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Old 11-07-2009, 09:01 AM   #1
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Knob and tube neutral question


Hello all.

I have a question regarding knob and tube. I am finishing my basement, and I have uncovered knob and tube running between the floor joists of the first floor. Most of these wires, running in parallel, run about 20 feet and then suddenly terminate (they dropped below the basement ceiling and then were cut off- just stubs hanging down). I figured they were abandoned. My house is 100 years old and has had a number of upgrades over time, and several circuits are abandoned. I do think most of the recepticles and lights are powered by the original knob and tube. Anyway, I recently had an electrician upgrade my main load to 200A (from a Federal Pacific 100A box), and I asked him if I could remove the old wiring (am planing to run in-floor radiant heat in those joists). He checked the wires and said there is no current in the hot wire but that it was impossible to tell if the neutral was being used to return other circuits to the panel. This made no sense to me. Surely there must be some way to tell without cutting the cable- if current is returning though that neutral, couldn't I measure it with a volt/multimeter?

Anyway, I appreciate the help.
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Old 11-07-2009, 09:28 AM   #2
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Knob and tube neutral question


you can measure current with a clamp on meter but if that conductor is not being used at that moment, it means nothing to read 0 current.


about the only way to really tell if it is an active circuit is trace the thing.

If you are at an end of the circuit and you can see the ends of the wires, you know that that part is not active. You then need to track it back to any possible junction points and then trace outward to see where the splice goes and determine if that is an actively used circuit. Obviously the section that dead ended can be removed from the circuit at the junction point.

If you cannot see the end of the conductors, you could easily cut an active circuit.

it is just a matter of a lot of labor to do this but it sounds like it needs to be done to assure yourself you are not cutting an active circuit.
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Old 11-07-2009, 09:34 AM   #3
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Knob and tube neutral question


boy this post sounds familiar... been there done that!

what i found with knob & tube is that you must trace it 100% visually. because very often someone would have scrapped off some insulation, wrapped a wire around it and then go off to service some load. how would you know such a rat-nest wiring job exists unless you visually inspect the ENTIRE thing? don't be surprised if you find stuff like that, burried junction boxes, burried connections not even in a junction box etc.

its definately worth your time to upgrade when you are able. your future home sale will depend on this greatly.

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