Electrical code Compliance - Undersizing conductors for oversized rotary phase converter?

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Undersizing conductors for oversized rotary phase converter?

Andrew Thomas

2005-06-17, 11:31 pm

Hi,

I need three-phase power@home to drive loads which I presume have low
power factor rectifier/capacitor power supplies, such as lasers.
Although I probably won't ever need more than 10Kw, in consideration of
the power factor and also because in the world of surplus motors larger
is often cheaper, I bought a 60HP motor with a 140A 230V nameplate
rating (brand new, $300) to serve as the basis for a rotary phase
converter.

I believe code says I must size my single-phase conductors for %250 of
the 3 phase nameplate rating. I think that would require a service upgrade.

Is this a "hard" requirement? If I udersize my protective devices to
match service availability, would that be "OK"? I'll probably be running
it up with an auxilliary starter motor (cheaper (surplus) than the huge
capacitance required, from what I can tell) so start-up current
shouldn't be an issue.

-Andrew

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