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I have decided to add another plug outlet near an existing blind outlet box. Unfortunately I've found that the existing one doesn't have ground since it's an old building, but that's a problem for another day.

After connecting the new outlet, the wiring was as follows:

socket L---L wire L---L house wiring
socket G---G wire G     no wire
socket N---N wire N---N house wiring

However, using a tester screwdriver, the ground appeared live. Assuming that it's likely the socket that's the issue, I disconnected the socket ground, however the wire still appeared to be live. There was no load connected to that particular socket when testing.

Additionally, disconnecting the wire and using an auto-ranging multimeter between ground and live did not show any connection.

Is it just inductance screwing with me? A bad wire (it's solid core if that changes anything)?

I'm well aware that ground should be there and connected, but at this point I'm just moving an existing device to the other side of the room and it will remain on the same circuit as it's been for years.

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    \$\begingroup\$ It's normal. It acts like an antenna, it can light your electric tester, but if you connect some load on it, it won't give any power. \$\endgroup\$ – Marko Buršič Nov 2 '19 at 16:23
  • \$\begingroup\$ 99.9x% likely it's what Kevin says. NEVER assume it's 100% likely - but investigate with this cause in mind as most likely. \$\endgroup\$ – Russell McMahon Nov 2 '19 at 16:34
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Most likely it is capacitative coupling from the other conductors in the cable.

Within the cable the live, neutral and ground are physically close together and capacitance will exist between them. Even though the value wil only be 10' of picofarads per foot this can cause a voltage to develop on an open wire - the earth in your case. Because of the low capacitance the amount of current available will be extremely low but if your tester screwdriver is a typical neon type it only needs a few microamps to cause it to glow. If you measure the voltage with a meter the voltage will drop significantly and will probably only be a few volts.

In a similar way I have seen fluorescent light tubes glowing slightly even when the power switch is off for the same reason.

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  • \$\begingroup\$ This appears to have been the case - I have checked the other existing wire (also with unconnected ground) and once the load has been disconnected, ground wire lit up the same. A lotta worrying over nothing but better that than a house on fire. \$\endgroup\$ – Sašo Nov 2 '19 at 16:56

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