage, there will also be issues with GFP if used.
This kind of setup is fairly common with, say, 2 buildings each with their own service and use a common generator for both.

My apologies guys. I meant to type 250.24(A)(5). Sorry for the confusion.
 
...But to muddy up the waters, 250.24(A)(3)...

In any case, I think the best route is to switch the neutral.
It doesn't muddy the waters as it points to the necessity of having only one neutral-ground bond in the connected system.
 
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