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I have a box with three conduits. These are in-wall/under the floor steel conduits from an apartment built in 1950. One conduit has hot and neutral wires coming from panel. The second has hot and neutral going to a nearby outlet. The other conduit has two wires (supposedly hot and neutral), and I don't know where it goes.

Regarding that unknown conduit, I unplugged the hot and neutral going into that conduit and there was no effect on any outlet (light, switch, etc.). I thought it might be an outlet that was covered during some renovation.

However, very surprisingly, when the hot is connected, the neutral is energized meaning either there is something connected at the other end, or both wires are connected/touching somewhere along the conduit or end box.

Given that I have no idea where it goes since there was no effect at all when disconnected, and these are the only two wires in that conduit, what can be done to: confirm if that energized neutral is a return neutral, or if that energized neutral is touching/connected to the hot at some point; investigate where this conduit goes (might be something covered).

Please note that that neutral only gets energized when the hot (of the same conduit) is connected to the hot from the panel.

Thank you.

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  • How are you determining that the neutral is energized? Look for blank wall or ceiling plates.
    – JACK
    Jun 16, 2021 at 16:27
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    It is not suppose to, but it might go to another apartment. Next door/wall might be tearing their hair out trying to find why an outlet lost power for a bit.
    – crip659
    Jun 16, 2021 at 16:30
  • Are you sure this is not a switch leg? A hot and switched hot possibly.
    – Ed Beal
    Jun 16, 2021 at 17:01
  • @JACK I have a non-contact tester pen. I guarantee it's not a false read because I took both wires far away from box.
    – igorjrr
    Jun 16, 2021 at 17:57
  • @Ed Beal no idea. There is no switch nearby, and this is a receptacle. Could be, maybe they hid the switch in-wall, and left both wires connected. I'd like to find there this switch is.
    – igorjrr
    Jun 16, 2021 at 17:59

2 Answers 2

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The mystery conduit probably runs to a switch which was installed to control that outlet.

Look for a wall switch in or near the door to the room containing the outlet. Try to confirm that the switch apparently doesn't control anything else. Flip the switch and check if the mystery neutral is still energized.

If you can identify that the switch is intended to control the outlet, then wire the junction box like this:

Connect power conduit hot (black) to switch conduit white. Mark this white wire with colored tape or paint to indicate that is not a neutral wire.

Connect switch conduit black (switched hot) to outlet conduit black.

Connect power conduit (neutral) white to outlet conduit white (neutral).

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  • It is very far from a door (it's a studio, actually, no doors other than entrance and bathroom). There is no switch nearby.
    – igorjrr
    Jun 16, 2021 at 18:02
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A professional electrician might use a signal tracer in this case. The device places a signal on the wire, and can be followed through building materials. Perhaps you can hire someone, or borrow the tool at a local tool library.

Wire tracing tool

You could also measure resistance from the hot to the neutral. And why not just let these wires remain disconnected, perhaps leaving a note in the box regarding the situation for future workers?

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  • There are tool libraries?
    – jay613
    Jun 16, 2021 at 16:38
  • @jay613 there are stores that do have programs/sections like tool libraries. canadiantire for one.
    – crip659
    Jun 16, 2021 at 16:57

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