Rewiring knob & tube

Reply

  #1  
Old 12-22-14, 03:12 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
Rewiring knob & tube

I'm going to pull a permit this week to remove the last bit of knob&tube wiring in our house.

Right now I have two 20A circuits feeding it, the switches on the two breakers are joined with a plastic clip so they operate as one.

One circuit feeds
- bathroom (knob and tube; one overhead light, one wall light and one GFCI outlet)
- hallway (knob and tube; one wall sconce)
- two bedrooms (knob and tube; one overhead light fixture in each room).

The other circuit feeds
- kitchen (romex)
- dining room (knob and tube; one outlet, one overhead light)
- living room (knob and tube; one outlet, two wall sconces, one exterior light outside front door plus I think a ceiling fixture that has been abandoned and plastered over)

I'll be wiring as three circuits:
1 20A circuit for bathroom. GFCI, overhead light, wall light, add Panasonic extraction fan
1 15A circuit for kitchen lights, connecting to existing romex
1 15A circuit for 2 bedrooms (2 lights one per room), hallway (1 wall sconce), dining room (1 light), living room (2 wall sconces) and one exterior light. [Outlets will be moved to a different existing circuit that already partially feeds the rooms]

The only question I have is on the wall sconces. The exterior wall behind the sconces in the living room is filled with blown in cellulose and even if I installed a T junction box in the attic above each and just ran a single wire down to each, I think I'm going to have a hard time getting that into the old circular cast-iron box and because of the knobs I doubt I could use the old wire to pull new. I doubt it's code to reuse the existing box anyhow.

Which brings me to problem 2. I bought another sconce off eBay for the hallway (to match the originals in the living room). The problem is that the sconces are narrow and don't fully cover a modern box. I don't believe it's code to bury the box but maybe there is a solution I'm not considering?









 
Sponsored Links
  #2  
Old 12-22-14, 03:52 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
The only thing that my local electric house had in a narrow(er) width was this which isn't going to work (mounting wise). I'm sure there is a minimum code volume for the box also.

Product Datasheet -- 640

 
  #3  
Old 12-22-14, 05:11 PM
Member
Join Date: Jun 2012
Location: USA
Posts: 1,024
  #4  
Old 12-22-14, 05:22 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
The blue box in my pictures is 3 1-2" tall (excluding the mounting tabs) by 2 1-4" wide. and that is too wide.

What are you supposed to do when mounting a legacy fitting like this?
 
  #5  
Old 12-23-14, 10:57 AM
Member
Join Date: Jun 2012
Location: USA
Posts: 1,024
Even the old one was mounted improperly. It looks like it was a 3 1/2 box with center fixture stud but they plastered over the edges to hide the size.

You could take that smaller Raco 640 box and add a fixture stud instead of the strap. The box volume is 7 inches so to be legal you would need to feed it with AC cable (2 wires, sheath is ground).
 
  #6  
Old 12-23-14, 11:30 AM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
The old box (pictured) is from probably 1920 when the house was built. It's cast metal. But yes it's definitely plastered over. I expect "code" was different back then. Or maybe the sconces were added later but they are definitely old.

I'd not heard of the term fixture stud, I just googled. How would you recommend adding a fixture stud? I expect the metal back of the Raco box is too thin to tap a thread into so I'd have to add some kind of female adapter such as this:



If there is a better product you'd recommend, please let me know.

Thanks for the suggestion on AC cable. I'll run romex in the attic then and place a junction box above each sconce and run a single length of AC down from the junction box to the Raco 640 with the fixture stud.
 
  #7  
Old 01-16-15, 09:45 AM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
I finished all of the wiring. Just fixing all of the lathe&plaster damage now.

I managed to reuse the two existing sconce boxes. I noticed they each had an upper knock out for a standard romex clamp and I was able to find 9/16" plastic plugs (red arrow) to fill the side knockouts that had been used for the old cloth covered wire. City inspector said it was fine to reuse the box as long as I used an approved clamp.

One issue; I'm not sure what the best way is to ground these boxes. There is a nut (blue arrow) visible which presumable holds the box halves together.

I managed to find a handybox that was 2" wide the exactly covered the sconce base for the new installation. I used a ground clip for the box but I could have just as easily used the screw location on the bar. The aluminum body of the sconce in theory is grounded via the threaded rod and the nut but I'm thinking of adding a direct ground to it, attach to the screw that mounts the bulb holder using a spade terminal or similar. Comments?







 
  #8  
Old 01-16-15, 10:25 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,587
Either a ground clip or a screw into a 10-32 tapped hole would work.
 
  #9  
Old 01-16-15, 11:04 AM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 161
I can't see where a ground clip could attach. The edge of the box has an odd lip. I can drill and tap a hole (though I only have metric taps, I'll have to buy an imperial set). This seems better than trying to use one of the mounting holes.
 
  #10  
Old 01-16-15, 11:15 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,046
You can get self tapping ground screws.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes