Breaker for motor question

[Unregistered]

I just bought a 5hp Leeson motor. Single phase. I looked through the Motor Design section of this site, but still have one question regarding breaker size. The detail plate says 20.6 amps at 230V. At 125% thats 25.75A. That means I can wire with 10ga and a 30 amp breaker. Correct? What got me confused it the 80% rule for breaker size. That put the total at just over 32A, meaning 8ga w/40A breaker. Which is correct?

Thanks

[mdshunk]

These "rules" you referred to are more like rules of thumb. For trouble free and code compliant operation, I use the following rule of thumb:

Match the wire gauge to the FLA rating of the motor. In your case, this is 20.6 amps, which would relate to #10 AWG.

Match the breaker size to 125% of the FLA rating of the motor or "max breaker size", if that is listed on the data plate; whichever is bigger. In your case, this is 25.75 amps (since no max breaker size is listed), which is a 30 amp breaker. The code allows you to upsize the breaker several hundred percent of the FLA rating of the motor, but it is a rare time when you have to go that overboard with the breaker size.

This sounds like it's perhaps an air compressor project, so you'll be a-o-k with #10 and a 30 amp breaker.

[Unregistered]

Actually, I'm going to experiment with using the motor to replace the worn out gas motor on my 20ton log splitter. I got it pretty cheap at a sale. Should make it ALOT quieter! Is a magnetic starter a good idea, or just a waste of money?

Thanks

[mdshunk]

If the motor doesn't have built in thermal overload protection, then you need to use a starter. The starter will provide the overloads necessary to protect the motor.