# Determine if wire in switch box is safe to re-purpose?

I need to pull a neutral wire to my light switch for a smart switch. It's presently switching an outlet that I don't need switched, and the other side of the outlet already has unswitched power. My plan is to use a smart switch, which requires neutral, to control a different device wirelessly.

I can't feasibly run a new wire, because the wires aren't run through conduit. Instead, my plan is to repurpose the switched wire to get neutral from the outlet.

The switch, which controls an outlet has two wires, one black and one red. The switched outlet has a white neutral wire, plus the red and black wires that I assume run directly to the switch.

I've completely disconnected the red and black wires from the outlet and the switch. The black wire is measuring 120V AC when measured against ground using the box as ground, both at the outlet and at the switch. Using my DMM, the red wire is measuring 24V AC with respect to the box/ground at both sides. I assume this is a ghost voltage caused by induction from the charged black wire over to the floating red wire.

Our house is ~100 years old and this particular switch seems to be run using armored cable (note the paper wrap around each wire.) There are literally only two wires in the switch box; no wire nuts.

If relevant, we do have some old knob and tube wiring active, but I'm pretty confident there's none on this circuit.

Is there some way I can determine with enough confidence that the red wire isn't connected elsewhere such that I can know it's safe to connect the red wire at the outlet to netural?

• Are you sure it's AC and not conduit? Dec 18, 2016 at 21:07
• Also, are you sure there isn't another junction box between the two? Dec 18, 2016 at 21:08
• @ThreePhaseEeel There's clearly something in between feeding the black wire 120V; given that I'm getting 120V on it when both sides are connected. Similarly, there's clearly something connected to the red wire in between. Dec 18, 2016 at 21:29
• @ThreePhaseEel I don't understand your first question. Typo? Dec 18, 2016 at 21:29
• No, I'm asking because armored cable isn't made in red/black. Dec 18, 2016 at 21:59