I am living in an about 30 years old apartment in China.

Sometimes when I am touching my Mac Book (aluminium case) I would get little electric shocks. I measured the voltage between my Mac Book case and ground to be roughly 10V, there is a current of around 1mA constantly flowing through me. :/

Another weird effect is, when I am using an LED light in my room, there constantly is a voltage of 30V even when the switch is turned off!! That seems to be some serious ground loops!

When I plug my electric guitar, I am also getting some slight shocks while playing.

So I started to make some measurements with my multimeter.

I found out that when I measure the voltage between the ground pole of an electric plug with a metallic water tap in my room, there is a potential difference of nearly 100V (!). I also measured one phase to ground to be around 120V and another phase to ground to be around 100V, so none of them are being "neutral".

Now the question is: How do I resolve this issue?

I am already using a wire to connect the case of my laptop manually with the metallic water tap (that makes most sense to me to call "ground"). Like that at least I can partially get rid of the little shocks through my body. Now, what would happen if I connected the ground pole of the electric plug (that I have measured to be at 100V) with my water tap? Would that elevate the ground for the whole apartment to "zero"? Or would that be very dangerous?

Don't worry, I will not try it out until I am sure about what I am doing.

  • \$\begingroup\$ This question might be a better fit on Home Improvement than on EE. \$\endgroup\$
    – The Photon
    Mar 22, 2016 at 2:51
  • \$\begingroup\$ First thing is to (have someone) check the ground connection in the distribution panel. \$\endgroup\$
    – RJR
    Mar 22, 2016 at 3:17
  • \$\begingroup\$ Did you check cables inside the plugs? Maybe electrical technician wired ground and neutral cables together in one of the plugs. This might cause problems in long terms. Two things you can do; 1- Detach ground wire 2- Install a new ground wire. Option 2 is way much better but hard to implement. Option 1 is the easier choice. You can avoid getting unnecessary shocks, but it may be dangerous in higher loads. \$\endgroup\$
    – Hammers
    Mar 22, 2016 at 7:04

1 Answer 1


You should check wiring, if you have three wires in the socket, then it worths to inspect and see what's wrong. Normaly the water pipe is connectected to the same ground, so there should be no voltage diffeence, but is meant to connect water pipe to ground for safety reasons, not to take ground from pipe.


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