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I live in a century house whose electrical was last worked on in the 1960s at the latest. Without opening a wall, I’d like to make some deductions about the odds of having in-service knob and tube wiring.

My multimeter has a NCV detection feature that alerts + / - 4 inches or so from lightswitches and receptacles, and also detects voltage in the wall along a logical line (e.g. up the stud bay from the lightswitch but not the next bay over).

Is it fair to say that if I follow the NCV detector beeps from a lightswitch or receptacle, and find two parallel tracks a foot or two apart, I probably have Knob & Tube?

Is the inverse true? If the NCV only alerts along one 6-8 inch wide line, is that a pretty reliable indicator that both conductors are closer together than K+T would be and so I likely have some later style sheathed wiring?

newcoder
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Yes your testing plan can work but you will need a load on the circuit to be sure. With no load on the circuit the NCV will only detect the hot, if the circuit is daisy chained as long as the last receptacle or outlet in the chain is loaded there should be the return voltage on the neutral and the tester should detect it. No load and only the hot will be detected so it would look like it was updated but may be K&T. I have always liked using a plug in light but today’s LED’s may not have enough to be detected the field may be weak, a 60w lamp or a hair drier On low will work well .

Ed Beal
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