Unisaw Motor Problems

[Ron Kurzius]

I have a unisaw that wouldn't start yesterday, just hum. I tried to spin the blade but it was almost seized, so I pulled the motor off and took it apart. Both bearings were fine so I blew the dust out and put it back together. Everything seemed fine once reassembled so I ran it on the bench for a 1/2 hour and all seemed well.

This morning I put the saw back together and tested it half a dozen times including ripping some 2X stock and so I scratched my head and went on to something else, later in the morning I needed to use the saw and when I flipped the switch the blade jumped a little and then blew the GFIC. It will not run when hooked to the GFCI but the blade spins freely so nothing is seized. I ran a 50' wire to a non GFCI outlet and the saw works fine, well seems too.

What caused the motor not to spin freely before I took it apart and why would it work fine on the GFCI when I first put it back together and then an hour later not. I tested everything else on that circuit, radial arm, router they don't trip the GFCI. It is a 3/4HP Delta motor.

Thanks!

Ron

[Charles Lent]

Did you pinch a wire when you put it back together? It's very easy to do. Unfortunately, you are going to have to take it apart again to find out. If you find a pinched wire or a place on a wire where the insulation is damaged you will need to repair it. Several wraps of plastic electrical tape will do it or some shrink tubing, if the wire goes to a terminal and you can temporarily disconnect it.
Also check the condition of the starting capacitors and the wires to them. Then check the centrifugal starting switch. Make certain that the collar slides freely on the shaft. Clean the shaft if it is necessary. Also, check the contacts of the switch itself to see if it is in good shape. As the motor comes up to speed, the collar will move on the shaft and open the switch contacts to disconnect the start winding and one capacitor from the circuit. When the motor is shut off and slows down, the collar should move back and allow the switch contacts to close, readying the motor for the next time that it needs to start. If the switch contact fails to close as the motor stops, the next time you start it, it will just hum and trip the circuit breaker or the motor overload protector in the motor relay box. All of this needs to work correctly or you will have problems.

Since you just took it apart and then experienced the problem when putting it back together, I believe you pinched a wire so look for that first.

Charley

[Dick Strauss]

Did you check the arbor bearings?

[Mike Schuch]

The previous owner of my Powermatic 65 cabinet saw swapped the original TEFC 3ph motor out for an open frame 1ph motor. Every 50 to 100 hours of sawing I have to remove the cover plate on the motor and blow the saw dust out. Been doing this for 20 years now... it is just part of the saws character.

I find that your saw is blowing the GFCI outlet of great concern! Something isn't right! Either the ground wasn't reconnected or you pinched a wire or something when you reassembled the motor like previously mentioned. You really need to address this issue BEFORE you put the saw back in production! The GFCI is telling you SOMETHING IS WRONG!

[Ron Kurzius]

The previous owner of my Powermatic 65 cabinet saw swapped the original TEFC 3ph motor out for an open frame 1ph motor. Every 50 to 100 hours of sawing I have to remove the cover plate on the motor and blow the saw dust out. Been doing this for 20 years now... it is just part of the saws character.

I find that your saw is blowing the GFCI outlet of great concern! Something isn't right! Either the ground wasn't reconnected or you pinched a wire or something when you reassembled the motor like previously mentioned. You really need to address this issue BEFORE you put the saw back in production! The GFCI is telling you SOMETHING IS WRONG!

There is no doubt that it is telling me something but what? I have no idea. I'm not sure if you are familiar with this motor but there are no wires to be pinched and no ground, two wire only. Unless something happened to the winding when I took it apart there are no other wires that could be damaged. I removed the GFCI and replaced it with a regular outlet because I needed the saw. I ripped a couple hundred feet of 2X fir with no apparent damage, motor not hot and no smoke.

If there wasn't a gfci there I wouldn't even be thinking about this. I'm still baffled.

[Ray Newman]

No ground?? How old is this saw?

Also wondering if the GFCI could be faulty as the motor operates normally when you changed it out to a non-GFCI outlet??

[Frank Pratt]

Electrician here. If it is tripping a GFCI then that means there is current leakage to ground somewhere, which can be dangerous. Having no ground wire on the saw makes it especially so. You need to get that thing grounded NOW, before you even turn it on again.

That high resistance connection to the frame could at any time degrade into a low resistance. If that happens when there is no ground wire, the frame of the machine could become energized at line voltage. If I'm sounding alarmist, that is my intention. Please get that thing fixed.


Frank

[Ray Newman]

Rrank Pratt: need your insight -- do/can a GFCI could bad over time? I have heard that they can fail for no reason at all....

[Frank Pratt]

Yes they can go bad. Try plugging something else into it & see if it trips. But whatever the condition if the GFCI is, make sure you get a ground installed on the saw.