Electrical peeps, cypher this one for me.

[RaisedByWolves]

The Vevor Ultrasonic cleaner thread brought this to mind.Something was going on in my shop, that is now corrected but I don’t fully understand the issue.

I added an led light to my drill press along with a step down converter to power it.

When doing the work, of course juggling three hand fulls of things with two hands I took the liberty of using two different ground screws inside the junction box cast into the machine.

Essentially one for the cord and a separate one for the motor, and both were there before I started.

Everything seemed fine and worked well, then one day I got a heavy “tingle” from the drill press when my sweaty arm rested on it.

Then a separate time I got the same tingle from the bandsaw that was next to it.

Knowing what work I had done on both machines and went in and checked everything over and everything looked correct.

I was still occasionally getting hit though.

Went back into the drill press and thinking about the separate ground screws, I went in and put both wires on the same screw.

That solved the problem, but I don’t understand what was going on.

In my mind and with my limited electrical knowledge, I had both screws connected via the frame of the machine and this should have been good.

So for future reference, any idea what was going on here?

Never had this before or since.

 

[Reddinr]

The tingle you felt is likely due to leakage current somewhere. Having likely improved the bonding of the metal of the one machine would just conduct the leakage current back to ground instead of through you to ground. Unless something else changed coincidentally, your leakage problem still exists, it is just not going through you. Because you got the tingle from a machine near by, that would hint to me that you have a bad ground that is common to both machines, along with another problem.

Are both machines on concrete or a conductive surface? Plugged into the same set of outlets? What is the voltage of each machine? Is there a neutral wire to each? VFD involved anywhere? Is the LED of good quality (New, rated for any humidity you might have, UL Listed etc.)

Leakage current is always there, it is generally just small. It gets large enough to feel if the insulation to ground becomes poor, there is high frequency involved such as a VFD, filter capacitors to ground etc.

You can use one of these if you want to test the insulation in your machines to find out what is going on. First, disconnect the machine from power, then use something like this:
https://www.amazon.com/Klein-Tools-...d=1735667303&sprefix=megg,aps,200&sr=8-3&th=1

Maybe you could borrow one. It would also be a good idea to double check that the ground wires that go from the machines back to your panel are all solidly connected. Sometimes a loose connection can go away for a while because something shifted, got hotter/colder etc. But it could come back just as easily. If both chassis screws you describe were solidly connected to the wires and to a chassis that had good continuity to the other screw, there is no reason that using two screws would cause your problem. (A few "ifs" there.)

 

[RaisedByWolves]

The tingle you felt is likely due to leakage current somewhere. Having likely improved the bonding of the metal of the one machine would just conduct the leakage current back to ground instead of through you to ground. Unless something else changed coincidentally, your leakage problem still exists, it is just not going through you. Because you got the tingle from a machine near by, that would hint to me that you have a bad ground that is common to both machines, along with another problem.

Are both machines on concrete or a conductive surface? Plugged into the same set of outlets? What is the voltage of each machine? Is there a neutral wire to each? VFD involved anywhere? Is the LED of good quality (New, rated for any humidity you might have, UL Listed etc.)

Leakage current is always there, it is generally just small. It gets large enough to feel if the insulation to ground becomes poor, there is high frequency involved such as a VFD, filter capacitors to ground etc.

You can use one of these if you want to test the insulation in your machines to find out what is going on. First, disconnect the machine from power, then use something like this:
https://www.amazon.com/Klein-Tools-ET600-Megohmmeter-Insulation/dp/B07ZZX5TK8/ref=sr_1_3?crid=36Q02XQBANNFD&dib=eyJ2IjoiMSJ9.GLB_bRhSHC6W7t3Y60T4n1ofsjYvHcD_VOVdWH__SmiO-lIYiAoJvqTegMehPAMlaIAxJw0TpHwxd0pEfYzwUSZw6YrJVZucpnCSrGdx45PPH37Tt0COQF1-2zeUUJKYGRLx03-lim_CTTn_68WkZs-Q2XiQ2mYf_uhyRd8iv6SqKSyw-XKAYa3rHXJzfqcMAzE66FeR8eh-XYJfGVqOu1QYJPVJQEpFajugMU4yvfs.42VE-qm5DYi4wRiydgnZnbp5RQOMB7e3kWlBLqaXnXg&dib_tag=se&keywords=megger&qid=1735667303&sprefix=megg,aps,200&sr=8-3&th=1

Maybe you could borrow one. It would also be a good idea to double check that the ground wires that go from the machines back to your panel are all solidly connected. Sometimes a loose connection can go away for a while because something shifted, got hotter/colder etc. But it could come back just as easily. If both chassis screws you describe were solidly connected to the wires and to a chassis that had good continuity to the other screw, there is no reason that using two screws would cause your problem. (A few "ifs" there.)

No VFD, wood bench and both plugged into the same outlet via a power strip.

I do have a janky fluorescent light setup on this same circuit.

Any way to test the main outlet with a multi meter for issues? I have a multi meter, gfci tester circuit sniffer, but no megger.

Mainly, ok, I have a leak. But it it a hazard? It felt weak like a 9v on your tongue, maybe weaker except it was across my skin.

 

[Jake M]

Agreed, that tingle is leakage current "somewhere". It needn't be a lot if it's got nowhere to go, and it'll elevate the voltage of the machine very easily. More volts and low (nearing no) amps is what gives you tingles. Some volts with a bit more amps feels like a zap, even if it's not enough to burn or truly hurt. The point where the electricity hits you accutely overrides the "tingle" and you'll never notice it.
(That's not safety advice on what's OK to live with, that's more of a way to "estimate" the problem).

Some leakage is normal, but its' very small. VERY small. Like 5 milliamps small. That's (about) where GFCI's trip.

The fact that you didn't have this, THEN it showed up, suggests to me that something changed. There's a new step down converter in there, with two voltages available to it, one of which MAY be isolated from the building power, or they may be partially co-conjoined, as well as a new lamp in there.

Both of those are subject to question for the very sake of their introduction at the time the problem came up.
The fact that it carried to the saw, which is on the same outlet strip (bad plan, but I'm guilty too on occasion....), that strip will "join" each of the two wires from each of the two machines, so they all become one circuit. The ground voltage by necessity was elevated in that outlet strip as well. Possibly the outlet where the strip is plugged in. Possibly further up the system. This tells me that the problem which is (was) providing this voltage WAS connected to the ground, both at the drill press, AND at the band saw, at the time the symptom was active... A bad connection from the separate motor ground inside the drill press could not do that.

Thus, I've come to believe that while I don't know for sure what the problems are, I believe there's more than one issue going on here.



A, You've got (or had) a current leak "somewhere" in that drill press (or the saw, but you only mentioned buggering with the drill....), and whle it should be zero, some truly are acceptable. So it's obvius that either the leak was WAY more than acceptable, or it's got no where to go.
B, that current leak is capable of elevating the voltage ON THE GROUND WIRE, which is what carried it from one machine to another. If the ground wire were working properly, it should be able to carry enough current to open the circuit breaker. It should have nulled that to something you'd never have been able to notice, but there was voltage. This elevated voltage tells me that something's not right with that ground "somewhere", that's upstream (towards the outlet) from the point in the receptacles inside that outlet strip where the two machines are joined.

My advice (for what it can be from this far away), is to investigate that ground system carefully. It'd be better if you could recreate the fault, but I can see the impracticality in that. But the ground needs to dissipate "spare electricity" into the ground.

Questions to ask yourself- Are these grounded as "common" or are these grounded with a separate equipment ground (green wire) ground? How is the outlet set up in that regard? Are the grounds and the common/neutral wire joined there. (Or where'd it come from, are they maybe joined inside the outlet strip? Is there some place in the wiring from that outlet to the service entrance where the neutral and the ground might have got bonded a second time, leaving parallel wires and competing current on that wire which "should" be sitting there and doing nothing but waiting for a problem? Is any part of that circuit grounded by conduit or metal cable, or otherwise using fittings and such, in lieu of the green wire? That is legit, as all of those type of connections WILL clear a fault, but they don't hold up to continuous current, they develop resistance. Anyhow, if youy have those conduit grounds, it's the first place to look for trouble of this nature.

 

[silence dogood]

What you seem to have here is a ground loop. When you had the ground wires on two different screws even though it was in the same box, there was enough resistance to cause a voltage and current flow. That is what Ohm's Law is about. That is also why when you look in a panel, you will notice all the ground wires are connected to one buss bar.
Is your floor concrete? Concrete with a little moisture will conduct a current. It would not hurt to place a rubber mat in front of your machines.
Also, take your meter and put one probe on one machine's ground and the other probe to the other machine's ground. Technically, the readings for both current and voltage should be zero. If it's over 5ma, then make sure the wiring correct and the connections are tight.

 

[dabear3428]

the issue points out that you have current flowing in the ground and as others have stated low levels of current on the ground are not ideal but are not to problematic. so step 1 is find out how much current is flowing on the ground. step 2 determine if it exceeds an acceptable level (0.004 - .006 amps). if it exceeds this level step 3 is find the problem and the problem could be anywhere from the service to the equipment being used. if less then it is less likely to cause harm but things change and it could get worse and i would check it from time to time.
or you could put in a gfi circuit breaker on that circuit

 

[sdelivery]

Remove the outlet strip and start over.

 

[markba633csi]

One of the two grounds probably wasn't making good contact, either from paint, or corrosion, or flaky crimp lug

 

[FOMOGO]

Check that the ground for that circuit in the main panel is tight. Mike

 

[SLK001]

Check that the ground for that circuit in the main panel is tight. Mike

Also, check the ground rod where the service enters the house/shop.