Why is my grinder shocking the hell out of me?

[Natlek]

Thanks guys

The entire grinder seems to be electrified, so I don't know where I would put a multimeter's probes or what I would be testing in this scenario.

It just started shocking me over the last few weeks after a lot of heavy use with no problems before, and getting worse. What's even more strange is that the longer I run it, the stronger the shock is if I touch something metal on the grinder. When I first plug it in, I don't get shocked at all.

Yes the green wire is 14 gauge wire from a heavy-duty extension cord. There is no visible mis-connection in the wires or any visible short. The building has not been modified lately, except that the meters got changed to digital electrical meters.

I suspect the motor is shorted internally and it's spreading through the frame and entire grinder and trying to find somewhere to go or working back through the grounding wire. I was wondering if anyone has had this happen to them before.

Take cable from power out , then set multimeter on beep .......one wire from multimeter on one phase other on frame on motor .There should be no beep sound on all three wire if motor is OK . Funny , week ago my grinder start to shock me .....I check everything an it is all OK .Then I blow with compressed air all I can access and no more electrical shock .........I suppose that was from carbon dust because some day before start that I worked on carbon handle on that grinder ...........

 

[Natlek]

The VFD has three inputs for wires in from the wall, and three outputs for wires out to the motor. The motor has only three connection lugs (220v 3 phase, two hots and a ground, just like my welding machines), they are all connected securely. I don't understand where the fourth wire is supposed to be. Would that just be from the motor frame to the VFD frame?

For GROUND on three phase motor you need a fourth wire ?????????????????At least in my part of the world

 

[Mecha]

For GROUND on three phase motor you need a fourth wire ?????????????????At least in my part of the world

So you're saying I should have been fried already? LOL thanks Natlek.

 

[Stacy E. Apelt - Bladesmith]

The VFD has three inputs for wires in from the wall, and three outputs for wires out to the motor. The motor has only three connection lugs (220v 3 phase, two hots and a ground, just like my welding machines), they are all connected securely. I don't understand where the fourth wire is supposed to be. Would that just be from the motor frame to the VFD frame?

This post concerns me a lot!!!

Can you show a photo of the motor plate? 220V three phase has three hot wires. Any gorund is a fourth wire to the frame, and is not part of the motor curcuit. Single phase 220V has two hot wires and a ground.

The VFD has three hot wires out L1, L2, L3.

 

[Jesse Latham]

Yup. No wonder it's a shocking situation.

 

[Mecha]

This post concerns me a lot!!!

Can you show a photo of the motor plate? 220V three phase has three hot wires. Any gorund is a fourth wire to the frame, and is not part of the motor curcuit. Single phase 220V has two hot wires and a ground.

The VFD has three hot wires out L1, L2, L3.

Aye ya, it looks like the mystery has probably been solved! I'm out of town and can't get a photo today, but it seems I'm missing the fourth wire (ground) to the motor frame.

 

[Lieblad]

Aye ya, it looks like the mystery has probably been solved! I'm out of town and can't get a photo today, but it seems I'm missing the fourth wire (ground) to the motor frame.

Right, and it also seems you have one of the motors phase wires connected to ground.
Get that part fixed first, then connect a ground wire your motorframe to VFD.

 

[Mecha]

Right, and it also seems you have one of the motors phase wires connected to ground.
Get that part fixed first, then connect a ground wire your motorframe to VFD.

The L1, L2, and L3 of the VFD are connected to the three power inputs of the motor for sure, but just those three.

 

[Mecha]

Told ya it wasn't static electricity. At least I had that part right.

Hopefully this thread helps keep others from making the same mistakes.

 

[Natlek]

Aye ya, it looks like the mystery has probably been solved! I'm out of town and can't get a photo today, but it seems I'm missing the fourth wire (ground) to the motor frame.

That fourth wire /ground/ is for safety only .........three phase motor will work perfectly without ground wire connected .Do you have electrical grounding instalation in your shop or home where grinder is connected ?
https://www.quora.com/What-are-the-differences-between-live-earth-and-neutral-wire

 

[Mecha]

That fourth wire /ground/ is for safety only .........three phase motor will work perfectly without ground wire connected .Do you have electrical grounding instalation in your shop or home where grinder is connected ?
https://www.quora.com/What-are-the-differences-between-live-earth-and-neutral-wire

The circuits in the building have ground wires.

What I'm gathering here is that I have failed to connect the ground wire from the motor frame to the VFD, and because the motor does have some sort of short that's energizing the grinder, it's shocking me because the safety ground isn't attached.

 

[Drew Riley]

I could be wrong, but it sounds like Mecha is just mis-identifying the wires that are connected, but the wires (minus the lack of ground), are probably in their proper places. What he's calling 2 hots and a ground off of the motor are likely just the 3 hots (U,V,W, or L1, L2, L3).

I still would like to see a picture of the motor nameplate, motor wiring, and the wiring into the VFD, just to see if there's anything to be seen, but the fact that Mecha claims it worked just fine for a while is leading me to believe that it's wired (mostly) correctly, and the motor just suffered a breakdown of insulation somewhere that's arcing into the motor case.

 

[Drew Riley]

The circuits in the building have ground wires.

What I'm gathering here is that I have failed to connect the ground wire from the motor frame to the VFD, and because the motor does have some sort of short that's energizing the grinder, it's shocking me because the safety ground isn't attached.

Correct. Again, lack of ground isn't what's causing the short, but it will be what's causing you to get shocked. Electricity always takes the path of least resistance. Our bodies typically have significantly more resistance than a properly integrated ground wire.

 

[Mecha]

Knife to a gunfight is correct. Thanks so much for putting up with with this thread, everyone. It seems my major malfunction was mostly due to not understanding the difference between 1-phase and 3-phase power. Three-phase is something I haven't really messed with before.