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Thread: 30kva 3phase step up transformer

  1. #21
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    4,391
    Quote Originally Posted by Ingenieur View Post
    op said the machine (saw) draws 80-125 A and it is 400 vac
    his ??? how to size the prim/230 side
    if he knew it drew 80-125 on the prim why ask?

    I did say the power seemed high ~ 100 A at 400 vac ~ 75 hp
    I did not find the kw til afterwards and since it was in Italian was not sure what it represented

    edited
    Agreed, he did write the saw, not the xfmr primary, was 80/125. I think he is in error based on all the math.

    The xfmr could be 'built-in', thus saying 'the saw requires 80A' would be the same as saying 'the xfmr requires 80A'. The saw motor requires ~34A, supplied by the as-built-in xfmr?

    mgraws post above sums up my thoughts. Primary OCPD 125Amp, #4 Cu primary conductors from panel to xfmr, #8 off the secondary to the motor (which may already be installed if the xfmr is sold and installed with the saw frame/chassis) . If secondary protection were needed, a breaker ~ 70A seems about right. OP would be wise to consult the mfg as that saw is a six-figure piece of equipment.
    Electricians do it until it Hertz!

  2. #22
    Join Date
    Nov 2009
    Location
    Opelousas, Louisiana
    Posts
    568
    Quote Originally Posted by JFletcher View Post
    Agreed, he did write the saw, not the xfmr primary, was 80/125. I think he is in error based on all the math.

    The xfmr could be 'built-in', thus saying 'the saw requires 80A' would be the same as saying 'the xfmr requires 80A'. The saw motor requires ~34A, supplied by the as-built-in xfmr?

    mgraws post above sums up my thoughts. Primary OCPD 125Amp, #4 Cu primary conductors from panel to xfmr, #8 off the secondary to the motor (which may already be installed if the xfmr is sold and installed with the saw frame/chassis) . If secondary protection were needed, a breaker ~ 70A seems about right. OP would be wise to consult the mfg as that saw is a six-figure piece of equipment.
    My guess would be the transformer is not in the saw but was supplied by the saw manufacturer. I would also guess the 80amp and 125 amp max ocp was also given by the saw manufacturer. My third guess would be the op is not familiar with transformers and didn't know how to size the wiring and overcurrent protection. We have all been there before.

  3. #23
    Join Date
    Sep 2008
    Location
    UK
    Posts
    10,528
    Pratch appears to have left the building.
    Si hoc legere scis nimium eruditionis habes.

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