Wireless

A customer of mine has a industrial meat grinder, whenever you touch the case of the grinder and the walk-in you get a shock. The voltage between the cases is 37v. All the grounds in the grinder seem to be ok. Aside from the motor what else can be the culprit?

Cerrak

Maybe a poor ground someplace on or in the walk in?

Had a similar problem in a residential. touch fridge and built in oven at same time and you could light up a neon bulb.

You could light up a 100 watt bulb between the dryer and cold water pipe.

turned out the grounds became disconnected in the service panel.

Rong

One things I would do is to prove which one is causing the problem. I suspect the walk-in. Maybe the defrost strip around the door or vent is shorting out? Or does the cooler even have those? Could be the fan motor on the chiller inside .Just a couple of things I have seen in the past.

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Wireless

sorry I should have mentioned I tested both to ground, it is the grinder.

JohnJ0906

There has to be A) a problem with the meat grinder EGC, and B) a high resistance short in the machine somewhere.

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All responses based on the '08 NEC
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Billy_Bob

I've seen this happen a LOT with electric motors. You have all sorts of un-insulated conductors inside the motor, many times a built-in fan for cooling the motor, then this all surrounded by a metal case.

Then the fan sucks in all kinds of crud. Add years of oil and crud and you eventually get a fault to the metal case.

win

Check the nutral as it sounds like it is going to earth and until it reaches about 50 volts it will not blow the fuse
Win

Wireless

One of the phases in the motor was bad.

gilbequick

What was bad about it?

Raverill

Are the meat grinder and the walk-in box fed from the same source? Both units can be properly grounded to their source. However, if the sources of the grounding are not properly bonded to each other, there can be a difference in potential, in this case, 37 volts. The reason all grounds must be connected to each oher,(bonded), is not only to create a low impedence path for fault, but to create a "zero potential" situation between grounded metal cabinets, machinery, etc. This is especially important around swimming pools and spas, and cattle feeding/watering equipment. That is why the NEC requires ALL metal equipment, electric or otherwise, around a swmming pool or spa to be bonded to each other. It is also why all equipment grounds operating under the same main, MUST be bonded to each other.
Another source of the problem could be that an unqualified person has used the neutral bus in a panel as an equipment ground, or vice versa. This could not only create your phantom 37 volts, it could kill somebody. Many electricians and equipment mechanics think that the grounded neutral conductor and equipment ground are more or less interchangeable. They are not. The NEC is very clear on this.
I hope this helps.

Wireless

Now I am not sure if the motor was bad! I meggered the leads on the motor, one of them came up with little resistance. I brought the motor to a repair shop, they repaired it. I installed the motor, turn on the machine and feel a slight tingle I ignored it till it happened a second time. I took a reading from the casing to ground it was 70 or 90 volts (more then the original 37v). I meggered the leads again everything was fine. By mistake I meggered the line instead of the motor leads, that reading came up no good. I am not sure if I made the same mistake the first time and brought the motor in for nothing or there were two problems.

One of the power leads bypassed the contactor ( it was always hot) after i put it back through the contactor the casing to ground was 152v.

I checked the subpanel the neutral bus is isolated. The subpanel uses the conduit as EGC.

All input is appreciated.

Billy_Bob

What I would do is isolate the motor from the grinder and grinder case from any ground connections.

I understand this might be a "monster machine", but can you say isolate the grinder as it is now from any ground connections? Then test the grinder metal case with power applied?

Then if the problem is with the grinder, might want to remove the electric switch cover plates and peek inside.

Then if you can't see any visible problems, remove the motor to isolate it from its metal case touching or connecting to the metal case of the grinder. Use extention wires/wire nuts to connect the motor to the grinder wiring.

NOW... Just placing an electric motor on the ground and applying power... That motor is going to go flying! So need to fasten it down some way so it stays put. Perhaps a couple of 2 x 4's with the motor on top of these and motor strapped to the 2 x 4's. Just be sure the metal case of the motor is not grounded for this testing.

Anyway now you have the grinder metal case isolated from ground and the motor metal case isolated from the grinder. Apply power to the motor, then check the motor metal case, then the metal case of the grinder, and the ground going to the subpanel.

This should pinpoint the problem.

Billy_Bob

P.S. If the above does not find the problem, might also want to [carefully] test the shaft of the motor while it is running. I would think that if the shaft was leaking to ground on the motor, the leak would be to the case as well, but you never know...

Wireless

I am pretty sure I found it now! the ground wire in the power cord is not continuous.

Billy_Bob

Good work!

Did you find the source of the leak to ground as well?

Wireless

No, it could be anywhere. The elecrical componets have a lot of corrosion, I am going to see if I can replace them.

Billy_Bob

Oh... Sounds like fun!