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Thread: single phase 120/240 generator on 120/208 three phase system

  1. #1
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    single phase 120/240 generator on 120/208 three phase system

    So can it be done? Say one needs a generator with auto transfer for some small line to neutral loads (or even L-L if the loads are ok with either 208 or 240). I dont see any issue from an electrical theory standpoint, but the hangup I come up with is the transfer switch accepting different voltages. Do any have this capability? There is a pretty big price jump going up to three phase genny and transfer switch.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  2. #2
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    The 3Ø ATS will likely see 'phase loss' on genny and fail to transfer.

  3. #3
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    Might work if you set up the target loads on a 120/208 1Ø 3W panelboard and put the ATS between the 3Ø source and this panelboard.
    I will have achieved my life's goal if I die with a smile on my face.

  4. #4
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    Quote Originally Posted by chris kennedy View Post
    The 3Ø ATS will likely see 'phase loss' on genny and fail to transfer.
    If you did this you would likely have "select loads" and would have a single phase feeder supplying them from "normal power" Main issue would be if the line loss monitoring will be ok with 208 normal vs 240 standby power. I'm guessing many do not even monitor standby voltage though, if so this might not be a problem at all, as long as you can adjust the single phase transfer switch to accept the 208 nominal as an acceptable normal input voltage.

  5. #5
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    Quote Originally Posted by Smart $ View Post
    Might work if you set up the target loads on a 120/208 1Ø 3W panelboard and put the ATS between the 3Ø source and this panelboard.
    Yes, that is the hypothetical plan. I'm going to dig thru some transfer switch literature and see what the parameters are for the accepted utility voltage.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  6. #6
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    If you had 120 volt voltage monitoring on each line to neutral the unit won't care if it is 208 or 240 line to line. Don't know what is common to see for voltage monitoring on such units though.

  7. #7
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    Quote Originally Posted by kwired View Post
    If you had 120 volt voltage monitoring on each line to neutral the unit won't care if it is 208 or 240 line to line. Don't know what is common to see for voltage monitoring on such units though.
    Just taking a quick look at the generac RTS line:
    "utility voltage drop out - <60%"
    "utility voltage pick up - >80%"

    So that would work with 208 if that means what I think it means. I would want their blessing before trying it though.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #8
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    Quote Originally Posted by electrofelon View Post
    Just taking a quick look at the generac RTS line:
    "utility voltage drop out - <60%"
    "utility voltage pick up - >80%"

    So that would work with 208 if that means what I think it means. I would want their blessing before trying it though.
    Yeah, I'd want their blessing too. Had a brief glimpse at the general spec's and none are stated up front as being for 120/208 1Ø 3W.
    I will have achieved my life's goal if I die with a smile on my face.

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