Electrical Problems with a Bandsaw

      Most electrical problems are caused by loose connections, not bad parts. February 27, 2007

I've got a problem with my bandsaw that's really annoying and I could use a little help. I bought a used Delta 20" last summer which is only three years old now. It's a 2 hp 3 phase motor and I wired it up with the same disconnect box used in its previous home. The problem I have is that sometimes it won't start. Other times it starts up and works just fine. When it has one of its fits, it basically clicks and sounds like the motor is stalled for just a second, and then nothing. No reaction at all when you press the switch.

My first thought was a faulty switch, but upon opening it up I found some kind of circuit breaker and relay unit attached to the back of the switch. Delta has been no help with info on the circuit breaker, whether it needs to be adjusted or reset or replaced. It was like they didn't even know they were using these parts on their machinery.

So all I know is each of these parts is very expensive on its own, and I would rather not buy the wrong one, or both. If you have any suggestions before I have to hire a specialist to come in, I would love to hear them.

Also, I thought of just disconnecting the circuit breaker and wiring the switch directly, but the way they have it wired, it also goes through a relay, making things more complicated than they need to be, in my opinion.

Forum Responses
(Solid Wood Machining Forum)
From contributor F:
I am at a loss as to troubleshooting your problem from afar. But I can tell you how many times I have been afraid I had an expensive breakdown on a machine, only to fix it by blowing out the switch parts with compressed air.

Blow everything out really well, including motors and capacitors, before you bring in an electrician - you may be pleasantly surprised.

From contributor L:
The relay you have in the starter box is called a contactor. It is essentially a self-locking 3 pole switch. When you apply the sensor current to it, it pulls the main relay in. It also pulls a secondary relay in to keep the coil powered to hold the main contactor closed. If you have a brief power outage, the machine will shut down and not start up again until you press the start button. It should have a small wheel with numbers on it. Turn this wheel up to a higher number and try starting it. When a motor gets older it starts to draw more current at startup. This wheel is connected to the current sensor and is like a variable circuit breaker.

Make sure the start or stop buttons are not too close to the actual switching devices in the starter box. If the stop button is pressing on the stop switch inside the starter box, the machine will never start. Take off the cover and see if you can start the machine by pressing the same contact point that the start button presses. If this works, then you need to adjust the stop button so that it is farther away from the stop switch. This is usually just a screw attached to a metal clip that moves in and out to make the stop button longer or shorter. Disconnect the power and tighten all the screws in the starter box.

From contributor B:
You say it's a 2hp, 3 phase motor that you wired the same as in the previous home. Most homes don't have 3 phase power. So, my first question is whether you have this motor hooked up to single phase or 3 phase power. If it is single phase power, is there a static phase converter included?

From the original questioner:
Thanks - great advice as usual.

Contributor F, I took the switch out yesterday and gave it a good blow out, but there was not much dust in there. Good suggestion though, as I did have a problem with my planer last year that ended up being exactly what you described.

Contributor L, I'm going to take it back apart this morning. Now that you have given a little understanding of what may be happening, hopefully I can make it work.

Contributor B, I used the word "home" figuratively - the machine came out of a very large, very industrial building. My shop has three phase from the power company, so no converters for me.

One other thing I noticed when hooking this machine up, and have kind of forgotten about since, is the voltage differences in machines. The Delta motor is stamped as 230v where the disconnect it was wired up to someone (presumably the electrician) wrote 208v. I don't know what the voltage coming out of my panel is, as I don't have a multimeter handy. (I also don't really know how to check for voltage on three phase power.) But could different voltages cause problems? I do have another three phase machine I bought from the same shop which works fine.

From contributor B:
I have a good friend who makes his living doing industrial wiring... very heavy duty stuff. Years ago he told me that about 90% of electrical problems are mechanical in nature. That is, you are more likely to find a loose connection or something physically screwed up than a bad electrical part.

This guidance from him has proved useful to me time and again. As such, the first thing you should do, since the machine was moved, and if you have not already done so, is to tighten every wire connection you can find.

I fought my SCMI shaper for years with intermittent stopping. I replaced the overload sensor (much like a contactor, but trips from overload rather than a push button on/off switch) and even removed it from the circuit completely. I was totally convinced this was the problem. However, recently I had to deal with the intermittent stopping again and this time I went deep into the wiring looking at each and every connection. Low and behold, I found a connection on the internal breakers where the wire sheath was pinched into the wire clamp rather than just the stripped end of the wire. As such, under vibration, the stripped wire would occasionally lose contact and the motor would shut off. This was right from the factory and a problem I lived with on and off for many years!

So, take a look at all connections... especially any that could have been jostled during the move. Also, I'm pretty sure that for most 3 phase 230v sites, the voltage is 208. Your motor is almost certainly rated to work within that range.

From the original questioner:
Thanks. Isn't it funny how something as simple as a 2 cent wire coming loose can bring down machinery worth thousands? I poked around this morning with not much luck. I will check out the wiring this afternoon. The biggest problem is taking time away from jobs to play with this stupid machine. If I can't figure it out with another hour worth of wasted time, I think I'll bite the bullet and find a local technician. In the meantime, it looks like I'm back to re-sawing on the tablesaw.

From contributor F:
Don't forget this jingle:
"Loose wires start fires."

From contributor A:
Now I could be wrong about this, but the way it was explained to me years ago went like this. Three phase power is delivered in two forms, delta and wye, depending on the type of generating equipment or transformer used. 220 volt three phase was "wye" and you could use any leg with neutral to get 110 or any two legs to get 220 single phase. 208 volt was "delta" and you could use two legs to get 220 single phase, use one of two legs and neutral to get 110 volt single phase, use one of the two legs and the delta leg to get 208 volts single phase or use the delta leg and neutral to get 208 single phase. Or use all three legs to get 220 three phase. All I can tell you for sure is not to use the delta leg if you want to run 110 volt stuff - this will fry it fast.

The 208 should work fine with your 220 or 230 volt supply. Check the heaters to see if one needs replaced. They can get quirky and start heating up and cutting out sometimes, but it's usually consistent - heat up and quit, manually restart after cooling off and it will run again for about the same time with the same load. The heaters are located at the base of the contactor, one for each hot leg of the circuit, or three in your case.

My best advice is to learn how the contractors work, check on the internet and you will find plenty of sites. Or get an industrial electrical book about motors and starters. I had to do this years ago after having trouble getting electricians that were knowledgeable about starters.

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