Ask Electronics

Definitely change the plug into one that has earth as well, and make sure the motor body is grounded to the frame, and that the frame is grounded to the earth connector in the new plug

The limits we look for in these cases (in germany) are:

1. less than 50V AC and
2. less than 0.5mA

(This is for touchable metal parts, that are not connected to earth)

So yeah, I'd try to avoid touching the motor spindle, but with that low of a current it shouldn't actually be a problem as any current flow at all will make the voltage drop significantly.

You can try grounding as many of the metal parts as possible, but the motor shaft will likely be difficult

Your last image shows that your sewing machine plug has no earth ground. I’m not well versed in sewing machines enough to know if this is typical for sewing machines, but typically any appliance with no earth ground will insulate the user from either conductor.

You cannot count on the neutral wire to safely ground anything that the user touches.

Your readings indicate that there’s a small amount of voltage coupling onto the housing. Voltage alone doesn’t indicate much if there’s no current behind it, so it could be safe, but as another user indicated, you probably want external metal bits to be earth grounded. That’s the whole point of earth ground.

30V won't kill you. Even with 170V it might not cause much harm, since the current is in micro Amperes. I hope you have a good MCB, and even even good curcuit breakers. If they are present and they don't get tripped while operating or testing, it should not be lethal.

That said, you don't know the reason for this leak. Better to take it a repair shop. If you like doing it yourself open up and see if there is any visible tear on power line insulation. If nothing is visible if can be some issue with winding of motor, some other component.

You can use it with gloves, a good foot wear, and a good set of circuit breakers, if it has to be used, but I won't recommend taking such risks. Since it is an old machine I would say you get it repaired if possible.

I would say you're right about it being just parasitic/capacitive current. And 4.1 uA and 43uA is thousands of times smaller than what would be dangerous, so that's a no for the kill you part. If you're very woried about the reading, you could add a 10k-100k Ohm resistor between the machine body and the ground while measuring, if voltage drops to near zero it's fine.

If you decide to add a ground, please don't do it with a second plug. Replace the cord with a 3-core one, attach PE to both the machine body and motor.

I would be pretty wary of using it with that amount of voltage. If the electricity routes through you, it would probably give you more than a good buzz.

Based on the fact that it made your fingers tingle before you replaced the motor, I doubt the new motor or your installation of it is the cause of this issue. You probably have some kind of short inside the machine itself. Best bet is to crack open the machine (when unplugged, obvs). This could be the most dangerous part - make sure you can identify capacitors on the circuit board and find a youtube video about safely discharging them, as capacitors can store dangerous amounts of electrical charge even when the circuit is unplugged, and discharging them accidentally can fuck you up. Then look for obvious loose connections. If you don't see that, you will have to start searching for the short. Set your DMM to measure resistance. Search the motor component with one lead and the rest of the machine's circuit with the other. As long as resistance is a real number, you have a closed circuit and the short is on the circuit the leads are on. When resistance jumps to infinity, you are no longer in a connected circuit, and the short is somewhere else. Often, shorts will read as significant amounts of resistance, as the marginal connection between two components is not enough to allow free-flowing current. Note that this creates a new danger - even if you don't electrocute yourself with the machine during use, it is possible it will catch on fire as electricity running through a marginal short heats up the components. If you are lucky, you can identify the short by noting the leads have non-zero resistance in one spot, but 0 reistance upstream and downstream of that spot. Then you might look real close and see a loose wire or a burn mark. But maybe this is just an expected bit of resistance that was designed into the circuit. It's a bit of an art, takes some patience, and if the solution isn't immediately obvious, there is about a 70% chance you are wasting your time.

Ideally, as the other user said, you would also install a ground during your troubleshooting so you don't electrocute yourself in the future if it happens again.

Thats a weird sympton. There usually isn't alot of electrical wiring in that kind of machine. Have you checked the wiring and socket for the light bulb? Maybe something with the power switch?

Seems unlikely that the new motor is bad in the same way as the old.

Did you use the old mounting hardware to mount the new motor? Maybe a too-long screw?

That's my only guess, I'm not very good at this stuff.

@einfach_orangensaft Measure current. Might be capacitive through capacitor in motor. And check your GCD.