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You’ve got a full tank of air. The air tool ramps up nicely and is working well. Then, and as the pressure in the tank drops to the cut in pressure setting, rather than the compressor starting to rebuild the air in the tank, when it tries, the compressor trips the breaker on restart. If it’s a fuse in the circuit instead of a breaker, when attempting to restart, the compressor blows the fuse. The information on this page includes:
-what’s happening when the compressor trips the breaker or burns the fuse on restart?
-what needs to be checked on the air compressor when that happens?
-what are the compressor components involved and how to check them?
What’s happening when a compressor trips the breaker / fuse on restart?
When the air compressor tank is drained down to the cut in pressure level, the pressure switch reacts to the drop in tank pressure, it trips to “passing” (as in, the current now flows to the compressor motor) and the compressor should start and run until the compressor tank pressure has reached the normal cut out pressure setting, at which time the compressor should stop and wait for the tank air pressure to drop to the cut in pressure level again.
At the cut in pressure setting the the current will flow first through the pressure switch and then through the motor start circuit, and for a huge number of different makes and models of air compressor, the current then flows to a start capacitor.
If a particular compressor motor does not have a start capacitor, often that’s a small, sub-fractional motor, and there is sufficient current in the electricity flow to kick that motor into turning.
Larger compressor motors require a “kick start” to get going, as there is not enough power in the circuit to to feed what the compressor motor needs on start up, and that’s called the “inrush current”.
If for some reason the motor cannot start, it will continue to draw power, and may pull enough amperage to exceed the capacity of breaker or fuse and as a result the compressor trips the breaker or fuse on restart.
What are the things on the compressor to check when the air compressor trips the breaker or fuse on restart?
Did the unloader valve work? Sometimes the unloader valve fails, and as a result, some compressed air is trapped over the cylinder piston. That trapped air adds to the load the compressor motor experiences on start up, and that additional load may be enough to force the motor into pulling too many amps and popping the breaker, or blowing the fuse.
To test for this, unplug the compressor, open the tank drain and drain all the air out of the compressor tank (which you should do after every use of your air compressor as part of the regular preventive maintenance), plug the compressor back in and if your compressor has one, flip the ON/OFF switch to on.
If the compressor starts this time and the breaker doesn’t pop, that suggests that your air compressor unloader valve is not working properly, one of which made by Square-D is shown in the image above, and you need to either fix it or replace it. To be sure, shut off the compressor, drain the tank again, and try to restart it with an empty tank. If the compressor starts easily again, then it’s pretty much certain that it’s the air compressor unloader valve failure that is causing your air compressor to trip the breaker on restart.
Are you plugging the air compressor into a power bar or extension cord? Home use extension cords are notorious for throttling power, as is a power bar. You may be under powering your compressor motor, and the resulting overheated motor may be contributing to the breaker tripping when the compressor starts.
Leave the compressor to cool for 15 minutes or so, and then try plugging the air compressor power cord directly into a wall socket, preferably one that has a 20 amp breaker, and has no other electrical devices using power at the same time as the air compressor is trying to start.
If the compressor starts this time, and after you have used some air and the compressor successfully restarts when the tank pressure drops to the cut in pressure setting, then you’ve nailed down the problem.
As a general rule we suggest that you add air hose to get the compressed air to your work station as opposed to using an extension cord to move the compressor closer to where you want to use compressed air. Nothing gets damaged if it doesn’t get enough air through a long hose. On the other hand, electrical devices are overworked if their power supply isn’t up to what is required leading to electrical maintenance issues.
Is it the pressure switch itself that has failed? Less likely, but still possible, that your air compressor trips the breaker on restart can be cause by a pressure switch that has shorted out.
When the air pressure in the tank drops, a diaphragm inside the pressure switch moves, and ultimately, that moving diaphragm forces the points inside the pressure switch to touch, a circuit is made, and power flows to the compressor motor starting it, and driving the pump to pump more air into the compressor tank.
Turn off or unplug the compressor.
Drain the compressor tank and then close the drain.
With due regard to the presence of live terminals inside the pressure switch, pull the cover off, reset the breaker, and watch inside the pressure switch to see if there is any arcing or sparking when you turn the compressor back on.
Since the pressure switch points should already be touching with the absence of air in the tank, there should not be any arcs or sparks, and if there are, that’s a pretty good indication that you pressure switch may be the problem.
You will need to replace the pressure switch.
Has the compressor capacitor failed?
If the compressor has a start capacitor, or a start / run capacitor, or two capacitors, the failing of one may mean that the compressor will blow a fuse or circuit breaker when attempting to start.
This is what a typical motor capacitor will look like:
The correction of the problem of when the air compressor trips the breaker on restart becomes increasing complex once these earlier tests have been made. One of the more complex tests is that of testing the capacitors.
Compressor motor windings shorting? In our opinion the next component that will be suspect when the compressor trips the breaker on restart are the motor windings shorting, or any of the electrical connections inside the motor that may be shorting and the sudden flow of electricity to ground pulls too many amps.
If you have reached this state in your compressor problem diagnosis, and you are not skilled in electrical motors or electrical circuitry, we suggest that you get your compressor motor to an electrical motor shop for a load test to try and determine what, if any, part of the motor is shorting.
These are a few of the typical reasons why an air compressor trips the breaker on restart. If you have experience with other scenarios, why not share them with visitors using the comment box below? If you see a comment and you would like to add to it, please feel free.
It is always helpful if you identify the make and model of your air compressor in any post.