Table saw switch wiring problem

[David Pascoe]

My magnetic switch for Delta Unisaw finally gave out after 24 years. I ordered a new one that won't arrive for ten days. That's too long to wait, so I went out and bought a double pole, single throw simple switch, wired it up and fully expected the saw to start. To my consternation it didn't. There is power across the poles so I've no idea why unless there is something about wiring a 220V switch that I don't know. I probably know just enough to be dangerous, but this seems very straightforward. I got black/black, white/white, green/green. What else is there?

Motor was replaced 3 years ago. Last week when mag. switch failed to start, breaker did not trip, no burnt wires or terminals in switch box, but contact points look like they do when they melt and stick closed, bright metal.

[Dan Friedrichs]

How do you know it was the magnetic switch that failed, and not the motor?

You are correct that you should just be able to hook the SPDT switch up and make it work. If it's not working, I'd get a voltmeter and confirm that you have the correct voltage on the correct terminals of the switch. If so, then you have a motor problem.

BTW, it's a bad idea to use a "regular" switch for a motor load, because when the motor shuts off, the collapsing magnetic field produces a large voltage which can arc across switch contacts and weld them together, potentially leaving the switch "stuck on" with no way to shut the motor off. They do make "motor rated" mechanical switches, and you should only use a motor-rated switch (and ensure that the rating of the switch meets or exceeds the size of the motor), even for temporary use.

[lowell holmes]

You might change it to 120 volts temporarily to see if it will run.

[David Pascoe]

You might change it to 120 volts temporarily to see if it will run.

How do I do that?

How do you know it was the magnetic switch that failed, and not the motor?

I don't, but I have to start somewhere and since this motor is only 3 years old and is never overloaded (I make boxes) I've no reason to suspect this Leeson 3hp, 240 vac motor. One morning I turned the saw on and it didn't start. There were no warning signs that anything was wrong. I took the mag switch apart and found the contacts in bad shape; one shows slight signs of wire insul. melting.

Man, this is a real kick in the head. I broke my back replacing that motor and got a hernia. Cabinet saws really suck when things go wrong. Can't even get to the start capacitors. But now I'm partly disabled and there's no question of replacing motors . . . I got a big fat anchor in my shop.

BTW, doesn't the switch contain thermal overload protection? I read somewhere that that was the whole point of the complexity of the switch, along with auto start protection.

[Rich Riddle]

I hate to ask this question, but are you certain power is getting to the motor? If so, how? And use and abuse don't have everything to do with electrical problems. I replaced a starter on a standby generator this morning. The generator has 273 hours of use, hardly anything.

[David Pascoe]

If its sitting outside, that is everything. Called corrosion. I'm a retired yacht surveyor so I've seen a lot of corroded gensets. Their problem is mainly disuse (Use e'em or lose 'em)

I only know that power is coming out of the switch. The wire conn. to the motor is unreachable. If anything, I would think that only the start capacitors could have been damaged by a shorting switch and I know of no way to test those. I think there would have to be some burnt external wiring for there to be any motor internal burning. As it is, there is less than 1/4" of melted wire insulation within the switch, where a wire connects to a fried contact point. That just isn't enough to extrapolate that to a fried motor, tho I suppose I could be wrong.

I think my next step should be to check the start capacitors. I'll need to pull the table top to get to the capacitors but the saw is built into a large center work island and all that has to be dismantled. I'm getting too old for that sort of thing.

[Dan Friedrichs]

Those contacts look a little rough, but I'd personally just rub some sandpaper on them and put the switch back together. Doesn't look irreparably damaged.

Damaging a motor is actually pretty hard. You'd have to overload it to the point that the enamel on the motor windings melted, and the magnetic starter often contains an overload protection to prevent that. But the centrifugal switch, start capacitor, or run capacitor (or any combination of those) could be bad.

I think your magnetic switch may be fine and there is something wrong with the motor.

PS - the pictures of the contacts are an excellent example of why motor-rated switches are required. Look at the huge surface area of those discs and the huge distance between them. A "regular" light switch has much smaller contact points spaced much closer together. The magnetic switch also contains a spring to make sure the contact "snap" apart as quickly as possible.

[David Pascoe]

Dan, the switch is toast. One contact arm is burned through and the points have nothing left to file smooth. I've got a replacement on order.

Motors like this are indeed hard to damage, which is why I can't believe a faulty switch could damage it when the switch is designed to prevent that. And a ground fault should have tripped the breaker, if not the switch. (Its a GFCI breaker).

I managed to get to the start capacitors which appear in good condition and have power at all terminals, four on one, two on the other, although I don't suppose this proves they are still good, only that they are passing current and that I have power to the motor. How much is another matter. There is no hum when I throw the simple switch.

[Ken Combs]

When you say the have power to the motor, can you be a little more specific?

Assuming this is a 240v setup, have you confirmed 240v across the two legs, 120 on each?, I've seen a two pole breaker fail on one terminal only.

[Ken Combs]

I just saw your earlier post regarding making a change to the 240v circuit. What was the change?

[David Pascoe]

When you say the have power to the motor, can you be a little more specific?

Assuming this is a 240v setup, have you confirmed 240v across the two legs, 120 on each?, I've seen a two pole breaker fail on one terminal only.

I can't reach the wire connections to the motor but I got 120 on each leg coming out of the switch AND power to the start capacitor. Despite its impossible location I removed the capacitors (start & run). When I accidently touched the terminals of the start capacitor I didn't get shocked, so I put the meter on it after discharging it and got a barely discernible reaction. That is in no way a fair test but it definitely throws doubt on it. I need to go out and buy a meter with a capacitance function. If I'm lucky, a bad capacitor is the root of my problem. On the other hand I may have just made the situation worse when the wire to the capacitor inside the motor came off. A spade connector, I can't see where it is within the motor somewhere on the back side. If I can't see it, I can't reconnect it.

[John Lanciani]

I can't reach the wire connections to the motor but I got 120 on each leg coming out of the switch AND power to the start capacitor...

But are you 100% certain that you have 240 volts between the two poles on the line side of the switch? The fact that you said that the problem started immediately after you made wiring changes strongly points to an error made there. It is highly unlikely, though possible, that there was a failure within the saw coincident to the other work being done.

Edited to add; I swear that when I read this yesterday you mentioned making changes to the incoming circuit but that information is now gone. Did you edit that info out?

Edited again; I found this in your other post on the same subject; http://www.sawmillcreek.org/showthre...t=#post2652827

"I had to make an alteration to my 240VAC circuit and disconnected it. When I reconnected the circuits, my Delta tablesaw would no longer start."


You definitely need to back up a few steps and reassess the work you did on the circuit before you dig any deeper into the saw.

If we knew where you are located I'm sure that one of us would be happy to lend a hand. If you're in central MA I would be happy to help.

[Charles Lent]

Your first picture shows that your starter switch is a 4 pole switch with 3 of the 4 pole contacts damaged. The 4th and undamaged pole is part of the low current control circuit so I would not expect any damage on it. With the other 3 poles being damaged it appears to me that your motor is a three phase motor. Trying to replace this starter with a 2 pole switch is not going to work. Are you trying to run this 3 phase motor on the single phase 240 volt power that's found in most home shops? It won't ever work without a VFD or rotary phase converter to make 3 phase power to run it. Yes, you need a new motor starter, but it needs to be for a 3 phase motor, from what I see, and you can't run this motor from single phase power without a phase converter of some sort ahead of it.

Before going any further, read the label on the motor to find out if it is one phase or 3 phase and it's operating voltage requirements. Post a picture of the motor label if you can. Do you have 3 phase power where the saw is located now?

Charley

[Dan Friedrichs]

Also, your tests of the start cap are fishy. You are unlikely to get shocked from a start cap, since it was connected to AC (unlike a cap that was connected to DC, where some stored charge that zaps you is more likely). You also don't need a special meter to test a cap. Do you have a regular ohmmeter (continuity meter)? Put a wire across both leads of the capacitor to short it and discharge any remaining energy, then hook the ohmmeter up to the capacitor. The reading should initially be small and then rapidly climb to near infinity.

[David Pascoe]

I added a second 240 VAC line with another breaker to the panel. Had nothing to do with this circuit. The saw circuit was disconnected so that I could trace some wiring in the wall, nothing more. And no, I did not remove any posts. The 23 year old Delta switch simply wore out, the contacts burned and melted and blew the start capacitor. If it had anything to do with adding another line, I can't imagine what it is.

I'm having to pull the motor because when I removed the capacitors, the horribly limited access to the motor was such that I botched marking the wiring (all five wires are yellow) and although I can get a wiring diagram, I can't read it, so I'm taking it to a shop to get the capacitors wired correctly. I'm 70 y/o and it was just too painful to work under the saw and table.