Help: "Knob & Tube" Wiring Problem!

[Dougster]

Hope this post is appropriate for here...

My GF lives in an old 2-family house which still has a small handful of the original "Knob & Tube" electrical circuits still in operation. One of those old circuits feeds her dining room chandelier through a wall switch. Recently, the wall switch stopped working and I was given the assignment of making it work again. But when I opened up the switch's single switch electrical box to replace the switch, I found that a previous repair had been made to lengthen one of the two wires going to the switch with a tiny gauge pigtail and small wire nut. Apparently one of the original two K&T leads going to the box had broken off way toward the back of the box... barely visible now.

The pigtail and wire nut that were used for the repair umpteen years ago is nowhere near adequate for the modern chandelier's current draw. It's amazing there was never a fire. But now the task has fallen to me to lengthen the broken wire in some sane, safe and sensible way. It is far too brittle to try pulling more length out from between the walls... and much too short to get a decent size pigtail and wire nut onto it. Other than maybe soldering and shrink tubing it... does anyone out there know of a safe way to "lengthen" that old, short and very brittle K&T line???

Dougster

 

[kennyd]

My best advice is to learn how to "fish" the walls and replace that wiring. If your not up for the task...hire an electrician. It will be cheap in the long run

 

[JPCjr]

There really is no GOOD way to fix what you've described other than re-running the whole wire. If you're lucky, you can attach the new wire to the old wire and use the old wire to pull the new one through the wall.

If re-running the wire seemed like a major project, I might try to use an underground splice kit. You can get them with butt splices that have set screws, and that might allow you to attach a pigtail to the short wire. The splice kits usually come with adhesive lined heat shrink tubing that protect the splice.

I would not try soldering, as it will not make a suitable electrical connection.

 

[Dougster]

My best advice is to learn how to "fish" the walls and replace that wiring. If your not up for the task...hire an electrician. It will be cheap in the long run

It was actually an electrician that made the decision to leave certain of these circuits K&T when the whole place was 95% rewired. Everything he could reasonably replace, he did. This is one of those he couldn't... presumably because of the light circuit extending up into the first floor ceiling (and God only knows where else!!!).

Of course, I could shoot him today for not trying harder... but that is another story!

Dougster

 

[Dougster]

There really is no GOOD way to fix what you've described other than re-running the whole wire. If you're lucky, you can attach the new wire to the old wire and use the old wire to pull the new one through the wall.

If re-running the wire seemed like a major project, I might try to use an underground splice kit. You can get them with butt splices that have set screws, and that might allow you to attach a pigtail to the short wire. The splice kits usually come with adhesive lined heat shrink tubing that protect the splice.

I would not try soldering, as it will not make a suitable electrical connection.

Underground repair kit is a good idea if they make them that small in gauge... worth looking into.

I never knew this before yesterday, but K&T circuits are ALREADY soldered all over the place. It's part of how they built them. Go figure!

Dougster

 

[Inspector507]

Dougster,
Go here and look for a W30 connector it's on page 4 or 5. If you can get a pair of needle nose on the wire, just slip this on and extend from there. You can also use a P-Nut, do a google search.

 

[Dougster]

Dougster,
Go here and look for a W30 connector it's on page 4 or 5. If you can get a pair of needle nose on the wire, just slip this on and extend from there. You can also use a P-Nut, do a google search.

Excellent solutions Inspector507!!! Thank you!!!

Dougster

 

[JoeL4330]

move the box a few inches?

 

[Dougster]

move the box a few inches?

Believe it or not, this K&T wiring comes in from the basement and goes up and over the dining room doorway before splitting and going up to the chandelier and down to the light switch. The switch box would have to be moved upward to gain a little slack... not a pretty or practical solution.

I think Inspector507 has my solution... essentially a high amperage, solid copper wire crimp or push-on connector. If I can find one or the other at the local electrical supply house, it would be ideal!

Dougster

 

[MossRoad]

You are taking the easy way out!

This project clearly calls for sledge hammer, saws all, trash cans full of plaster and lathe strips, brooms, dust pans, plaster's stilts, etc... where's Tim Taylor when you need him???

 

[Soundguy]

I would not try soldering, as it will not make a suitable electrical connection.

Soldering makes great electrical connections.. it does however make lousy mechanical connections.

Ever notice they stopped using wire wrap posts on circuit boards and went to solder connections? It wasn't because solder didn't make suitable electrical connections...

Soundguy

 

[Dougster]

You are taking the easy way out! This project clearly calls for sledge hammer, saws all, trash cans full of plaster and lathe strips, brooms, dust pans, plaster's stilts, etc... where's Tim Taylor when you need him???

The GF is watching me like a hawk on this. One smudge on the wall and I am in the doghouse for a month. Smash apart the walls and I am a dead man!

Dougster

 

[schmism]

Plaster walls?

id extract the old box out of the wall and replace it with with a new work box. this would give you a hole in the wall large enough to access some of the wire in the wall.

with a slightly larger box you can still ensure that the "splice" is in a box and not in the naked wall....

 

[MossRoad]

The GF is watching me like a hawk on this. One smudge on the wall and I am in the doghouse for a month. Smash apart the walls and I am a dead man!

Dougster

Good thing you have the will to live! Seems everyone has a story about the first time they tried to cut into plaster with a saws all only to have the lathe strip vibrate out and rip a 3' strip vertically away from the cut.

 

[schmism]

Good thing you have the will to live! Seems everyone has a story about the first time they tried to cut into plaster with a saws all only to have the lathe strip vibrate out and rip a 3' strip vertically away from the cut.

ah thats why you use diamond wheel on a 4.5" angle grinder.... makes a mess but slices through the hard plaster like butter with no vibration to disturb surronding plaster/lath

 

[Dougster]

Plaster walls? id extract the old box out of the wall and replace it with with a new work box. this would give you a hole in the wall large enough to access some of the wire in the wall. with a slightly larger box you can still ensure that the "splice" is in a box and not in the naked wall....

I think I'm okay in that latter regard... but yes, removal of the old box and replacement with a nice new plastic switch box would have been a last ditch option to possibly gain a bit more working length on that short wire. However, I remain fearful of breaking off the wire even further back if I mess with it too much. It is unclear exactly where the wiring makes the transition from true K&T to those heavily insulated "pigtails" for switch box connection purposes. If very close to the switch box, the consequences of box removal could be ugly.

Dougster

 

[Dougster]

ah thats why you use diamond wheel on a 4.5" angle grinder.... makes a mess but slices through the hard plaster like butter with no vibration to disturb surronding plaster/lath

Another "this old house" issue... I'm guessing there is asbestos mixed in as part of the crumbling wall plaster "brew"...

Dougster

 

[JPCjr]

Soldering makes great electrical connections.. it does however make lousy mechanical connections.

Ever notice they stopped using wire wrap posts on circuit boards and went to solder connections? It wasn't because solder didn't make suitable electrical connections...

Soundguy

Ok, fair enough. I should have said "I wouldn't trying soldering because I don't think you'll be able to make a suitable electrical connection given the conditions you described"

Soldering makes a good electrical connection (I still won't say great...I'll reserve that word for welding or ultrasonic bonding) if the oxide layer is completely removed from the workpiece, the workpiece reaches the proper temperature without allowing a new oxide layer to form, the solder is properly applied, any flux is completely removed from the connection after the solder is applied, and there is proper stress relief on the connection. This is not difficult in PCB populating, but it is in the back of a single gang box with a several decade old wire that is very oxidized and barely visable.

 

[Dougster]

This is not difficult in PCB populating, but it is in the back of a single gang box with a several decade old wire that is very oxidized and barely visable.

Make that at least 70-80 years old... and not exactly "in my face" for close-up work... but still highly doable if it proves necessary. It actually shocked me how well the ancient copper wiring had held up. It was hardly oxidized as all and reasonably supple to my surprise... making it a real mystery by whose hand and how it had broken off so far back in the box many years ago.

Dougster

 

[Soundguy]

Good soldering takes technique and skill.. no doubt there. Once you get the stuff to tin.. you got it by the tail...

Soundguy

Ok, fair enough. I should have said "I wouldn't trying soldering because I don't think you'll be able to make a suitable electrical connection given the conditions you described"

Soldering makes a good electrical connection (I still won't say great...I'll reserve that word for welding or ultrasonic bonding) if the oxide layer is completely removed from the workpiece, the workpiece reaches the proper temperature without allowing a new oxide layer to form, the solder is properly applied, any flux is completely removed from the connection after the solder is applied, and there is proper stress relief on the connection. This is not difficult in PCB populating, but it is in the back of a single gang box with a several decade old wire that is very oxidized and barely visable.