Single phase Generator

[sclarkdog]

I have a customer that has a 22kw generator with a automatic transfer switch 1ph he would like me to hook it up to his building that has 3 phase 120/208 3 ph. Is there a legal way I can install this.

 

[LarryFine]

Welcome to the forum.

Simply, no. Is he looking to power one 3ph load or a panel full of 1ph loads?

 

[hillbilly1]

One issue is, even if they are suppling a single phase panel, the generator control may see the 208 as under voltage, and may want to transfer not accept the utility voltages. Commercial transferswitches can be set to compensate for that, but the residential switches may be a fixed value. Have done it before with Genercraps, but all loads were 120 volt, so no issues of suppling 240 to 208 volt loads.

 

[ATSman]

Question 1: Is the generator 3 phase?
" 2: Is the ATS 1 ph or 3 ph ?
Some ATS units are 3 ph but are configured (wired) for 1 ph
so if it is a 3 ph gen and the ATS is 3 ph then yes, ATS just has to be configured and programmed for 3 phase
If the ATS is 1 ph then no
I find it hard to believe that a 22KW gen wound be 1 ph
so in that case you would need a 3 ph ATS to match the gen

 

[Little Bill]

Question 1: Is the generator 3 phase?
" 2: Is the ATS 1 ph or 3 ph ?
Some ATS units are 3 ph but are configured (wired) for 1 ph
so if it is a 3 ph gen and the ATS is 3 ph then yes, ATS just has to be configured and programmed for 3 phase
If the ATS is 1 ph then no
I find it hard to believe that a 22KW gen wound be 1 ph
so in that case you would need a 3 ph ATS to match the gen

There are plenty of 22KW generators that are 1 ph.

 

[ATSman]

ok tks, thats a new one on me as I don't work with 1 ph stuff

 

[kwired]

You can't supply (in any simple manner anyway) all three phases.

If you have certain loads you want to be backed up (no three phase loads of course) you could back up a single phase sub panel fairly easily. Any 208 volt loads will see 240 while running on generator. If all loads are 120 volts really not much for problems here.

As mentioned the controls possibly won't see 208 nominal as sufficient normal power and may not want to transfer back.

 

[LarryFine]

I just recently installed a Generac Guardian 24kw residential unit and ATS, all 1ph. The genny breaker is 100a.

 

[sclarkdog]

The generator & the transfer switch are single phase. He wants. To power up just single phase loads.

 

[augie47]

TO me the simplest solution would be to put the loads he wants on the generator in a single phase panel fed by the ATS but even then you need to watch for equipment rated 208v and for shared neutrals in the three phase panel, etc.
As Larry noted in Post#2 "no easy solution"

 

[hillbilly1]

I’ve had several customers want to do that to back up their computer rooms, the problem is if the UPS is 208, it will not like the 240 at all, so all of the UPS’s will have to be 120 volt input, or a single phase transformer on the utility side with a 120/240 UPS, by the time that is all done, it’s almost cheaper to put in a three phase generator and panel.

 

[ceb58]

One issue is, even if they are suppling a single phase panel, the generator control may see the 208 as under voltage, and may want to transfer not accept the utility voltages. Commercial transferswitches can be set to compensate for that, but the residential switches may be a fixed value. Have done it before with Genercraps, but all loads were 120 volt, so no issues of suppling 240 to 208 volt loads.

they usually have a set 80% voltage drop before they start and transfer for the home units so it should still be good with 208v.

 

[sclarkdog]

I guess I'm worried about a brown out that might be a safety issue. And is there anywhere in the code that talks about this>
Thanks for all the input

 

[kwired]

I guess I'm worried about a brown out that might be a safety issue. And is there anywhere in the code that talks about this>
Thanks for all the input

For optional standby systems pretty sure nothing. Legally required, don't think much from NEC but possibly from whatever code is behind needing a legally required standby system.

 

[rnatalie]

The Generac HTS transfer switch can be ordered either 208 or 240. It's not settable in the field. The utility "accept" is 85%.