Knob and tube wiring is common in our area. Ideal used to make a contact pocket voltage tester (61-050), it is no longer available. I used it to identify the hot conductor. Does anyone know of another method to find the hot conductor?
Showing my age now...long before the 'non-contact' age, internet, cell phones, cordless landlines, and a whole lot of stuff........
Locate a 'ground' somewhere within the building, or if that's not possible, a known neutral point. even if you have to go back to the service entrance. Connect a suitable length of #12 stranded THHN or equal to said point & stretch it out to the location you want to test. You then have to skin a test point on the K&T conductors and use whatever tester (wiggy, digital, etc).
I did not say it was easy or quick; but it works. If I had to do it today, I'd pull out the non-contact, I have an Ideal, Gardner Bender & a TIF. Any of those are available thru WWGrainger, most electrical supply houses and the big boxes. Look in Tools for Electricians in the right hand border ads right here also, you may find one.
Back in the olden days we used neon testers. They could give you some bad indications but I am not sure a ticker is really any more reliable. I still would not stake my life on either of them. They are just indicators, not testers (to steal the language of U/L)
You never saw the neon tester pen? They typically have a small screwdriver on one end and a pocket clip. The clip is the "ground" and you are the ground electrode system, capacitively coupled to the earth. There is a megohm resistor there so you won't see circuit current. If you touch the screwdriver to a hot lead, the neon lights. Sometimes you just have to be close to the hot lead. They may not light 100% of the time, particularly if you are very well isolated from ground, like up in an attic on dry truss chords but they usually work OK.
I will root around and see if I can come up with one.
Non contact volt testers can give neutrals a hot indication where part of a circuit is chopped out and the return is through a load as a result of a bad assumption. When it comes to K&T I treat all the wires as hot until I am the one that cut it and I am not perfect so be careful the neutrals can be very dangerous too.