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So basically the case of my washing machine was causing a mild shock on touch when it was connected to the wall outlet. I took a multimeter and checked voltage from the case to the ground, and it turned out to be about 30V . Initially I thought that it's some kind of short in the machine, but I figured that I can check voltages in the outlet just in case, and lo and behold, everything seems to be wrong in all outlets in the whole bathroom. I don't know which endpoint is live and which neutral, because it's an old house and the order of these is all over the place, but my results were:

  • 1 > 2 = 230V - that's normal
  • 1 > ground = 8V - hmm...
  • 2 > ground = 30V - hmmmmmm...

I know I need electrician and I will get one, but just out of curiosity - what does it tell me exactly? I expected one result related to the ground to be much higher than the other, how it's possible that the difference is so low if the difference between #1 and #2 is so high? How it's even theoretically possible?

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    \$\begingroup\$ maybe the ground terminal is not really going to ground, but somewhere else \$\endgroup\$
    – MPA95
    Commented Mar 1, 2020 at 22:36
  • \$\begingroup\$ But would that explain only 22V difference between both wires and ground and 230V between them? Maybe someone could draw a circuit and explain how such values could be possible, that would be very informative because it's hard for me to wrap my head around these results. \$\endgroup\$ Commented Mar 1, 2020 at 22:46
  • \$\begingroup\$ Read this. It's likely that it's an IEC Class II arrangement and that's what you are measuring. And yes, you can feel it, too. \$\endgroup\$
    – jonk
    Commented Mar 1, 2020 at 22:48
  • \$\begingroup\$ @jonk - You should make your comment an answer. I would guess you are correct. \$\endgroup\$
    – MadHatter
    Commented Mar 1, 2020 at 23:28
  • \$\begingroup\$ @MadHatter Then I'd have to write about a topic I'm only "slightly dangerous" (in terms of breadth of knowledge.) Plus I'd have to write my usual "long" discussion so the context is in place. And today I'm busy working on other projects I need to complete in short order (the self-employed don't have weekends and wouldn't know what one looked like if it hit them in the face.) So I probably won't have much time to write until Tuesday. And by then, better people than me can write it up well. \$\endgroup\$
    – jonk
    Commented Mar 1, 2020 at 23:34

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The most likely explanation is that your "ground" isn't actually connected to anything; it's simply floating. There may be a bit of stray capacitance between the ground wire and the live and neutral, if only because the wires are running together in the power cord. The leakage through that capacitance will be enough to show as a small voltage in your multimeter.

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    \$\begingroup\$ My guess is pretty much what you say, except that I suspect they are also pulling 120 VAC from one hot and neutral to develop IEC Class II power to operate the "front panel" and that they are using an intentional Y-type capacitor, rather than just stray capacitance. \$\endgroup\$
    – jonk
    Commented Mar 1, 2020 at 22:51
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Some jackass installed a grounded receptacle so they would have the convenience of being able to plug in things which require grounds. However they did not actually hook up the grounds. That's why they ring out to nothin', as SimonB says.

The small voltages you are seeing are because you are using a DVM (most cheapie DVMs are very high impedance, which is generally a desirable feature, but is sensitive to phantom voltage). If you used a low-impedance meter that voltage would disappear.

Anytime you're dealing with old wiring like that, your first priority is to fit RCD (GFCI) protection first on anything near water (dockside, pool, bathroom, kitchen), then on lesser damp locations (basement, garage, outdoor outlets), then on the rest of the house. For human protection you want 5-6 milliamp trip threshold. That is too sensitive for a whole house, so it needs to be applied circuit by circuit. Euro-style "whole house RCD" is necessarily a weaker 30 milliamp trip threshold. It is better than nothing but I would want supplemental protection on the above priority list.

What's the difference, 6-30 ma? That is the "Stun zone" where it's unlikely to kill but likely to stun. When you stun, you fall, and if your face lands in water, that's a kill. It's called "electrical drowning". Happens all the time.

Your second priority, to do after or (if unable) instead of RCD/GFCI, is proper grounding. Most countries around the world crib their electrical codes from each other. In 2014 the US NEC liberalized the rules, to allow retrofitting a ground wire on any circuit. That means the ground wire can be simply run alone, and can even go to an intermediate point that has a thick enough ground wire. That may have made it to your country, in which case, go crazy :)

I am of the view that ground fault/residual current protection is pointless for an installed, non-movable machine with a metal chassis that protects all the electricals; and which also has a competent ground back to a panel with a proper neutral-ground equipotential bond. Any ground faults will reach the metal chassis/shield before they could possibly reach a human, and be directly routed via the ground and N-G equi bond back to neutral. A minor leak might just waste power; a bolted fault will return a massive amount of current through the competent ground, causing an immediate breaker trip.

The purpose of the N-G bond is at least twofold:

  • to return fault current to neutral (remembering electricity wants to return to source not ground, actually the N-G bond is what makes ground a desirable return); and
  • to prevent the otherwise-isolated electrical system from floating at some insane voltage due to a transformer leak.
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