I am in the process of replacing switches in my 1920's home which was renovated in 1970. While doing so I am creating notes of what wires exist and do not exist in each box. I found a light switch where the line in connection is hot, per my Klein non-contact detector. But, when I turn the light switch on neither the load or the line wire connections are showing up as hot, but the light is on. On the light switches I looked at so far, when I turn the switch on it results in both the line and load connection as hot.
Is there something wrong with the wiring?
Best Answer
This has all the smells of a switch in the neutral wire, which is a no-no as it's a potential shock hazard for a clumsy bulb changer, and forbidden by NEC 404.2(B):
The reason why the voltage detector turns off when the switch is on is because when the switch is on, the switched wire is effectively connected to the grounded conductor, putting it a few volts above earth ground. When the switch is off, though, there's no current flowing, so the switched wire "floats" at mains voltage, which is picked up by your detector.