How do I size motor starter transformers?

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.

delik2-------------@shaw.ca

On Fri, 08 Jul 2005 04:32:26 GMT, Frank White
<delik2----------------@shaw.ca> 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.
>
>delik2-------------@shaw.ca


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.