Terminating Knob & Tube


Old 09-06-14, 06:10 PM
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Terminating Knob & Tube

I'm replacing some knob and tube outlets with GFCI outlets. I'd like to terminate the branch that is on that run. I've been doing some research and found this:

Terminating Knob and Tube

I was taught, (METHOD A) leave a length of about 8 inches past the last knob, tape the cut end of the conductor, wrap the conductor tightly around the knob, cover the whole mess with several layers of Super 33+.

An inspector is asking me to, (METHOD B) leave a 12 inch length past the last knob, double the conductor back over itself and tape the cut end of the conductor to itself back near the knob.
What To Do With Knob And Tube Wires

Don't forget to turn off the power to the wires you will be working on, and check that there is no current running through them after the juice has been cut by using a power tester. The proper approach is to trace the individual wires back to their nearest glass or porcelain insulator, and cut them there. Tape off the end of the bare wire with vinyl electrical tape, and wrap the whole insulator with tape to ensure safety.

Article Source: What To Do With Knob And Tube Wires
What I imagine from the description is something like this:

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I could terminate it in a box, but I'd like to drywall over it (or eventually remove it all)

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Old 09-06-14, 06:45 PM
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I could terminate it in a box, but I'd like to drywall over it (or eventually remove it all)
You disconnect on both ends and abandon in place. No need to remove. If you can not de-energize and terminated in a box the box must remain accessible and the wires capped with wire nuts.

Last edited by ray2047; 09-07-14 at 08:24 AM.
Old 09-06-14, 07:47 PM
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What type of inspection was this?
Old 09-07-14, 12:08 AM
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Are you referring to the link I posted? Or just in general? No inspection on my end, just me trying to eliminate as much K&T as possible.

It seems like the double back is common in San Francisco the more I look around. I even found a couple places in my garage where it was done by previous owners. Perhaps because it's so prevalent here.

As for taping, isn't that a normal practice with K&T? Especially when when spicing or removing splices?
Old 09-07-14, 01:38 AM
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I am ASSUMING that what you have done is to shorten a knob and tube circuit and now want to terminate the end of the circuit that is still in use. If that is the case then follow the instructions that have you cut off a tail about a foot beyond the last knob and then bring that tail around the knob and tightly twist it onto the existing conductor. Then wrap that twist in the same direction with plastic tape and a layer of old-fashioned friction tape if you can find it. The plastic tape will be more likely to come loose if you do not wrap with the friction tape but it is not an absolute necessity.

Splices and taps on K&T work were soldered and taped with a self-vulcanizing rubber tape and then the rubber tape covered with friction tape to protect the rubber. It was done that way because they did not have the materials we have today.
Old 09-07-14, 06:00 AM
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Why not simply install a wire nut on the abandon end.
Old 09-07-14, 06:10 AM
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I have a few concerns here.. You are pulling out the old open space wiring.. and replacing it with? What will feed this new GFCI circuit? Will there be a ground? Make sure this old knob and tube isn't feeding other parts of your house.. when this wiring method was used, they really only needed light and maybe a fan so they usually ran it everywhere, a single home run could run a quarter of your house. And the correct way to end a knob and tube circuit it to cut the hot and neutral conductors (seperately!) 12 inches from the farthest insulator you can go.. Tape off the end well and then fold it back onto itself. Then tape it all from and including the bend all the way to the insulator. Hope that helps. And by the way, I'm an Electrician.
Old 09-09-14, 12:14 PM
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The new GFCI circuits are coming from the box with a leading GFCI receptacle on one and a GFCI breaker on the other other. I'm trying, or even considering, splicing into the K&T. Basically if I have to leave any K&T it will be for one of two reasons. A, I can't get to it or B, it's only powering a light.

I pulled out some old wallboard that needed to be replaced and this was when I was able to kill some of the K&T runs. So the question that remains is can I leave those terminated runs in the ceiling without a box? Or is it the same as running Conduit, etc, where there has to be access?


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