How do I size motor starter transformers?

Discussion in 'Electrical Engineering' started by Frank White, Jul 8, 2005.

  1. Frank White

    Frank White Guest

    I am looking for guidelines to help me size the control transformers
    for various magnetic starters. Size 00 to size 3 is typically for what
    I run into these days from Allen Bradley, GE, Square D, Westinghouse,
    etc.
    I cant seem to find too much data from the manufacturers. It seems
    that you need a higher VA rating to pull the mag in but once it is
    closed the power consumption is tiny. I have always erred on the high
    side because I have no specific guidelines.

    Any insight?

    Remove dashes "-----------" to e-mail.

    Frank White, Jul 8, 2005
    #1
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  2. Frank White

    Bob Guest

    On Fri, 08 Jul 2005 04:32:26 GMT, Frank White
    <> wrote:

    >
    >I am looking for guidelines to help me size the control transformers
    >for various magnetic starters. Size 00 to size 3 is typically for what
    >I run into these days from Allen Bradley, GE, Square D, Westinghouse,
    >etc.
    >I cant seem to find too much data from the manufacturers. It seems
    >that you need a higher VA rating to pull the mag in but once it is
    >closed the power consumption is tiny. I have always erred on the high
    >side because I have no specific guidelines.
    >
    >Any insight?
    >
    >Remove dashes "-----------" to e-mail.
    >
    >



    One rule-of-thumb that I always used when sizing for multiple coils
    was total sealed+ largest inrush. its a bit of an overkill, but it
    provides a margin of error that I was comfortable with. If it is just
    one starter, just size it based on the sealed VA and make sure you buy
    a Control Power Transformer (as opposed to a signal transformer or a
    potential transformer). CPTs are specifically designed up front to
    provide the inrush current you would expect from an AC coil.
    Bob, Jul 11, 2005
    #2
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