Knob and Tube Wiring Question


Old 05-19-07, 08:40 PM
Thread Starter
Join Date: Oct 2004
Location: USA
Posts: 114
Knob and Tube Wiring Question

I am updating a 1910 vintage craftsman style home that still has some knob and tube wiring and have a question about whether it may have been customary to share neutrals rather than home run two wires for each circuit.

I am working in the attic which feeds the second floor with two circuits (breakers). For most of the wiring I can replace everything with NM-B even in the walls. There are a couple of branches where I cannot and what I am doing is joining the old know and tube wires that come out of the wall into the attic with the NB-B in a grounded metal junction box.

Today I was working on a branch circuit of a few outlets. There was no power to the line. I needed to hook power to the branch temporarily to use an outlet and I did not pay much attention to which wire was the Neutral and which was Hot because it was a very temporary and and I figured the circuit was isolated to a couple of outlet. When I applied power, I tripped the breaker to the second circuit in the attic.

I took out my tracer and verified that I had indeed connected the hot of my temporary feed to the neutral of the branch circuit. What this means that the neutral of this circuit is somewhere in the wall connected to the neutral of this second circuit because there is not other visual connection in the attic.

After the long winded description - the question is would it be common to see these neutrals tied together in more than one location? Is my diagnosis of why the circuit blew plausible?

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Old 05-19-07, 09:22 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
With knob and tube wiring they did some very strange things, including wiring switches in a funny manner. You should not be surprised at anything you find.

My advice, and you would be wise to heed it, do not attempt what you are proposing. Do not attach new wiring to existing knob and tube. Either leave the knob and tube intact as it is, or completely replace it.
Old 05-25-07, 09:25 AM
Join Date: May 2007
Location: California Central Sierras
Posts: 29
Most inspectors and building departments will not allow any repair to knob and tube anymore, the stuff just aint safe. Pull new cable and save your reputation and the building.

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