Sears air compressor throws breaker

What size breaker in on that line? 5h/p is a large motor.>

I was given an old Craftsman AC a few years ago that gave me problems. Upon inspection I discovered the ground and neutral wires had been reversed. Fixing this stopped the GFI from tripping but it tstill tripped the breaker till I ran a 20 amp circuit.

How cold is your shop? Does the compressor have 30W oil or 20W? (default is 30W, which may be too thick in the winter)

Bob

What size breaker is that on? A real 5HP motor will probably need a #10 circuit and probably would like a 40A breaker.

Chris

possession of a Craftsman model 919.165200, 5 hp, 20

Things that will cause the breaker to trip:

1. using an extension cord with the compressor.
2. other units running when the compressor kicks in.
3. bad or under rated circuit breaker. (need 15-20A)
4. a bad pressure switch on the compressor.
5. a bad capacitor on the compressor motor.
6. a bad motor on the compressor.

Bob

1. a bad unloader valve (maybe that's what you meant by the pressure switch)

Bob (no relation)

To many variables. What is the nameplate voltage and running amperage(fla)? Is the motor connected for 120 or 240 volts? Is the 20 amp circuit you're connecting it to, a dedicated circuit? Do you know that it is or was in working condition? Is the tank empty or is there compressed air in it?

If all else is up to par, that would be my guess as well

A compressor that size needs the motor set for 220 volts and 220 volt service plumbed to it to drive it. Even if it has a 120 volt setting, its foolish to run a motor that big on it. My craftsman in my garage is

Bob

compressor oil low? That will put a tremendous load on the motor.

Old breaker? Cycled too often? I would check if a true overload was happening.

Get an electrician, is shouldn't be expensive.

tom @

Yup. If the extension cord is too long the voltage drop will trip the breaker.

A single phase 5 HP motor at 115VAC draws 56 Amps. A single phase 5 HP motor at 230VAC draws 28 Amps. A five horsepower compressor is huge. Most garage 110VAC circuits are 20 amps at best. 230VAC circuits are usually 30.

You're all forgetting the funny way they rate horsepower on compressor motors. A "5 HP" motor might really be 2 HP or less.

My current 6 HP compressor runs on a 20A 240V breaker, and it doesn't put out as much air as the ancient 1.5 HP compressor that it replaced when the old one finally bit the dust.

Best regards, Bob

I've got a THREE QUARTER horse motor that is probably 45 years old, runs fine on a 15 a circuit, and is probably 2 1/2 times the diameter of these so called modern 5 horse motors. It runs my compressor all day continuously and will still be cool to the touch. (In cool weather that is, it's outside) They've really fouled up the electric motor horsepower ratings. I'd like to see one of these yuppifed motors on a motor dyno.

My 5hp/20gal compressor draws 15A.

-Bob S.

My CH compressor manual calls it a pressure switch. It's a pressure operated contactor that opens the ac line input when it gets to operating pressure. I once had a pressure switch go bad (weak spring & arcing contacts) and it would trip the breaker like the OP described.

-Bob S.