While I was replacing a switch, I noticed that my screwdriver tester lit up (it can detect 100V to 240V) when I touched it to the earthing wire. Then by testing the supply with my multimeter I got this result: the ground and neutral wire have no potential difference nor do the live and ground and earth have any potential difference. I must specify here that I have a cheap multimeter that doesn't have LoZ mode hence I wasn't able to make any further diagnosis whether it is ghost voltage. By all this now Iknow that the earthing is not proper but I still want to know what was the reason that the tester detected voltage but multimeter did not?
Electrical – Can screwdriver tester detect ghost voltage
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Best Answer
Yes.
A "neon screwdriver" has to operate at very low currents for both safety (you don't want to give the user a shock) and functionality (the capacitive coupling between the user and earth may be weak) reasons.
Therefore it can detect voltages that are only weakly coupled, for example by cable capacitance.