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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?

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  • I take it your "screwdriver tester" is one where you clip one lead to a ground point and touch the tip to a potentially-energized object to detect voltage? Apr 26 '19 at 22:25
  • Yes and the ground point is my finger. The exact structure is given in this Electronics SE answer electronics.stackexchange.com/a/96102
    – baba
    Apr 27 '19 at 10:16
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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.

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