Another 4 pole question

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e57

e57

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San Francisco, CA
So I got a panel with two feeders in, one parallel, and two loads out. One feeder is from a 480-208/120 transformer - the other from a 480-208/120 UPS. Do the breakers between the two need to be 4-pole?
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e57 said:
So I got a panel with two feeders in, one parallel, and two loads out. One feeder is from a 480-208/120 transformer - the other from a 480-208/120 UPS. Do the breakers between the two need to be 4-pole?
attachment.php
Click to expand...

Not enough info to say...

First question needing asked is, with a solidly-connected neutral configuration, is there a parallel path for neutral current? If yes, you'll either have to interrupt the parallel path somewhere and in a compliant manner, or use 4-pole disconnecting means.
 
Well it's yet to be built - and as spec'ed it would/could not switch the neutral.

The transformer is bonded I believe, and the UPS is rectified DC. As drawn it would have a solid connection on the neutral as well.
 
e57,
I will guess that with the step down of the voltage at the UPS, that it is a SDS so, suggest to the designer that 480V, 3ph, 3W into the transfer for both sources and serve a transformer on the output of the transfer.
 
ron said:
e57,
I will guess that with the step down of the voltage at the UPS, that it is a SDS so, suggest to the designer that 480V, 3ph, 3W into the transfer for both sources and serve a transformer on the output of the transfer.
Click to expand...

I'm getting the impression both the transformer and UPS serve the same loads... just not at the same time. Perhaps there already is a transfer switch upstream for the feeders, but to service either will require disconnection on the downstream side also.
 
e57 said:
Well it's yet to be built - and as spec'ed it would/could not switch the neutral.

The transformer is bonded I believe, and the UPS is rectified DC. As drawn it would have a solid connection on the neutral as well.
Click to expand...

If both the transformer and UPS have N-G bonding you have a parallel path for neutral current. One or the other will need to be unbonded or a 4-pole transfer means will be required.

The best approach is to remove the N-G[EC] bonds at each source and provide a single N-GEC bond at the panel under discussion... provided it is the first ocepd/disconnecting means downstream of the sources, and of course, meets the tap rules for transormer secondaries.
 
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Smart $ said:
I'm getting the impression both the transformer and UPS serve the same loads... just not at the same time. Perhaps there already is a transfer switch upstream for the feeders, but to service either will require disconnection on the downstream side also.
Click to expand...
My - you are intuitive.... To further complicate issues up-stream there is also a transfer sw for the XFR, and another transfer swtich for the proposed UPS, so both have the option of the same normal 480 buss - or the other generator fed one. These would then RECONNECT in the panel in question as well..... If we nail the job - there'll be a storm of RFI's on the grounding of the whole kitNcaBBootle. Since scope is limited to a UPS in a room...
 
e57 said:
My - you are intuitive.... To further complicate issues up-stream there is also a transfer sw for the XFR, and another transfer swtich for the proposed UPS, so both have the option of the same normal 480 buss - or the other generator fed one. These would then RECONNECT in the panel in question as well..... If we nail the job - there'll be a storm of RFI's on the grounding of the whole kitNcaBBootle. Since scope is limited to a UPS in a room...
Click to expand...

Sounds like the project needs a cluster of interlocked transfer switches!
 
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