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Thread: Boosting 208V to 240V

  1. #1
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    Boosting 208V to 240V

    I have a 150amp 120/208Y single phase panel that I need to boost to 230V.
    What size transformer(s) would be required to accomplish this? Would it be necessary to reduce the primary fusing and provide 150A fuses on the secondary? The panel is MLO.
    Thank you.
    John

  2. #2
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    What is the load that you will be feeding form this panel? A great deal more information will be needed before anyone can give you meaningful advice.

  3. #3
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    Quote Originally Posted by JES2727 View Post
    I have a 150amp 120/208Y single phase panel that I need to boost to 230V.
    What size transformer(s) would be required to accomplish this? Would it be necessary to reduce the primary fusing and provide 150A fuses on the secondary? The panel is MLO.
    Thank you.
    If you require the entire panel to be 120/240V 1PH 3W, you need to use a standard transformer, not a buck-boost one. 150A x 240V = 36kVA, so you would chose the next standard size of 37.5kVA. Yes, your primary OCPD should be evaluated considering the inrush characteristics of the transformer.

    If you actually need 230V Line-Line, do you care what your Line-Ground voltage is? If you can accept a L-G of 132V, you might be able to use a buck-boost arrangement.
    Just because you can, doesn't mean you should.

  4. #4
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    The panel serves general receptacle and lighting loads in a small office. Some computers, and an A/C unit rated 208-230V 30A. It was originally 208V 3 phase, but somebody screwed up and ordered a 240V single phase generator. Since there are no 3 phase loads we replaced the panel with a single phase. But the ATS won't transfer back to normal power because it only sees 208 volts, while it's looking for 240. We need to step it up to 240V (give or take) before it gets to the ATS.
    John

  5. #5
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    If all the loads are OK with line power at 120/208 and with generator power at 120/240, as appears to be the case, then I would simply fit a very small transformer to the ATS.
    Wire this such that when 208 volts is present from the utility, the ATS "thinks" that 240 volts is present and transfers back to line power.
    I would use a small isolating transformer of the type fitted in panels.
    208 volt primary and a 240 volt secondary. You may need to ground the center tap of the 240 volt secondary in order that is simulates a residential type 120/240 volt service with grounded neutral.

  6. #6
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    The pickup voltage on the transferswitch should be adjustable, so that problem can easily be fixed, if its on of the small Generacs the transferswitch is controled by the generator, and I have not had any issues with the single phase units not liking 208

  7. #7
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    Quote Originally Posted by broadgage View Post
    If all the loads are OK with line power at 120/208 and with generator power at 120/240, as appears to be the case, then I would simply fit a very small transformer to the ATS.
    Wire this such that when 208 volts is present from the utility, the ATS "thinks" that 240 volts is present and transfers back to line power.
    I would use a small isolating transformer of the type fitted in panels.
    208 volt primary and a 240 volt secondary. You may need to ground the center tap of the 240 volt secondary in order that is simulates a residential type 120/240 volt service with grounded neutral.
    That's an excellent idea. Thank you.


    Quote Originally Posted by hillbilly1 View Post
    The pickup voltage on the transferswitch should be adjustable, so that problem can easily be fixed, if its on of the small Generacs the transferswitch is controled by the generator, and I have not had any issues with the single phase units not liking 208
    It's a Kohler. It doesn't like the 208, and it doesn't seem to be adjustable
    John

  8. #8
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    I haven't installed a single phase Kohler in a long time, the three phase units have adjustable pots on the transferswitch door, but I don't remember what the single phase t-switch looks like. As broadgage posted, a small 208/240 transformer should work if you can separate out the voltage sense leads. I don't think the switch monitors the 120 volt connection, so it should not be needed.

  9. #9
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    " It was originally 208V 3 phase, but somebody screwed up and ordered a 240V single phase generator. Since there are no 3 phase loads we replaced the panel with a single phase. "


    I hope someone did their due diligence and confirmed there were no mwbc with 3 circuits sharing one neutral. I can't imagine any 3ph panels, feeding lighting and receptacles that didn't have at least some mwbc home runs. Changing one from 3 phase to single phase would require some homework in that regard for sure.
    Brian H. " No, I think you mis-understood. I said I'm an electrician, not a magician."

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