I have a < 10 year old house. And today I wanted to use the 2nd lamp outlet in the living room, and even though it was turned off, I got hit by electricity. I am in 230V, 50Hz country (Measured 227V). Measuring, I can see that I had 72V AC when the other lamp outlet (should be independent) was on, 50V AC when it was off. When I disconnect the mains wire for all my home TV/Stereo etc, the 50V goes up to 55V.
The voltage from the phase was measured both to Neutral and to GND. It is supposed to be air gapped when off according to all electricians I ask. And if it was connected, it should have 230V.
The other lamp outlet and this one, both have correspondance switches (i.e. turn on/off on either side of the wall). So their wires do run parallel for like 7 meters after the on/off switch. The probably shares the same phase.
I have received a 2 theories, one is the voltage is generated by electromagnetic induction.
The other that Switch mode PSUs are sending spikes out on Neutral through capacitors, that might be out of phase and frequency, such that the Neutral is where the power is. This sounds unlikely as there is around 1.2V AC between GND and Neutral.
I can say that I have switch mode PSUs on my wiring. And I have been told even my LED bulbs do have switch mode PSU.
Since a turned off lamp outlet, by all legal designs of correspondance of switches I have seen, should be air-gapped to the phase, I see no explanation where this ghost voltage is coming from.
I do consider shorting it to N so see if a fuse will be triggered (13A fuses). My electrician witht he switch mode PSU theory expects no fuse will blow.
Can I create a poor mans oscilloscope with an Arduino, a 47MOhm + 1 MOhm voltage divider and connect N to 0 and the divided voltage to A/D pin ? Use bluetooth module for data-connection to PC. Hoping to see irregularities/spikes in voltage to explain things - Supposedly I can get up to 3000 samples/sec, which should be more than sufficient for 50Hz. Should I use battery power, or just a 5V PSU ? The PSU probably uses the same Neutral anyway ?