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Thread: Step Up Transformer

  1. #11
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    Quote Originally Posted by infinity View Post
    That's why I asked, since you only need to go from 240-277 and not 480 you should be able to find a suitable 1Ø transformer. If you were searching for 1Ø, 240-277/480 transformer I don't think that you will find one without going to 3Ø.
    Not off the shelf but you could have a 120 primary to a 480v secondary with a 277v tap custom wound

  2. #12
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    I presume that 240V is line-line, whereas 277V would be line-grounded conductor.

    If there are lots of separately switched circuits, then the transformer might make sense. If large banks are being turned on with the breakers or contactors then this is probably not a big benefit.

    -Jon

  3. #13
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    Quote Originally Posted by Andy Delle View Post
    Not off the shelf but you could have a 120 primary to a 480v secondary with a 277v tap custom wound
    Agreed. I don't see the problem.
    Si hoc legere scis nimium eruditionis habes.

  4. #14
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    Quote Originally Posted by Andy Delle View Post
    Not off the shelf but you could have a 120 primary to a 480v secondary with a 277v tap custom wound
    Which leaves you with 203 volts on the other side of the tap - should only allow using 58% of the transformer kVA rating also unless you are able to connect some lights as 208 volt loads.
    I live for today, I'm just a day behind.

  5. #15
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    Quote Originally Posted by Andy Delle View Post
    Not off the shelf but you could have a 120 primary to a 480v secondary with a 277v tap custom wound
    Why bother with the 480v winding if it's custom-made? I'd opt for 240v to 277v, whether standard, auto-transformer, or buck-boost.
    Code references based on 2005 NEC
    Larry B. Fine
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  6. #16
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    Quote Originally Posted by kwired View Post
    Which leaves you with 203 volts on the other side of the tap - should only allow using 58% of the transformer kVA rating also unless you are able to connect some lights as 208 volt loads.
    Yeah, I missed the 240v primary requirement. But then you could have a 240v to 480v with a 277v tap single phase xformer wound.

    MGM Transformer in Los ANgeles does custom winds. But then there is the subject of listing. Not sure is a custom design is listed even if the manufacture has UL certification.

  7. #17
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    Quote Originally Posted by Andy Delle View Post
    Yeah, I missed the 240v primary requirement. But then you could have a 240v to 480v with a 277v tap single phase xformer wound.

    MGM Transformer in Los ANgeles does custom winds. But then there is the subject of listing. Not sure is a custom design is listed even if the manufacture has UL certification.
    Do transformers need to be listed as a general rule? Some specific applications do.

    Doesn't matter what the primary voltage is, if you have a 480 secondary with a 277 tap - you only get 58% of the VA rating of the transformer from that 277 tap - might as well have gone with a 277 secondary to begin with unless you have a use for the remaining 203 volts on the other side of the tap.
    I live for today, I'm just a day behind.

  8. #18
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    Quote Originally Posted by kwired View Post
    Do transformers need to be listed as a general rule? Some specific applications do.

    Doesn't matter what the primary voltage is, if you have a 480 secondary with a 277 tap - you only get 58% of the VA rating of the transformer from that 277 tap - might as well have gone with a 277 secondary to begin with unless you have a use for the remaining 203 volts on the other side of the tap.
    Ok I see what you are saying.

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