Old house. Some wiring is knob-and-tube. All connections to circuit box is Romex. Here is what I can't figure out. I'd like advice on what it might be and how to fix it.

I shut off the breaker to Circuit 8. Voltage tester tests off. Plug in a light, it won't light at any outlet. HOWEVER, if I take a non-contact voltage tester (chirper) and hold it right up to light switch, whether switched on or off, it tests for current right next to the box. Additionally, I get a positive for current next to an uncapped neutral on the same circuit. If I shut off Circuit 18, which in no way looks to be tied to Circuit 8, then I get no current on 8.

Also, in another part of house, ceiling lights constantly burn out.

Thanks for any help and ideas.

  • Ouch, you may have a shared neutral (it's supposed to be an MWBC but it may not be). If it has a neutral problem it will send 240V to your devices. Apr 25 '17 at 20:03

OK, First a "chirper" measures the magnetic force around an ac current carrying conductor, but it does not identify the strength or the amount of power of that conductor. So you may be picking up trace voltages. Since you mention knob and tube also romex, I am assuming that it is an extremely old system and it has been modified probably more than once. Knob and tube and some older romex systems do not have grounding systems. It also means you may have a switched neutral which was legal many years ago (like 75 years).

I suspect that you are getting a certain amount of feedback power through the neutral from circuit 8 and circuit 18. When you add the comment that ceiling lights are constantly burning out it may be confirming that you are experiencing "floating" power and the variations of the power is not good for the life of any lights or equipment. For example, if your lights are dimming in the kitchen when you turn on a hair dryer in another room, that would also indicate a "floating neutral". The only other reason you would be burning out lights is that you're buying cheap lights. If you are not experienced in electrical power I would suggest professional help. If you want to try and labor through it USE EXTREME CAUTION.

The first thing they teach in electrical apprenticeship training is to always treat everything as if it were hot unless you are absolutely sure it is dead. In your case turn off the entire panel.

  • The chirper, tick tester or non contact testers use the hall effect and detect the field created when voltage is present on a wire. If the wire in question is running parallel to an energised circuit a voltage can be induced on the circuit that is off including the neutral creating a false positive.
    – Ed Beal
    Apr 26 '17 at 1:39

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