two transfer switches with one generator

[wireguru]

here's the scenario: one service supplies two panels. both panels to be fed from one backup generator. would transfer switches that switch the neutral be required? it seems as though if the neutral is not switched, then you have a #10 or whatever neutral connected between the two panels due to the common generator connection.

 

[steve66]

Does each panel have its own neutral to ground bond? Or is the N-G bond before the panels in a common disconnect or meter base?

If there is only one N-G bond, then there's no need to switch the neutral in the xfer switch.

If there are two N-G bonds, then things get a little more complicated. I'm not sure if a switched neutral would be required or not.

Steve

 

[wireguru]

Does each panel have its own neutral to ground bond? Or is the N-G bond before the panels in a common disconnect or meter base?

If there is only one N-G bond, then there's no need to switch the neutral in the xfer switch.

If there are two N-G bonds, then things get a little more complicated. I'm not sure if a switched neutral would be required or not.

Steve

if there is only one NG bond ahead of the panels, and there are two transfer switches (or breaker interlocks) without the neutral switched, then there is a second neutral path between the two panels caused by the generator wiring. Is that ok? I thought it wasnt.

 

[steve66]

With 3 pole transfer switches, the generator is not considered a separately derived source, and there should NOT be a bond between the neutral and ground in the generator.

If there is only one N-G bond, there won't be multiple neutral to ground paths.

 

[hillbilly1]

There is a possibility of circulating currents due to both panel neutrals would be paralelled where they connect at the generator. This could be a problem if the panel neutrals are vastly different in size (say one is sized for 400 amps, the other for 60 amps) and the load is unbalanced. Not a great possibility, but still possible.

 

[wireguru]

There is a possibility of circulating currents due to both panel neutrals would be paralelled where they connect at the generator. This could be a problem if the panel neutrals are vastly different in size (say one is sized for 400 amps, the other for 60 amps) and the load is unbalanced. Not a great possibility, but still possible.

what if the panel neutrals are the same (200 amp panels) but the generator neutrals are only #10. You end up with a #10 between the two 200a panels.

 

[steve66]

There is a possibility of circulating currents due to both panel neutrals would be paralelled where they connect at the generator. This could be a problem if the panel neutrals are vastly different in size (say one is sized for 400 amps, the other for 60 amps) and the load is unbalanced. Not a great possibility, but still possible.

You would only have a problem with parallel neutrals if there are more than 1 Neutral to Ground bond.

With a 3 pole transfer switch, there shouldn't be any N-G bond at the generator. No N-G bond at the generator, no parallel paths.

 

[wireguru]

You would only have a problem with parallel neutrals if there are more than 1 Neutral to Ground bond.

With a 3 pole transfer switch, there shouldn't be any N-G bond at the generator. No N-G bond at the generator, no parallel paths.

how so? wouldnt current flow for example from panel B on the generator neutral supplying panel B, through wherever the generator connections for each panel are tied together, then through the generator neutral serving panel A to panel A neutral bus, and from there back to X0 on the transformer

 

[mbeatty]

You would only have a problem with parallel neutrals if there are more than 1 Neutral to Ground bond.

With a 3 pole transfer switch, there shouldn't be any N-G bond at the generator. No N-G bond at the generator, no parallel paths.

I agree with Steve66 that you would not have a parallel neutral path as long as there is only one neutral to ground bond and no N-G bond at the generator.
Regards,
Mark