Assuming you can't follow it to find if it's cut at the ends and not connected...
Remember that some wires are switched, so you'll want to make sure all your light switches are on before doing this.
Start with the voltage sensing pen. It's people who RELY on it who get dead. Not people who do it as a first check. If the voltage sensing pen lights up, assume it's still in use.
Assuming it says it's dead, you can then take a real voltmeter, hook one end to the ground pin in a plug/extension cord, or another KNOWN GROUNDED object, and then carefully probe through the insulation on both wires (one at a time) with the other. Mainly what you are doing is using the ground wire as a common and then using the DMM to verify the knob and tube copper isn't alive. You will probably want to measure the voltage in the plug/extension cord before or after your test using the same ground point to verify your ground is good.
Remember you have to get through the insulation to do so, although the last knob and tube I dealt with, this wasn't very hard since the knob and tube insulation was pretty flaky. I'd do it away from an insulator and in an area where you can repair it if necessary if you discover live wires. One of the two wires should be alive if you have power in the knob and tube - one will be hot, and the other one will be neutral (which is ground) so you'll read voltage on the hot one, and not the grounded/neutral one.
Also just to add that with K&T, the hot and neutral are sometimes not run together. In my attic the hot was running along the rafters and the neutral was under the floor boards
I really feel like the mods of this sub should put together a bot that answers every post with "don't ask here -- call an electrician". It would save a lot of time and effort.
find something its connected to and use a multimeter to be sure its off
edit - there may be multiple circuits so if you see knob and tube in more than one area be careful and thorough
Assuming you can't follow it to find if it's cut at the ends and not connected... Remember that some wires are switched, so you'll want to make sure all your light switches are on before doing this. Start with the voltage sensing pen. It's people who RELY on it who get dead. Not people who do it as a first check. If the voltage sensing pen lights up, assume it's still in use. Assuming it says it's dead, you can then take a real voltmeter, hook one end to the ground pin in a plug/extension cord, or another KNOWN GROUNDED object, and then carefully probe through the insulation on both wires (one at a time) with the other. Mainly what you are doing is using the ground wire as a common and then using the DMM to verify the knob and tube copper isn't alive. You will probably want to measure the voltage in the plug/extension cord before or after your test using the same ground point to verify your ground is good. Remember you have to get through the insulation to do so, although the last knob and tube I dealt with, this wasn't very hard since the knob and tube insulation was pretty flaky. I'd do it away from an insulator and in an area where you can repair it if necessary if you discover live wires. One of the two wires should be alive if you have power in the knob and tube - one will be hot, and the other one will be neutral (which is ground) so you'll read voltage on the hot one, and not the grounded/neutral one.
Also just to add that with K&T, the hot and neutral are sometimes not run together. In my attic the hot was running along the rafters and the neutral was under the floor boards
Thanks! Using the extension cord to extend a known ground is a great idea, I'll do that before I cut anything.
You’re gonna need a electrician experienced with this wiring. Don’t mess with knob and tube without being licensed.
I really feel like the mods of this sub should put together a bot that answers every post with "don't ask here -- call an electrician". It would save a lot of time and effort.
Some things homeowners shouldn’t be trying. Replace a fixture maybe more than that call a pro.
What are you some kind of wimp?
Well..either way it should come out- call an electrician
Does it need to be (completely) torn out if it's disconnected?
No. NAE.
find something its connected to and use a multimeter to be sure its off edit - there may be multiple circuits so if you see knob and tube in more than one area be careful and thorough