"Lew Hodgett" wrote in message
hlink.net...

Somebody wrote:
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.


"Al Reid" asks:

Are you sure about that one. All of the references I am aware of limit
the overcurrent device to 30A on a #10 wire.

Anyone know for sure?

It is all a function of the insulation used.

No, it's not. Theampacity may be higher than 30 A, but code limits the
evercurrent device to 30A. See the tables in section 310. Section 310
states that #14 = 15A, #12=20A and #10=30A. I agree that the rated
ampacities may, however, be greater than those limits.

My question is, can anyone cite the section of the NEC that allows a larger
overprotection that is stated in section 310?

I have never ran across that exception and I have been an Electrical
Engineer for 24 years working in, among other areas, electrical construction
engineering. I am still looking at the code book.



The function of the c'bkr is to protect the insulation on the wire, not
the
wire itself and most definitely not the motor.

Don't have my code book handy to verify; however, the use of a #10
conductor
on a 5HP/240V/1PH motor even if legal, would at best be considered a bad
installation.

The difference between the I^2*R heat losses of that #10 vs the lower heat
losses of a #8 would soon consume any material savings made during
installation.

After that, the power company would be laughing all the way to the bank.

Personally, I'd use #6 wire /w/ a 2P-40A c'bkr for a 5HP/240V/1PH motor.

SFWIW, have designed and sold the equipment to build more than a few
electrical distribution systems during my career.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the
Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures