Single to 3ph bandsaw giving a small shock occasionally Any idea the cause?

As the title states my bandsaw is shocking me every once in awhile and I cannot figure out what the cause is. It seems to do it where the powdercoat has worn off and if I’m wearing nitrile gloves as I do most the time i never notice it. I checked grounding and everything is tight and looks correct. The only thing I can come up with is if one of my motor wires is wired out of phase? Perhaps that thought is incorrect? I’m not an electrician but I’m also not new to wiring and have formal training in low voltage electronics. The other thought is I am building up a static charge somehow and that is what I am feeling. It isn’t intense like 110v or 220v. In fact when I get the shock it feels like a sharp static shock that hits up the forearm a little and makes me pull my hand away as you would a door knob after walking across carpet except I don’t hear the static crack as you typically would instead I feel more of a pulse algorithmic charge like you’d get from the wall socket. Lol, sounds like I have experience being shocked, I’m sure we all have been there once or twice before. The vfd is 220v single phase to 3 phase 3/4 horsepower techtop motor on a 5” bandsaw. I’d like to not worry about getting a bigger shock or any for that matter and fix the issue even if it is some type of static build up finding a way to eliminate it would be great. As I stated the grounding is solid to the vfd and motor and from the vfd to the saw chassis where it is mounted and it is also grounded through the motor housing to motor mounting plate as it is currently wired. So I don’t know what else it could be except a wire out of phase possibly back feeding through the ground giving an alternator like effect. Thanks ahead for any input.

Is the ground rod dry? pour some water on it so the soil is damp. I suspect there is a problem with the ground floating. Somewhere the ground path is broken. Use an ohm meter and measure resistance from the machines unpainted metal to a good ground like a metal water pipe.
Bill D.

There are two basic possibilities.

This could be a static charge buildup. Bandsaws as a class are prone to this kind of problem, especially if they have rubber tires on the wheels. If this is the cause, then you can probably deal with it by mounting a piece of metal tinsel or flat braid to the body so that it lightly rides on the tire.

This could also indicate a more serious problem in your wiring. Every machine must have an equipment grounding conductor (green wire) bonded to it. And the EGC (green wire) and neutral (white wire) are not allowed to be connected anywhere except your supply panel. If you have black/white/green coming in to your VFD, you may need to extend the green so it is also connected to the frame of your saw. Or you may have a dodgy neutral between your panel and your saw. You say you've got good grounding, but it's worth checking again, as this is a classic cause.

One other possibility is that you have leakage from the input or bus stages of the VFD to your saw's frame.

Get an extension cord and plug into nearby outlet.

This is now your reference.

Measure voltage at cord to confirm good then measure from cord safetyground to every shiny spot on band saw.

With off, running and cutting.

Any measured voltage indicates not grounded item that may be hot.

All metal parts need to be bonded to single ground.


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Mystery solved. Duplicating the problem I come to realize only occurs if I touch my mill at the same time as I touch the bandsaw so you are correct it’s a bad wiring issue. There is 55v between the bandsaw and the mill so I have a polarity issue going on. That 55v makes sense now it isn’t enough to floor me but I didn’t like getting the damn shock. The two machines are grounded the same to the wall so I suspect it is coming from the wiring between the vfd and motor and I need to change a leg. I will take it apart this weekend and get it fixed. Looking back I did replace the vfd approx 3 months ago and must’ve inadvertently tied one of the wires incorrectly. I appreciate the input reading all the suggestions I pulled out the meter and after I couldn’t find anything directly on the bandsaw came to the conclusion it must be a polarity issue. Sure enough. Many years ago when we had two prongs no ground on those old pinball machines an arcade I was at had two machines next to each other with reverse polarity. Those mothers would floor you if you managed to come in contact with both at the same time.

Sounds like you may have an open neutral or ground at or after the VFD or neutral and one hot switched. What meter did you use as most read incorrectly on a VFD's output. 55V with low load on VFD may be as high as twice supply voltage but with very short duration i.e. 55V RMS by meter but actually 220V with a 25% duty factor.

you have a hot wire touching chassis

wippin' boy said:

you have a hot wire touching chassis

Click to expand...

This!

The way I found out my ground path in my shop had an issue was when I pinched a hot wire in a box cover and got a tickle every time I touched the conduit in my shop. A little investigation found the pinched hot-wire and the broken ground path. Problem solved.

I would say you have a similar problem. Your most critical IMHO, is the faulty ground path. Find the fault. With a good ground path a hot-wire touching the chassis should (in theory) trip the breaker. The secondary problem is the hot-wire touching the chassis. Fixing only that problem doesn't make the machine safe, it only fixes one of the issues.