How can there be 0 volts difference and yet I can feel electrical tingle? [closed]

Question

While the background for this question is quite practical and probably off-topic for this site, what I'm asking here for is why this happens and not how to fix it. I want to understand the electrical forces involved, not just get a quick fix.

With that out of the way.

Grounding. I've never understood it. It always acts in mysterious ways.

Case in point: my latest adventures with trying to install a dishwasher.

First of all I live in a flat in an older house which has no grounding in outlets. This is Latvia, so 230V/50Hz. After installing the dishwasher I realized that when I touch the sink and the dishwasher at the same time, I can feel a noticeable and unpleasant tingle. It's not the full 230V, not even close, but still noticeable enough to be startling.

I tried measuring the voltage difference with my trusty cheap old multimeter, but it came out as 0V... or at times even -1V, which makes no sense. Putting the multimeter directly into an outlet shows around 230V as expected, so it's not broken. Measuring between the plug pins and the body shows that they aren't connected, so there is no broken insulation.

I also have one of those indicator screwdrivers. When I touch the sink or the dishwasher individually with it, it doesn't glow. But when I touch my other hand to the other object, it glows.

Weirder yet - if I plug in an extension cord which has grounding, into an outlet that doesn't (it physically doesn't have grounding connectors), and then connect the grounding pin, myself, screwdriver, and the sink - it glows! And if I unplug the extension cord, it stops glowing.

The same effect exists between desktop computer cases and the centralized heating pipes/radiators. I've even noticed it with my old laptop when it's connected via a power adapter. And that adapter only gives out 19V!

To try and combat this I brought in a cable from outside my apartment which is connected to a grounded breaker/meter box. Or at least that's what the rumour says. At the very least I can confirm it's connected to the neutral.

Measuring between that ground and the sink now gives me around 6V... and also a tingle. The screwdriver behaves the same as before.

Slightly worse, since my oven/stovetop are also connected to the same outlet, they too have now started to give a tingle when touching them at the same time as the sink. So, basically I would be better off without the grounding in that outlet.

I'm lost. How can there be such a noticeable electrical tingle, when the voltage measured is 0V? Why does the screwdriver not glow when I touch it to the sink, but starts to glow if my other hand touches a disconnected wire - but only if that wire is close to electrified wires?

Answer 1

Devices with earthed mains plug such as computers and dishwashers have a mains input filter, with so called Y capacitors from Live to Earth and Neutral to Earth.

If you don't plug the device into Earthed mains socket like you are supposed to, all parts that should be Earthed are floating and the filter Y capacitors create a capacitive divider, so the parts that should be Earthed has capacitively coupled half mains voltage of 115 VAC (assuming 230 VAC mains) on all metal surfaces.

The current drive ability of one device is quite limited but still you can feel it.

Since it is the device that now drives the Earth pin on the extension cord it will energize all other Earthed devices on the extension cord too, even if those have no filter Y capacitors inside them. If the other devices do have the filter Y capacitors, then each device adds up and the Earth pin is driven more strongly.

Kitchen is one place there really should be Earthed sockets. Even really old houses (40 years old or mode) have had Earthed sockets in the kitchen and bathroom in many countries. Consider upgrading the electrical system for safety.

Many devices have a statement on them or in the manual that they must be connectes to an Earthed outlet. This is one reason why. Water and electricity are also a dangerous combination so consider having a grounded socket for it.