3 pole vs. 4 pole Transfer Switches

[AZJeff2013]

Currently designing a hotel that will need a 208v/3 phase generator. The generator is feeding 2 transfer switches, one for the 3 phase fire pump and one for the 3 phase, 4 wire emergency panel. I am confused as to whether I want a 3 pole non-separately derived system or a 4 pole separately derived system. I have been reading 250.30 over and over and my head hurts. Any guidance is much appreciated!


Jeff
Southern Illinois

 

[ron]

Since it is 120V L-G, you don't require GF protection, which is one of the big drivers to choose to switch the neutral for accurate detection.
Since you will not have GFP, you can pick 3 pole switches for both and bond the N-G at the utility only and the gen would not have a N-G bond.
No need to bring the neutral over to the fire pump ATS from any source.

 

[LarryFine]

Right. Either there is one N-G bond on the load side of the TS, or there is one for each of both sources on the line side of the TS, never both.

If you have the former, you don't switch the neutral, thus a 3P TS; if you have the latter, you do switch the neutral, thus a 4P TS.

 

[ron]

Right. Either there is one N-G bond on the load side of the TS, or there is one for each of both sources on the line side of the TS, never both.

If you have the former, you don't switch the neutral, thus a 3P TS; if you have the latter, you do switch the neutral, thus a 4P TS.

Just a clarification, since there is no reason to waste money to bring a neutral to the fire pump ATS, only to the ATS for the EM Panels, you put the N-G bond at the utility source in this case, not on the load side of the fire pump ATS because there is no neutral there to bond together to ground at the transfer switch. I guess you could put the N-G bond on the load side of the EM Panel ATS, but that would be confusing to the AHJ and future operations staff I would think.