Old cap start motor trips GFCI (safety question)

[Shiftless]

Technical question...

I have a vintage 1951 Craftsman half horse motor powering my Craftsman 100 drill press.
It runs fine when plugged into a non GFCI protected receptacle, but trips when using a GFCI circuit after running about 30 seconds with no load. If I bypass the ground connection by using the little gray 3 prong into 2 adapter, it runs fine on the GFCI circuit.

Is it safer to...
A:
run a separate non-code compliant circuit (no GFCI) dedicated for the drill press just so I can run a ground wire.

Or
B:
Use the 3 into 2 adapter on the existing circuit and rely on the GFCI to prevent shocks by its monitoring the balance between hot and neutral.

I suppose another option would be to replace the 67 year old motor with a new one that plays nicely with GFCI.

BTW, if anybody is looking closely at the pic of the motor, yes, I have the 4 pieces of threaded rod and cap nuts that belong there. I removed them for painting. I also removed the cord.

 

[Hdonly0]

I am not a professional electrician so I can say this. I would run it on a regular receptacle with ground and make sure the motor ground is connected. Done, drill some holes. That's just what I would do. Only you can decide what you do.

 

[u3b3rg33k]

sounds to me like you have a legitimate ground fault if removing the ground stops the GFCI from tripping - the first place i'd look would be the motor's junction box.

 

[Lassen Forge]

It sounds like you're leaking current to the motor case once the motor gets warm... not uncommon on a 75 year old motor, considering the age of the insulation, etc. Does it trip faster when you have it under load? If so it sounds like the (original) insulation is breaking down somewhere on your fields, allowing current to migrate.

If you want to be 110% safety minded, you could spend the $$, take the motor to a local motor shop, have it checked, windings rewound, etc... won't be cheap, but then you have essentially new guts in a vintage motor housing that should last another 75 + years. This is the route I would take.

Otherwise - as long as your grounds are good, and you know the motor is grounded, you could put it on a non-GFI circuit and run it like your granddad did pre-GFI, just remembering you no longer have one layer of safety that you would with modern gear. Also remember as the motor gets older, those 75 year old electrical components will be getting older, and more prone to malfunction.

Getting a replacement motor probably won't cost as much as the rewind and rebuild, but to me that's like throwing in the towel. If you have the luxury of time, and you appreciate vintage gear (that looks vintage), well, keep your local motor shop in business!

 

[Shiftless]

Thanks for you input guys.

I do have the luxury of time and I certainly do appreciate old machinery.

The reason I don’t think it’s a true ground fault is that it always runs for a while before tripping the GFCI. If there was an internal short to ground, wouldn’t that trip right away? It delayed trip several times, right around 30 seconds of run time. (Estimated...I didn’t break out my stopwatch for this yet)

I opened up the motor junction box to inspect wiring and replace the old cord. It had been replaced before, but I am going with a new molded plug replacement cord assembly. Of course the original wires had somewhat brittle insulation and there was some old electrical tape, but I will put the new cord on and new electrical tape to shield wire from the motor housing. Tape and/ or “liquid electrical tape goo” for extra wire insulation where it touches the housing.

 

[Negen]

Does your gfci also have arc fault built in to it ?I had this issue after a remodel in o e of my rental properties and the electricians installed dual arc/ground fault outlets and the garbage disposal wouldn't work called the local code inspector and was told kitchens only bedded ground faults so had them change the outlets for me. Could be worth looking into.

Another thing that seemed to help is if the wires are screwed onto the outlet wrapping that with the heavy duty rubber based electrical tape seemed to resolve some issues I had with motors running at full speed instantly . sometimes running high amp motors that when turned on didn't slowly ramp up sometimes a small spark would occur tape seemed to stop this also only used tape that is the heavy duty rubber stuff as normal electrical tape seemed to get dry when aged.

I had most my issues with 2000 watt 220 inverters or motors.

Sent from my G8141 using The Garage Journal mobile app

 

[Shiftless]

Negen:
Thanks for sharing your experience.

What’s “kitchens only bedded ground fault”? Was that a typo? I assume you meant to type NEEDED

No arc fault protection. Non GFCI 20 amp breaker.
I have a high quality 20 amp GFCI receptacle first in line from the sub panel. All the garage wiring (solid 12 ga) is 2 years new. EMT with separate green ground wire inside. One duplex receptacle per 4x4 box. Receptacles are industrial quality with wires entering the back and tightened with screw down clamp.

 

[Lassen Forge]

The reason I don’t think it’s a true ground fault is that it always runs for a while before tripping the GFCI. If there was an internal short to ground, wouldn’t that trip right away? It delayed trip several times, right around 30 seconds of run time. (Estimated...I didn’t break out my stopwatch for this yet)

That's what's making me think it's the internal windings in the motor leaking current to the shell of the motor and creating a fault - When it's cold, it's fine, but as the motor warms up the ancient insulation starts to break down and allows a small current to pass and triggers the GFI. Once it cools back off, the insulation goes back to its original state, and you're fine - until the motor warms up again.

It's not a direct short (as in Arcen, Sparken, and Fizzpoppen), it's current leakage. GFI's are notoriously sensitive to this.

 

[wyliesdiesels]

Technical question...

I have a vintage 1951 Craftsman half horse motor powering my Craftsman 100 drill press.
It runs fine when plugged into a non GFCI protected receptacle, but trips when using a GFCI circuit after running about 30 seconds with no load. If I bypass the ground connection by using the little gray 3 prong into 2 adapter, it runs fine on the GFCI circuit.

Is it safer to...
A:
run a separate non-code compliant circuit (no GFCI) dedicated for the drill press just so I can run a ground wire.

Or
B:
Use the 3 into 2 adapter on the existing circuit and rely on the GFCI to prevent shocks by its monitoring the balance between hot and neutral.

I suppose another option would be to replace the 67 year old motor with a new one that plays nicely with GFCI.

BTW, if anybody is looking closely at the pic of the motor, yes, I have the 4 pieces of threaded rod and cap nuts that belong there. I removed them for painting. I also removed the cord.

This only adds more non code compliant and unsafe things to the mix.

If the GFCI is tripping, its trying to tell you that there is an issue.

If you use that adapter and the frame is on concrete all you will have done is redirect the fault current...

Why not get the motor checked out?

Safety first

Thanks for you input guys.

I do have the luxury of time and I certainly do appreciate old machinery.

The reason I don’t think it’s a true ground fault is that it always runs for a while before tripping the GFCI. If there was an internal short to ground, wouldn’t that trip right away? It delayed trip several times, right around 30 seconds of run time. (Estimated...I didn’t break out my stopwatch for this yet)

I opened up the motor junction box to inspect wiring and replace the old cord. It had been replaced before, but I am going with a new molded plug replacement cord assembly. Of course the original wires had somewhat brittle insulation and there was some old electrical tape, but I will put the new cord on and new electrical tape to shield wire from the motor housing. Tape and/ or “liquid electrical tape goo” for extra wire insulation where it touches the housing.

Depends on the fault current and resistance...

 

[Shiftless]

Thanks guys. I’ll install the new cord and see if my motor will run OK on the GFCI circuit with the ground wire attached and the old wires better protected from rubbing against the frame.

 

[Shiftless]

UPDATE

New cord and plug installed. 14ga. Southwire SJOOW
Rubber grommet where it enters the housing. Strain relief inside.
Extra rubber based electrical tape between old wires and the motor frame.
Same kind of tape around the spliced neutral wire and the exposed terminals of the switch. The metal housing of the big flat rectangular capacitor was very close to the switch terminals. Seems to me that the cap should have a paper cover, but no remnants were found.

Runs great now! No problems with leakage to ground at least for now. (Knocking on wood)
I bench tested it and let it run for 5 minutes.

Next step is to reassemble my drill press!

Thanks again guys for your guidance.