Circuit Breaker

[Brett]

What size circuit breaker would you recommend for a :
10HP 3PH Compressor?
a 15HP 3PH Compressor?
Will be getting a second hand one soon and want to organise the out let in anticipation

[MAC702]

Define "HP." Are you talking about TRUE RUNNING horsepower, or "max developed horsepower?" There is a BIG difference.

[Sandy]

There are charts which try to cover a broad range of motors and uses to come up with some usefull averges. They may not be exact for any paricular application but do get you in the ball park.

10HP 3PH run under load amps = 27 amps @ 230v and 14 amps @ 460v.

15HP 3PH run under load amps = 38 amps @ 230v and 19 amps @ 460v.

Keep in mind that if you had a motor that is truly 10 or 15 hp 'under load' it's start up current could be up to several times that.

I think what mac is alluding to is the fact that compressor manufacturers may not always be quite upfront (ahem) with some of their compressor motor specs. What they list as horse power leans a lot more towards 'peak developed' horse power than it does towards what they might be able to 'run' at for extended periods of time.

If a guy likes playing with these things, the above breakers should get you in the ball park. After that you could take an ampmeter amd do some tests under various start and run conditions to fine tune the breaker. Obviously start up with an empty tank isn't going to be quite as severe as start up at 125lbs or run at 60lbs will be slightly lower that run at 150lbs, things like that.

[Brett]

Thanks for the info Sandy and MAC 702