I apologize if I missed this info elsewhere. I have an 80 YO bungelow with seemingly healthy knob and tube wiring. The house has a combination of old and new wiring depending on when past work was done.

My question is what is the safest, code friendly or preferred way to mate the old K&T to new 14/2 wiring where needed? What is the technique for safely securing them in a junction box while maintaining their separation/insulation?

Thanks in advance for your professional advice and help.

I have never seen anything on connecting K&N to modern wiring. The old K&N is still safe and meets code as long as it is in good shape. Unfortunately the insulation may fall off it at the slightest touch. I would start near the end of it, and carefully wrap a short section in modern tape very well. I would then set a junction box near it, and make the splice to the modern cable in the box. The heat shrink tubing meant to be slipped over bare wires might be even better than tape. You could also use a plastic box and bring the K&T in through different holes. Be sure you limit any circuit fed by #14 wire to light duty and a 15 amp breaker. If there is any chance of needing more power, for the difference in price, I would run 12-2 with ground.

The above should be safe, but I am not sure of code.

The plastic box is excellent advice. Be sure to allow at least six inches of each wire in the box,both wires of the K&T and the Romex cable you are splicing to.
Assuming you are installing new extensions using Romex, cannot use metal clad cable with plastic boxes.

The most important issue with K&T is to not allow any building insulation to cover it, as this is not allowed by Code. Code still allows for K&T to remain in buildings, and to allow for extensions, but does not allow it to be covered by fiberglass or any other type of insualtion. This will entrap any heat and create a fire hazard.

A better installation would be to replace all exposed K&T, with new cable. I assume you have exposed K&T wiring in the attic and/or basement. At the points the K&T goes concealed itno a wall is where you can install the plastic junction box, and all other exposed cable wuld be Romex.

It is extremely important that all K&T wiring be protected with a fuse or circuit breaker no larger than 15 AMP. The new wire can be #14 or larger, but still have 15 amp protection.

Another important issue is to be sure of which is hot and which is neutral,you will be splicing new black and white wires to the K&T wiring, and polarity is very important. If not sure how to check this let me know.

... site http://www.nachi.org/toc-electrical.htm and check under the Knob and Tube Wiring section for info regarding connecting to your new wiring.

Thanks to you all I am much more comfortable with my situation. Th eplastic junction box is in and I'll sleep well. The advice and website was also very comforting vindication because in a couple earlier tie-ins that was exactly how I did them.

Thanks to you all.

In thinking some more about this, a 50' coil of 12-2 with ground NM isn't that much. If you have much K&T running through an uninsulated attic, you might save enough on your heating bills to make it worth while to replace it with the NM. GFCI is sensitive to current leakage, and may not work with K&T. Where it runs through an uninsulated wall, it would be fairly easy to use the old single wires to pull through new cable. Once you have modern wiring, then you could add insulation.

... and would do it if for exactly the reason you mentioned... cost savings. K&T certainly lends itself to retrofit wiring far more than the last generation wiring that was secured inside and to the walls with staples. Not easy to tear it out, let alone use it as a guide for the new wiring. The GFCI may not be entirely useless if, for example, the panel is fairly new and has a neutral ground bond pair. Even lacking this, the neutral must have at least some conductivity to earth. It's easy enough to disable or replace the GFCI if it nuisance trips.

Thanks to you all for some sound advice. I will heed it all. There is a bit of distubing news in this though. Long before I bought the house the previous owner had loose blown insulation installed in the attic and it fills every joist space of the attic floor. That means that every run of K&T is immersed in the stuff. I am now unclear about what I should about that since it snakes all over the attic and cutting up the floor and walls is a rough way to find and address it all .

If you have a tip for discerning hot from neutral I would be appreciative. Often the wire colors have all become a matching shade of
Dirty. I have just purchased a 'sniffer' which should now make this process foolproof.

Thanks again for a fantastic service.

All the neutrals should show a low resistance to ground and each other with the power off. Once you have verified one neutral with a water pipe, use it ti identify the others. Those sniffers are great. Do not know how I did without one until picking up one a few years ago.

Perhaps we needed to be specific about snaking new wire in using the old K&T wire as a pull through. Typically the wire goes in a wall through a tube and runs to a box. You could start at the box. Take the old wire loose and bend an eye in the end. Take a length of 12-2 with ground NM, and slit the jacket open about 6 inches. Cut 2 of the wires off plus any paper filler staggering the cuts. Strip about an inch of the third wire, and cut the jacket off at that point. Put the end of the stripped wire through the eye of the old one, and bend it into an eye. Start with the uncut part of the new wire and wind tape around it forming a smooth taper clear past the connected wires. They will make a little bit of a lump, but it need to be smooth as possible and the overlap away from the direction the wire will travel. Now go to the attic or wherever and pull on the old wire. Having somebody to feed the connected wires through the hole in the box is a big help. Do not pull hard enough to pull the wires apart. You should easily be able to pull the new wire up through the hole where the tube was. You can then pull the wire to where it cam out of the wall or ceiling. This time use the old wire to pull the new wire to the box. Secure the new wire to the box using the clamps built into the box. This will also add the safety feature of having the metal box and frame of switches and outlets grounded. Pitch any 2 prong outlets at this time and any 3 prong adapters. If the adapter was not screwed to a grounded box, you were defeating a safety feature.

We have a ca 1910 house that still has a lot of knob & tube wiring. Aside from the problems with blown in insulation in the attic that I'll have to deal with now that I've read about all the problems, I have an immediate issue with untangling/replacing the k&t that's come up now that I've opened up an old wall to do some interior alteration. In the framing of a chase that I was/am hoping to replace/shrink, I found 3 tubed wires. Below is my basement, which being unfinished is open and easy to work on; above is the 2nd floor (the house has 3) which still has a lot of what I presume is the original k&t wiring. Now that this chase is open, and to be able to tear out the framing and put in something new and smaller, and just because I figure the house will last longer than even the most pristine 95 year old k&t, I should replace it. The biggest problem I have, since the wires are separate and all look alike, is knowing what's what. I'm afraid I don't understand the preceding post; anyone have a way to explain this to someone with even less technical knowledge?

The wife wants me to hurry and finish this, and I can't afford an electrician, so any tips would be greatly appreciated.direct email replies welcome. thanks!

... you not understand?

Caution: That there are 3 wires in a group may signal the presence of 220VAC and while you don't have all the feedback you need to proceed with the project, you now know to be ultra careful before you do anything.

One part of the last thread requires a meter that measures resistance so the neutral wires could be identified and segregated from the hot wires. Is this helping? (Would do the direct e-mail but it is easier to use the forum).

I never thought of this being a 220 bunch; one part of me was thinking that the negative runs up somewhere else and these are three positives, or that there's a fourth that I just can't see for all the pipes running up the chase too. (the chase is triangular, two of the wires run up one side, and the third is on another entirely, doesn't seem like they're together, but I could certainly be wrong. I can trace them to the basement I think and see if that's instructive). I'll get home from work and take a much more careful look and see how many wires really run up there. No, I don't understand about resistance and how first to determine the resistance level, and then what that tells me about whether I'm dealing with a positive or negative wire. I'm fine when it comes to running nice new wire and wiring breakers, plugs, whatever, I did a house and it even passed inspection, but the technicalities get beyond me. If it's not too much trouble, can you translate? Thanks again very much.

…to as negative is probably the neutral wire; the one with white insulation used in 'modern' wiring. The neutral wire; as the name implies, is common to all circuits (some exceptions apply with 220VAC) and is never wired to be switched or as the switched wire in a switched outlet. The hot wire is always switched and for this reason the neutral wires can more readily be identified from one circuit to another since they are continuous (not switched), common to each circuit and therefore will have the least resistance from one circuit (pair of wires) to another. On the other hand, since the hot(s) are switched, it is more likely to find some larger than zero resistance between a hot wire and a neutral or another hot wire because the switch and/or load (light bulb, for example) will contribute to the greater than zero resistance. Measuring the resistance from wire to wire can be tedious and sometimes confusing but the important thing is to only measure resistance when the wires or circuits to be measured are dead (breaker set to off). The simplest form of an ohmmeter (instrument that measures resistance) is a continuity tester that either lights or buzzes (or does both) when a near zero resistance circuit (such as 2 neutral wires from 2 separate circuits) is probed. This same tester is louder or brighter when the continuity is the greatest (resistance is the least) and this allows one to identify a pair of neutral wires and thus begins the task of sorting out the hots from the neutrals, etc. Remember, the neutrals are never switched (although they may be present in a box containing a switch) and the hots are. The hots are always dangerous and unless power is totally removed, the neutrals should also be duly respected.

It seems nothing is ever wired up so it is easy to figure out. Add revisions, repairs, and modifications to meet new needs and who knows what you have. Look at the loads those wires are supplying, 220 circuits usually are used with hot water heaters, dryers, ranges, and other high usage appliances. Lights and outlets are usually 110. There is also the possibility more than one hot wire feeding back to the same neutral. I think that is a bad idea, but met code at one time and is allowed to stay in use like K&T.

Can you trace the wires back to the fuse or breaker box? Likely that is the surest way of identifying hot and neutral if you don't have a voltage sensor. For $15 you can pick up a little gadget that the tip glows red when you touch the insulation of a hot wire. Likely when the K&T was installed they didn't follow the conventions of connecting the neutral to the silver terminal or longer slot in the outlet or the outside of the light socket.