changing a 3 phase MS to single phase

[Jon C.]

Hi,
I came across this job today. The previous electrician added a single phase manual transfer switch to a existing commercial 3 phase main service. They removed the high leg off the main disconnect, on the load side and ran the two legs and neutral to a 2 pole transfer switch. Now that the building is being remodeled, they are wanting to get new equipment, but the 3 phase has been disabled. They have a single phase 60 kva trailer mounted genset, so are reluctant to buy a new 3 phase generator.
I mentioned that there choices were to restore the 3 phase panel by adding the missing wire, if they want to use the single phase generator, install a new stand-by panel and run all the single phase loads into this panel and hook that up through the transfer switch.
I see this as a code violation, yet they claim the work was done by a licenced electrical contractor and inspected...
Any thoughts?
Thanks,
Jon

 

[starbolin]

Re: the current installation. Conceptually, if you have a red-leg system and you have no loads on the high leg then I can't think of any code that would require you to pull the high leg anywhere that it's not needed. ( The currents on a red-leg being not being balanced anyway. ) So, I think the installation is fine on that count. Though deficient on labeling of the high leg and the last guy should have bolted a dummy in the unused fuse spot.

Once the high leg is pulled with any existing wiring then the single phase transfer switch is a problem. Your proposed solution is correct. Tell the customer it's either that or a phase-converter and a 3P ATS. Either way I don't see how they are going to avoid re-pulling a lot of wire.

 

[Jon C.]

Re: the current installation. Conceptually, if you have a red-leg system and you have no loads on the high leg then I can't think of any code that would require you to pull the high leg anywhere that it's not needed. ( The currents on a red-leg being not being balanced anyway. ) So, I think the installation is fine on that count. Though deficient on labeling of the high leg and the last guy should have bolted a dummy in the unused fuse spot.

Once the high leg is pulled with any existing wiring then the single phase transfer switch is a problem. Your proposed solution is correct. Tell the customer it's either that or a phase-converter and a 3P ATS. Either way I don't see how they are going to avoid re-pulling a lot of wire.

Thanks for the reply. I had originally installed the service when I was a apprentice in the 80's, so I was not pleased to see that it was altered... The main expense for the customer is the new genset, so I think it would be better to go with a single phase sub panel, require the ATS to that.