Another need help with a reversing switch. SBL GE motor

I am new to this forum and there seems to be a lot of knowledge.

I have a single phase 110 volt motor. It is on an Old South Bend lathe. Someone twisted the wires together and ran it that way. In the reversing switch they cut wires so it only ran in forward. I picked up a new reversing switch and I found a problem. It does not work right. I can follow a wiring diagram and am quite good with electricity. I am thinking maybe a motor problem, that is why it was hacked previously. 3 of the 4 wires are still marked. So that helps. And they seem to match the pairs for the windings.

OK.... The motor is 110 volt, single phase, 4 wire, Guessing capacitor start because it has a capacitor hump.... It was designed as reversible (4 wire) 2 wires to one leg... the other 2 wires to the other leg. Runs fine. You are supposed to reverse one winding, either winding, and it should throw the motor in reverse. I reverse the wires and once I got a hum with no rotation and the other times tripped 20 amp breaker instantly. Trying different combinations. There is only one combination that works and that is in forward. The original way it was hooked up when I got it.

I made sure the 2 windings were isolated. They are isolated from the other winding, and both are isolated from the chassis (ground). Both windings are approx .6 ohms. The only thing I can come up with is MAYBE a bad capacitor????

Scratching my head on this. Any ideas??? I could understand a shorted winding... But why does it run forward fine??

Figure 3 should be close to what I have. It is a 3 pole, double throw switch. Ran horizontally in the picture.



This picture is a type KG motor... I think mine is a KC. But I can't find any internal wiring for it. I am not sure where the relay should be even if there is one still there. Being almost 80 years old, who knows how many hands it has gone through.


Any ideas where to go next?

The 4 wire setup you show makes no sense as-is. There WERE instant-reverse single phase motors, and that diagram may be a somewhat corrupted version of that.

Something does not sound right. For a normal motor, the start winding works either way, if it works one way it pretty much has to work the other.

Normal motors just have the two windings, the capacitor is in series with the start winding and the centrifugal switch. The start winding is connected until that switch opens at maybe 60 or 70% speed. They just work, They also just work when used with a revrsing switch, although they do NOT do instant reverse, you have to let them slow down.

Your motor, if it is a different from usual type that has a relay, etc, may not work the same way. It has been a while since I looked at the instant reverse single phase motor setup, but I do not think it will in any way work with a regular reversing switch. It has the same basic parts, but you would need to disconnect the special relay setup if there is one.

For normal motors, often the red and black are the start winding, I think GE used that standard wiring color code

So..... is there a capacitor under that bump? ..For a cap start motor, the windings can be close in resistance, for a resistance start motor the start winding is considerably higher.

Show a pic of the motor data plate, and one of the wiring box and wiring...... Also look on the inside of the wiring box cover, there often is a wiring diagram there.

I'm wondering if a single phase motor with start and run Cap. and connection to the Caps were reversed. Would the run Cap that's not connected to the centrifugal switch be enough to slow the motor so that the switch will close adding the start Cap.??

JST said:

The 4 wire setup you show makes no sense as-is. There WERE instant-reverse single phase motors, and that diagram may be a somewhat corrupted version of that.

Answers interlaced... That is the original diagram for the SBL GE motor from South Bend lathe. Now the last picture showing the relay I got off the net. I am not 100% sure of it.

Something does not sound right. For a normal motor, the start winding works either way, if it works one way it pretty much has to work the other.

I completely agree. I can't figure out why it won't

Normal motors just have the two windings, the capacitor is in series with the start winding and the centrifugal switch. The start winding is connected until that switch opens at maybe 60 or 70% speed. They just work, They also just work when used with a revrsing switch, although they do NOT do instant reverse, you have to let them slow down.

Not sure about the instant reverse myself. Kind of spooked me to do that to a machine. I was starting it in reverse after it stopped.

Your motor, if it is a different from usual type that has a relay, etc, may not work the same way. It has been a while since I looked at the instant reverse single phase motor setup, but I do not think it will in any way work with a regular reversing switch. It has the same basic parts, but you would need to disconnect the special relay setup if there is one.

For normal motors, often the red and black are the start winding, I think GE used that standard wiring color code

This is an OLD GE motor form the 40s I am guessing. No colored wires. They have metal crimps on the wires as tag numbers

So..... is there a capacitor under that bump? ..For a cap start motor, the windings can be close in resistance, for a resistance start motor the start winding is considerably higher.

I will run out in a few and check what is underneath it. I hope it has a size on it. Almost 80 years old it may be time for a replacement.

Show a pic of the motor data plate, and one of the wiring box and wiring...... Also look on the inside of the wiring box cover, there often is a wiring diagram there.

This thing is so old there is no wiring cover. The wires stick out the side of the motor itself. It runs good forward, so I am trying to hook it up correctly for forward and reverse.

Click to expand...

Thanks for your help!!!

Froneck said:

I'm wondering if a single phase motor with start and run Cap. and connection to the Caps were reversed. Would the run Cap that's not connected to the centrifugal switch be enough to slow the motor so that the switch will close adding the start Cap.??

Click to expand...

From what I know AC starting capacitors they do not have a polarity. So the leads should not make a difference.

JST said:

Something does not sound right. For a normal motor, the start winding works either way, if it works one way it pretty much has to work the other.

For normal motors, often the red and black are the start winding, I think GE used that standard wiring color code

Show a pic of the motor data plate, and one of the wiring box and wiring...... Also look on the inside of the wiring box cover, there often is a wiring diagram there.

Click to expand...

Well if all else fails start over and regroup... To get a good look at the motor I have to crawl all the way under the lathe. Just my luck... Why do people do this to the tags????


OK so all the way in the back is the wiring cover... Hmm it is not where the wires come out of the motor. Of course no wiring diagram anywhere. The cover is completely blank.... Hmm you did say red and black wires for the start winding??? In person you can see red on the bottom wire.


Well since the 2 windings had the same resistance, I wonder if they are a series/parallel windings for 110/220 and when I reversed one winding it through one 180 out of phase. That sure as heck would throw a wrench in the works!!!

Oh and the cover had a starter cap in it. It looked very old but in good shape. No relays at all.

Now for some rewiring.

Brian Ski said:

From what I know AC starting capacitors they do not have a polarity. So the leads should not make a difference.

Click to expand...

Cap.s used in motors do not have polarity, you are correct! The cap. is used to create phase shift. Changing the connection changes the phase relationship and therefore will change the direction the motor will start. The reason it will not instantly reverse is as mentioned the centrifugal switch must reach the speed at the point it will close and reconnecting the capacitor. A run Cap is connected before the switch so it's in the start/run winding at all times. My question was will reversing the connection to the start/run winding and therefore providing a breaking force slowing the motor so that the centrifugal will will close and add the start Cap. reversing the motor. Saying that. will a Cap. start/run rotate or brake rotation if power is applied to the start/winding only if the connection reverses the phase? Might explain how a relay is used to provide instant reversal.

Froneck said:

Cap.s used in motors do not have polarity, you are correct! The cap. is used to create phase shift. Changing the connection changes the phase relationship and therefore will change the direction the motor will start. The reason it will not instantly reverse is as mentioned the centrifugal switch must reach the speed at the point it will close and reconnecting the capacitor. A run Cap is connected before the switch so it's in the start/run winding at all times. My question was will reversing the connection to the start/run winding and therefore providing a breaking force slowing the motor so that the centrifugal will will close and add the start Cap. reversing the motor. Saying that. will a Cap. start/run rotate or brake rotation if power is applied to the start/winding only if the connection reverses the phase? Might explain how a relay is used to provide instant reversal.

Click to expand...

Long day... I will have to ponder that... BTW the capacitor looked in good shape and the leads were soldered to it. So reversing it would take a bit of work.

In the mean time... I have not tried my new idea yet. I needed a new piece of 14-2. I had to settle for 14-3. (the connector did not have a lot of room. Maybe with time tomorrow.

BTW since you know more than I do about this. I found this about the reversing motor. I don't think it is my motor, but interesting. As far as I can tell, I don't think mine has a relay. It does look like several hands have been in it.

Normally, the motor, if switch is set to reverse position when running, wiould not do anything different, because the start winding is not connected. Shorting the centrifugal switch, and connecting the winding in reverse direction, WOULD provide a slowing force, which would slow the motor, and end up starting it in the other direction, yes. The short to the centrifugal switch would have to be opened. That is a big load on the start circuit and capacitor, but it would work.

Your actual motor appears to be a standard single phase single voltage motor. It should just work, if it works one way, it should work the other.

But, I am slightly puzzled by the wiring I see. I assume the green ground wire is actually being used as a power conductor (a no-no, but never mind that for the moment). If so, then I assume that 2 conductors are being used for the run winding, and two for the start.

As far as the motor is concerned, it just needs the two wires that have terminals interchanged on the studs, which is where the power comes in. Doing that should reverse it. (after a stop)

So, as a tiebreaker, I would hook up normal 2 wire power to the studs, without the switch, observe the motor run one way, then reverse those wires with terminals, and see if the motor then starts in reverse.

Then, if that works both ways, you know that your wiring to the reversing switch is NOT what you think it is. There ARE more than one style of reversing switch, and they wire up differently.

If interchanging the terminals does NOT reverse the motor, then there is another issue, and frankly, I have no good ideas what it might be, other than a shorted wire inside the motor.

One point worth mentioning.... Single phase 110/120 V wiring has a hot and neutral. The neutral works fine if hooked to the GROUND, even though that is not actually allowed. But the motor would run and not pop a breaker (other than a GFCI).

But, if you were to REVERSE the connections, that motor wire that used to be the neutral would be the hot, and if the hot is shorted to ground, it will pop the breaker. So it is worth checking to see if any of the wires are in any way connected to the case of the motor (which I assume has a ground wire either directly or through the machine structure).

JST said:

But, I am slightly puzzled by the wiring I see. I assume the green ground wire is actually being used as a power conductor (a no-no, but never mind that for the moment). If so, then I assume that 2 conductors are being used for the run winding, and two for the start.

As far as the motor is concerned, it just needs the two wires that have terminals interchanged on the studs, which is where the power comes in. Doing that should reverse it. (after a stop)


One point worth mentioning.... Single phase 110/120 V wiring has a hot and neutral. The neutral works fine if hooked to the GROUND, even though that is not actually allowed. But the motor would run and not pop a breaker (other than a GFCI).

But, if you were to REVERSE the connections, that motor wire that used to be the neutral would be the hot, and if the hot is shorted to ground, it will pop the breaker. So it is worth checking to see if any of the wires are in any way connected to the case of the motor (which I assume has a ground wire either directly or through the machine structure).

Click to expand...

I follow what you say... 1st the green wire... I understand electrical work, except for a bit of this... I was not a fan of using green for power. Except I could not find a 5 wire (or 4 wire without a green at lowes.) Not very common wire.

Yes, it was the 2 terminals on the studs to reverse the motor.

I follow on the reversing power if shorted. I ohmed out all the windings and everything was isolated from the ground.

Thanks for the ideas.

Heads up for anyone following this thread. On the old South Bend Lathe wiring for a reverse switch. The wires labeled 1-4 on the front of the motor are for 110 if wired in parallel and 220 if wired in series. But they must be in correct order. Not sure right now what the order is since I didn't mess with that.

To reverse the motor you have to reverse the 2 wires under the small cover. You can use a reversing switch. There are several reversing barrel switches, they all should work, BUT They are not all wired the same.

Thanks for the help guys... Now onto learning how to use a lathe.