Standby generator, 3 phase high leg

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mbam

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In getting ready for this year's hurricane season (S Florida) I am researching a standby generator. Assuming a proper disconnect/transfer switch are there any special considerations in addition to proper phase sequencing as a result of our service being 3 phase high leg? I know this is not code related, but I don't know of a better place to get the answer.

Thanks!!
 
Re: Standby generator, 3 phase high leg

You will have to test the system with the load being supplied by the generator. You may have to switch legs to get proper rotation. If it is a 240 system, be sure that the high leg is in the exact location in the transfer switch as the main panel (usually B phase at the panel) to prevent applying 190+ to 120v circuits.
Adjust the rotation by switching phases A and B (120v legs) under the load being supplied by the generator -if necessary.
 
Re: Standby generator, 3 phase high leg

Thanks, got that part figured out, just want to be sure the building won't care that the source is a 4 wire Y. I can't think of any reason it would matter.
 
Re: Standby generator, 3 phase high leg

You say your sevice is a Delta and the Generator is a Wye. Depending on the motors involved, (and other select items such as ranges) your starters and overload devices, as well as the motors themselves, may be a problem due to the lower voltage of the Wye.


Roger
 
Re: Standby generator, 3 phase high leg

What's on the high leg? Just A/C? Is the generator supposed to be able to run the 3 phase loads, or are you planning to just power lights and refrigerator? Are the 120V loads on a single phase panel or are all loads in the 3 phase panel?

If you don't need to supply 3 phase loads from the generator I'd use a single phase 120/240V generator. How to connect it depends on how your distribution is set up. I've converted 120/240V, 3 phase services to 120/208V, 3 phase power many times, but have never had two sources with different characteristics. If you plan to be able to supply the entire house be sure to use an transfer switch that switches the neutral and that is open transfer.

Martin
 
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