Troubleshooting Magnetic Switches on Equipment

A cabinetmaker complains that a piece of equipment keeps shutting down for no reason. "Off" switches can be finicky, explain those who have had similar problems. March 1, 2006

I have a Delta Unisaw and it kicks off after running maybe five minutes or so, and the motor is not overheating. It doesn't even have time to get hot. I think the problem has to be the magnetic switch. Should I get another switch or try to adjust it? I sanded the points that touch in the switch and that didn't work. I noticed that there are a couple of different settings - one says auto-manual. What should I do?

Forum Responses
(Cabinetmaking Forum)
From contributor A:
Have you called Delta? In my experience, they typically will call back in an hour. Is there a warranty? Is it tripping the reset on the switch or the circuit breaker?

From contributor B:
If the saw is tripping off then the first thing I would look at is the off switch. In the magnetic starter the off switch is a normally closed (normally on) switch. If this loses contact, even for a split second, the motor will shut down. Also, on the newer switches there is a heater control. This is a rotary dial that should have some numbers on it, maybe 10-17. Turn this to the higher number area. It is like a variable amperage circuit breaker. Another thing to look at is a small sensitivity screw. This controls how sensitive the off switch is. Turn it and check the sensitivity of the off button. If it is touchy, you barely need to touch it to turn it off. If it is normal you need to push the switch in about a 1/4" to turn it off. Take the cover off the magnetic starter and operate your Unisaw and see if you still have problems. If you no longer have the problem, this is most likely the source of your trouble. I just went through this on my oscillating sander.

From the original questioner:
Let me give a little more detail on what it is doing. After running for about five minutes the saw kicks off and will not start back for about five minutes. Even then it will not start by just pushing the on button - you have to push the stop button sometimes twice then hit the start button. Five minutes later it kicks off again. The circuit breaker is not tripping - it is entirely in the switch. To answer the question about warranty, I bought this saw used and it is several years old.

From contributor B:
Here's what you do next. Go into the switch and disconnect the leads that go to the motor. Then activate the switch as you would normally. If it doesn't click off after 5 minutes it is working fine and the problem lies in the motor. If it does click off, it is in the switch. If it is a switch problem, maybe you can post a good close-up picture of the switch with its cover off so I can see what I'm dealing with.

From contributor C:
Be sure to blow it all out really well with compressed air. That is always my first move when I have trouble with a switch on a woodworking machine.

From contributor D:
Do you have dust control hooked up to the saw? My Unisaw behaved like this a couple of years ago before I had dust collection. I would just empty the saw when it was full. When mine acted up, I took the motor out, dismantled it and blew it out thoroughly with compressed air. I was amazed at how much dust was in the motor. Since then I've used dust control.

From contributor E:
Do as contributor B said - crank it up a couple of numbers, as some are set too light from the factory. Iím not sure how common it is, but I had same problem on a planer. It started after two months of use, maybe when the switch got broke in. It would kick out after 10 minutes of free wheeling under no load, but 2 clicks on the dial and itís never happened again.

From the original questioner:
After setting the adjustments like contributor B said, it hasn't kicked off anymore, knock on wood.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor F:
I too had a similar problem. It turns out one of the connections in the switch box was loose. The screw was tight (it had apparently spot welded itself), but the wire was not making solid contact. Check those connections thoroughly!

Comment from contributor G:
Take care with switches. I had a no-voltage release switch with a bit of a hair trigger. One day it came on all by itself, and I put it down to temperature change. I fixed it by opening it up and bending the metal lever, but it taught me to beware of sensitive switches. Make sure they have a reasonable amount of travel.