I cut and pasted from an old post to save typing. I've had no problems
with my setup.
I just finished wrestling with that very issue. I became the
unexpected owner of a 5 HP Single Phase Unisaw and had to figure out
how to wire it. In a phone call to Delta's technical people, they
1. Delta's 5 HP motor draws 100 Amps for about 1.5 seconds at
2. A 30 Amp "slow trip" breaker will hold it, but they are more
expensive and hard to find. (Home Depot never heard of 'em.)
3. A 40 Amp breaker will hold it fine, and that is what Delta
I sought advice from a couple of Electrical Engineers at work. They
assured me that:
1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only
feeding an electric motor that is hard-wired, AND there are no other
loads on the circuit.
2. It's not unsafe to run such a setup, because the motor's internal
overload switch will protect the motor itself. The only other
catastrophe would be a direct short, and the #10 wire will carry
enough amps to trip the 40 Amp breaker before the wire overheats.
The information presented above is hearsay. I am not a licensed
electrician, nor an electrical engineer. Check local codes before
installation. Void where prohibited. Your mileage may vary. Free
advice is worth what you pay for it.
My earlier post drew lots of flames from people who claimed to know the
code and that it can't possibly allow a 40 amp breaker on a #10 wire.
I looked it up and quoted the NEC extensively in a later post if you
want to google search for donkeyhody and unisaw. BUT, if you have an
inspector to satisfy, it may not be worth the trouble since it's an
obscure exception. HE may not be aware of the exception.
#8 wire is not that much more expensive, but I already had the #10
run, so it was worth checking for my application.
"We should be careful to get out of an experience only the wisdom
that is in it - and stop there; lest we be like the cat that sits down
on a hot stove-lid. She will never sit down on a hot stove-lid
again---and that is well; but also she will never sit down on a cold
one anymore." - Mark Twain