In knob and tube wiring, how to identify neutral wire vs a dead wire?

Question

I'm in the US, Ohio if that matters.

I have an old house with many circuits still on K&T wiring. I haven't been able to find information on how to identify a neutral wire - most guides just tell you how to identify hot wires, and whatever is left must be neutral.

Some of my K&T wires are disconnected but still in the wall.

Is there a way to identify which ones are neutral vs the ones that are simply disconnected from the electrical box in the basement?

Thanks.

score 3 · Accepted Answer · answered Nov 19 '18 at 08:09

Plug in an extension cord, and bring its socket end up to where you're working. Measure voltage from extension cord "hot" to the mystery wire. 120ish volts - it's a neutral. Significantly less - phantom voltage on a dead wire.

To sanity check what "120ish" volts should be, measure hot v neutral on the extension cord itself.

score 2 · Answer 2 · answered Jul 01 '18 at 04:42

I have worked on many old. K&T homes the best method is with a wiggi, not used much today but a low Z meter will work. Just as well for residential voltages, in my experiance Watch out, I had a home in Dayton that was totally backwards , Wayne avenue. 2 houses from the theater if it is still there. One conductor will be connected to the hot or 120v line, the other is connected to ground, the best method I found back then when analogue meters were the standard was to measure the voltage from a water pipe to one wire and then compare this with the pipe to the other conductor the highest voltage was the hot.

score 0 · Answer 3 · answered Apr 28 '18 at 21:50

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I am assuming you don't have a circuit tracer, but that would be the method I would use. The only other method I could think of would be to check it with a continuity tester and a really long wire. You could connect the wire onto the neutral bus, turn the phase conductors off, then go around and check each conductor. The ones you get a "ring" from are the connected neutrals. Everything else is a hot or a disconnected wire.

This seems a little awkward but you are going to have to get some sort of address signal to ring through the neutrals. Maybe someone has a different approach.

answered Apr 28 '18 at 21:50

Retired Master Electrician

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You may get a ring from a hot, via a load. – Harper - Reinstate Monica Apr 28 '18 at 22:20
That's why we turn the phase conductors off or disconnect them so we can't get a ring through. – Retired Master Electrician Apr 30 '18 at 14:10
That doesn't help. Think of any load as a resistor between hot and neutral. – Harper - Reinstate Monica Apr 30 '18 at 15:10

score -1 · Answer 4 · answered Apr 29 '18 at 04:20

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Take a loose piece of wire and connect one end into the neutral bus bar in panel. Take the other one with you to the test site. First check for voltage. If you have voltage you have a live wire and presumably in use. No voltage. Check for continuity. No continuity you have a dead wire. It can come out. Zero ohmes. You have a good neurtal. Some ohmes present you are on a switch leg turned off.

answered Apr 29 '18 at 04:20

Paul Logan

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Been there but disagree, I purchased a cape cod that was totally wired backwards! If an older as K&T would suggest there is NO ground buss. – Ed Beal Jul 01 '18 at 04:47
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My comment was intended as a help from someone with considerable experience, (not unlimited experience) not a flag to be shot at by people like you. You may remember the saying of old: If you don't have anything good to say, keep you mouth shut. – Paul Logan Jul 08 '18 at 15:45

In knob and tube wiring, how to identify neutral wire vs a dead wire?

4 Answers4