My craftsman 6hp 33gal compressor is tripping breakers, why?

Question

I picked this up cheap, and Im trying to troubleshoot.

It will turn on for a second, then trip the breaker. Or, I plugged in to where the garage door opener is plugged, and it turned on for a second, then stopped spinning and just heated the cord up.

I got a new start capacitor for it, but the old has a 220V on it. It appears to be the original Mallory, but this is supposed be a 120v 15 amp motor. Does this mean it was changed to 220? It still has a standard 120 plug, but a really thick cable. The motor itself says 120V on it.

What should I troubleshoot next? The centrifugal switch looks ok, it just never gets up to speed enough to open it.

Answer 1

Motor might be going bad, have you check whether it is drawing too much amps?

Answer 2

Motor probably going bad. Bad bushings/bearings throw armature off center towards the fields thus drawing excessive current and over amping causing breaker to trip. You can easily check this with an amp gauge. Having a higher voltage rating on the cap is ok. Just not to low such as a 120 cap on a 220 motor. With the belt off t6he motor check for any side play on the shaft. It takes very very little to make the motor no good, But again, take a reading with an amp gauge. The fact the cord heats up means it is pulling a lot of amps. Probably the reason you got it cheap.

Answer 3

what size breaker are you tripping sounds like that should be on a 20A circuit. if it a15A motor you are overloading a 15A breaker on start-up next check more into the motor

Answer 4

If you extrapolate NEC Table 430.248 (Full Load Currents in Amperes for Single Phase Alternating Current Motors) to approximate the FLC for a 6 HP motor (the Table jumps from 5 HP to 7-1/2 HP) you get a full load current for a 6 HP motor of 65.6 Amps at 120 Volts.

The motor should be opening the breaker before it even gets started, if you figure the current required to overcome the locked-rotor state (almost 400 Amps) - see Table 430.251(A).

There is no way a 6 HP motor will only draw 15 amps. [And, a 15 Amp load MUST be supplied through a 20 Amp circuit, with #12 AWG wiring.]

A 240 attachment plug will not have the same configuration as a 120 Volt plug; you could change the motor to 240 Volts, and cut these figures almost in half, if the motor is listed as dual-voltage. Check the name-plate on the motor.

Sometimes, there's a reason something has a low price.