New jointer motor burnt up

[Jack Hoying]

I bought a new Delta JT360 6" jointer (3/4 hp motor) last month and have used it occasionally since then. Last night, I edge planned a piece of wood and then went to the tablesaw. I noticed a little flash and a small pop and figured a lightbulb blew out. When I was done sawing, I turned around and was surprised by a cloud of smoke rising from the jointer. I ran over and unplugged it and things settled down. The smoke seemed to be coming from the starter capacitor. I called Delta customer service this morning and they were very nice and said they would ship me a new motor yet today, with very few questions asked. I removed the motor this afternoon and took the cover off of the capacitor. Fluid ran out as I removed it and there was evidence of overheating. I'm not sure, but it looks like the capacitor wasn't insulated good enough and bare metal from it came in contact with the motor housing and burnt a small hole in the capacitor. Maybe some electrical types could figure out if that could of caused the problem. This all happened with the switch turned off, which is pretty scarry.

Jack

[Mike Henderson]

I'm going to assume that the motor is a 110 volt motor. In the 110 volt circuit, only one wire (black) is actually "hot" - the white wire is attached to ground at the main box.

In a properly wired system, the jointer will have a polarized plug with one prong larger than the other. The larger prong should attach to the white wire in the jointer. And I sure hope that you have a three prong plug on the jointer and didn't cut off the ground connector. If your outlet is properly wired, the white wire will be attached to the larger connecter in the outlet and the black wire will be attached to the smaller.

If the jointer is wired correctly, the switch will break the black wire circuit (it would be better if it broke both sides) so the power should have been turned off when you turned off the switch. If things were backwards, and the non-hot circuit was broken, it could leave power connected to the motor, and cause the smoke you experienced as power flowed from hot to ground.

The first thing you should do is purchase one of those test devices that electricians use to test whether the outlet is wired correctly. Make sure that all your circuits are wired correctly and for good measure change the outlets to GFCI outlets. GFCI saves lives!

Next, check if the switch on the jointer breaks the hot circuit when it is turned off. Even better, see if you can get a switch which will break both sides of the circuit.

It may be, however, that everything is wired correctly and the motor was heated enough by your use to cause the smoke after you walked away from it.

Good luck!

Mike

[Jack Hoying]

Mike,
Thanks for the informative reply. It is a 110 volt motor and I'm going to guess that the outlet is wired incorrectly, with the hot on the wrong leg. I'll check that out tomorrow. The motor wasn't at all hot and it had only been run for 20 seconds or so.
Jack

[Jack Hoying]

After checking the outlet this morning, I did find that the positive and nuetral were switched. In this situation, the hot line went directly to the motor, so that is why the shorted capacitor continued to burn after the switch was in the off position. The ultimate cause is that the metal capacitor wasn't properly insulated and it grounded itself against the motor housing. If my outlet would of been wired correctly, it would only short out with the switch on, but it still would of happened.
The moral of the story is, buy an outlet checker at the hardware store and make sure your wiring is correct. That way, something like this won't happen when you aren't in the shop.
Jack

[Ken Fitzgerald]

Jack.....the metal cases on electrolytic capacitors are normally grounded.

[Ken Fitzgerald]

From further reading of your thread, the capacitor probably just shorted out. They do that occassionally and the fluid you saw running out was the dielectric escaping. If the capacitor shorted out and the outlet was wired incorrectly, it would provide a path for current....and thus the smoke! Good luck!

[Mike Henderson]

I'm going to make one more push for making all your outlets in the shop GFCI outlets. A GFCI outlet works by monitoring the current flow in the black and white wires. If the current flow is not equal, the GFCI trips. So in this case, if current flowed from hot to ground (not white) the GFCI would have tripped.

And, of course, when you touch a black wire and current flows through you to ground, the GFCI trips (and saves your life) - most of the time before you even feel the shock.

I don't know how to stress this enough - GFCI can save your life and could also prevent a fire in a situation like this. The cost of the GFCI is much less than either a fire or a funeral.

Mike

[Mike Henderson]

And if you have small children in your house, change all the outlets that are low to the floor to GFCI outlets. Anyone who has young children knows why.

Mike