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Old 04-01-2013, 01:39 PM   #1
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Old electric motor tripping GFI breaker


I have an older jointer that I've restored. Prior to restoring it I plugged the motor in and started it to verify it worked and it did (that was NOT on a GFI protected circuit). After the restore, I wired the motor back up and plugged it into a GFI protected circuit to test it. As soon as I plugged it in, with the switch OFF, the GFI breaker tripped. I have not tried to plug it into a non GFI protected circuit. I plan on rewiring it soon and wanted to know if there is anything I should be looking out for? Perhaps there's a logical, harmless reason why the GFI is tripping? The hot goes to a switch and goes from there to two wires coming out of the motor. The neutral goes straight to the other two wires coming out of the motor. The ground is simply on a motor housing screw.

Is there a way to verify which of the wires coming out of the motor housing should be connected to the hot and which should be connected to the neutral? They are not identified or marked in any way so I took a lot of pictures before disconnecting them but I'm afraid I might have it flipped.

Note that this is not the electric motor I made a topic about recently (in case you read that one). That was for a table saw I restored and it's working just fine.

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Last edited by BrandonD; 04-01-2013 at 01:43 PM.
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Old 04-01-2013, 03:22 PM   #2
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Old electric motor tripping GFI breaker


If it trips with the switch off then you must have a short between the hot and ground before the switch or some leakage within the switch to ground. GFCIs trip when there is a difference in current between the hot and neutral. There must be some current flowing somewhere to trip it.
Recheck all your connections. Make sure and cable clamps are not too tight causing a short. If you have a ohmmeter you can check for resistance between the prongs of the plug. With the switch off all connection should show open circuit. With the switch on you will get a connection between hot and neutral through the motor windings.

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Old 04-01-2013, 06:01 PM   #3
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Old electric motor tripping GFI breaker


Are you sure the wire going through the switch is the hot, not the neutral? If the hot and neutral are backwards (neutral switched) and the motor has a ground fault, then the GFCI would trip with the switch off. If the hot is switched (proper configuration) and the GFCI trips with the switch off, then the fault is in the cord or the switch area. My money is on the motor having a fault, which is very common for an old motor, and the switch being on the wrong conductor.
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Old 04-01-2013, 10:14 PM   #4
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Old electric motor tripping GFI breaker


Thanks joed and mpoulton. I had some time to go out there and tinker tonight but wanted to get additional advice before proceeding. I tried using my multimeter on ohms to measure resistance on the plug prongs. I tried measuring every variation I could think of with both the switch on and off and it the meter did not seem to even register a circuit as it read 0L the entire time. I know it worked because if I touched the leads together or to me it would register.

I thought I would bypass the switch all together but noticed the switch was a bit complicated to be just a simple switch. It looks like it has some sort of relay? Either way I wasn't sure that plugging the motor directly in would be safe for me or it as it had this contraption wired to it. The faceplate has "Cutler Hammer Motor Control" on it and is pictured below. The hot going to the motor was attached to the bottom left terminal and the hot coming from the plug was attached to the bottom middle terminal.

What should be my next steps going forward? Thanks!

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Old 04-02-2013, 12:50 AM   #5
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Old electric motor tripping GFI breaker


That switch contains the overload protector for the motor. It is single pole, meaning that it switches only one leg of the power. Perfectly normal.

If the GFI tripped when the machine was first plugged in, before the switch was turned on, then there is a ground fault in the cord or the switch. Since you couldn't read anything with a basic multimeter, it is a high-impedance ground fault. Moisture will cause such a fault.

The motor doesn't care which wire is hot and which is neutral. Make sure the ground pin on the plug is actually the one that's connected to the motor frame.

If the GFI trips with only the cord and switch in the circuit, my first suspect is the cord. If it's old and has ever been wet, very often the moisture that cannot get out will trip a GFI.

Rob
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Old 04-02-2013, 09:05 AM   #6
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Old electric motor tripping GFI breaker


I will verify the wiring tonight. If everything seems in check I will replace the wire. Working space is tight unfortunately. It is a single length of 14-2 NM. The insulation is simply stripped near the end of the cord where it enters the switch box. The hot is cut to attach to the switch while the ground and neutral simply pass through to the motor. Extremely cramped with the switch in the box so I doubt there's room for me to make a single let alone two wire nut connections in there. So I will replace it with a single length of 14-2 UF I have on hand in the same fashion. Not looking forward to that... I'll have to pull the motor to reach the electric box... that thing weighs a ton!

If after replacing the cord and double checking the wiring, it still flips with the switch off, can I remove the switch from the circuit and plug the motor directly in to continue troubleshooting, or is that unsafe for me or the motor?

Last edited by BrandonD; 04-02-2013 at 09:09 AM.
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Old 04-02-2013, 09:25 AM   #7
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Old electric motor tripping GFI breaker


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Originally Posted by BrandonD View Post
I will verify the wiring tonight. If everything seems in check I will replace the wire. Working space is tight unfortunately. It is a single length of 14-2 NM. The insulation is simply stripped near the end of the cord where it enters the switch box. The hot is cut to attach to the switch while the ground and neutral simply pass through to the motor. Extremely cramped with the switch in the box so I doubt there's room for me to make a single let alone two wire nut connections in there. So I will replace it with a single length of 14-2 UF I have on hand in the same fashion. Not looking forward to that... I'll have to pull the motor to reach the electric box... that thing weighs a ton!

If after replacing the cord and double checking the wiring, it still flips with the switch off, can I remove the switch from the circuit and plug the motor directly in to continue troubleshooting, or is that unsafe for me or the motor?
I would NOT direct wire this. Take your ohmmeter and go from one plug prong to the other. OL. Close the switch:____, now go from one prong to the motor body:______, and the other prong to the body:_____. Now open the switch and go from the prongs to the body:____, and______. Now between the body and the neutral:_____
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Old 04-02-2013, 05:47 PM   #8
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Old electric motor tripping GFI breaker


It read 0L for every measurement but the last. I cannot get to the neutral without pulling the motor which I'm about to do. Thought I'd give you the measurements I could get now in case that shines some light now.
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Old 04-02-2013, 05:54 PM   #9
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Old electric motor tripping GFI breaker


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It read 0L for every measurement but the last. I cannot get to the neutral without pulling the motor which I'm about to do. Thought I'd give you the measurements I could get now in case that shines some light now.
If you are getting OL everywhere then I don't think your meter is reading correctly and or the windings are grounded and floating. Take the motor leads off your switch and read them directly. Should be near zero.
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Old 04-02-2013, 06:34 PM   #10
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Old electric motor tripping GFI breaker


Got the motor off. 4 wires come out of it in two pairs (connected with two nuts and bolts with the leads from the switch sandwiched between).

Reading resistance between pairs ranges from 0 to 2.0. I will replace the wire now and see if I get some measurements.
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Old 04-02-2013, 08:22 PM   #11
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Old electric motor tripping GFI breaker


Wired in the new cable and tested resistance at each step. Once I got to the plug I measured across the prongs with the switch off and on and got the expected readings. (0L and close to 0 respectively). Hoped for the best as I plugged it in. Breaker didn't flip. Hoped even more for the best and flipped the switch and the motor started up!

Still not entirely sure what was wrong. The wiring seemed sound as I disconnected the old cable and I did the new one exactly like the old.

As usual thanks everyone for your troubleshooting tips. I know just enough to get me (or someone else) hurt and I'm appreciative that I have this forum for people to tell me how I'm being an idiot!
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Old 04-02-2013, 08:24 PM   #12
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Old electric motor tripping GFI breaker


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Originally Posted by BrandonD View Post
Wired in the new cable and tested resistance at each step. Once I got to the plug I measured across the prongs with the switch off and on and got the expected readings. (0L and close to 0 respectively). Hoped for the best as I plugged it in. Breaker didn't flip. Hoped even more for the best and flipped the switch and the motor started up!

Still not entirely sure what was wrong. The wiring seemed sound as I disconnected the old cable and I did the new one exactly like the old.

As usual thanks everyone for your troubleshooting tips. I know just enough to get me (or someone else) hurt and I'm appreciative that I have this forum for people to tell me how I'm being an idiot!
Just had a winding shorting to ground. Glad you got success!
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Old 04-02-2013, 10:09 PM   #13
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Old electric motor tripping GFI breaker


Quote:
Originally Posted by BrandonD View Post
I have an older jointer that I've restored. Prior to restoring it I plugged the motor in and started it to verify it worked and it did (that was NOT on a GFI protected circuit). After the restore, I wired the motor back up and plugged it into a GFI protected circuit to test it. As soon as I plugged it in, with the switch OFF, the GFI Perhaps there's a logical, harmless reason why the GFI is tripping?
It is not unusual for there to be some leakage to ground in some
of the older style motors.
Its not really a fault, is just the way they were.
Currrants were induced into the frame from
the feild windings.
And in the older days the ground would bleed off the
small leakage currant.
Because they did not have GFCI;s then it was not a problem.

How ever now days with wide spread use of GFCI's
it means that they are no longer compatable with
the modern distribution system.

Unless you can find a way to avoid using the GFCI,
but I dont know if code would permit this !
Depends on what area your in !
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Old 04-03-2013, 01:02 AM   #14
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Old electric motor tripping GFI breaker


Guys, perhaps a lesson in basic troubleshooting is in order here;

1) Cord is plugged into GFI outlet, motor switch is off. GFI trips.

2) Cord is replaced. All is good now.

The only possible problem is that the original cord was bad. The motor was and still is, ok.

Rob

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