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?