Help: "Knob & Tube" Wiring Problem!

[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.