Air Compressor Blows Circuit
       Breaker When Running



My air compressor blows circuit when running. Why is that?

There are a number of reasons why an air compressor will suddenly blow a circuit or fuse in the electrical panel when the compressor is running. Here some are and the steps you can take to correct the problem.

Please note we are not talking about an air compressor that blows the circuit breaker or fuse in the panel when it is trying to restart. Diagnosing the compressor restart issue is covered here.

When a compressor is filling the tank with air, the compressor motor has to work harder and harder as the pressure in the tank grows. New air has to be forced past the tank check valve into the tank in order for the pressure to increase, and that increased load on the pump also means an increased load on the motor. Normally, if the compressor is working with the normal parameters, this does not pose a problem.

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That being said, what could cause an overload and a blown breaker or fuse in the panel?

Before you go down the path of checking the compressor itself, do yourself a favor and check the breaker in the panel. Is it in tight? Are the wires attached securely? Obviously, if you are not comfortable with working in the panel, don't do it yourself, but get an electrician to check. A loose breaker or wire connection could result in the breaker popping while the compressor is running. You might also have them check the breaker itself to make sure that it has not weakened over time and worn out.

Is Compressor Pump Oil Lubed?


If the compressor has been working well up to the point that the problem occurs, and if it is an oil lubed pump, a low oil condition in the sump would create friction related load as the pump overheated, that would increase the load on the motor, and could cause a blown fuse or breaker in the panel. So, check the oil!

Mechanical Cause of Circuit Blowing?


If the air compressor blowing circuit breakers is a new condtion, check to ensure that the belt (if one) is tensioned as recommended in the manual. A too tight belt increases load. Adjust as needed.

Check the alignment of the motor sheave to the pump sheave. Misalignment could increase load on the motor.

With the power off and the belt removed, rotate the motor shaft to ensure that it isn't jammed. Also rotate the pump sheave to check that there isn't binding inside the pump. Either condition could increase load and pull enough amperage to blow the fuse or circuit breaker.

Compressor Motor Failure?


By the nature and variety of compressor motors out there, this has to be a general advice section, and is typically aimed at single phase, 115 V motors, though the information applied generally to other compressor motors as well.

Compressor motors often have a start capacitor and a run capacitor. A failed run capacitor may result in a blown breaker or fuse at the panel. Often the cause of a failed run capacitor is heat. The motor nameplate should have a temperature value displayed, and if the temperature exceeds the high level, a failed run capacitor can result. See the page on this site about how to check capacitors.

That the compressor motor blows the electrical panel fuse or breaker while running may also indicate a wiring short. A small short may not appear when the motor is cold. After running for a while, particularly if the power supply is suspect, the electric motor will get very hot, the wires will expand, one touches, and there's now a short that causes the problem. This one is tough to diagnose, for sure. It may require taking the motor to an motor repair shop, getting them to test it under load, and paying for re-wiring if that's the cause.

Other pages on this site provide some basic checks for other compressor motor conditions. I hope that this page about why an air compressor blows circuit breaker when running brings some benefit. If you still have issues, use the forum linked below, and others will assist in time, I'm sure.