New wiring into old K&T outlet and switch boxes

Posted by Steve Barker DLT on November 6, 2008, 10:18 pm

I'd bet they just run the wire into them and keep going.... Why not ask a
few? If you can actually find an electrician that re-does old houses.

s

>> Just run it in there and be done. don't ask, don't tell.

> So what does a professional electrician do with the old electrical boxes
> when replacing k&t with romex? Does he run the romex into the old
> boxes? Does he tear into the wall and replace the old boxes with
> modern boxes? Something else entirely?
> Thanks
> -Mark
>

Posted by HerHusband on November 6, 2008, 2:00 pm

Mark,

> Is it feasible (and does code allow) me to run romex into an existing
> metal outlet or switch box designed for knob-and-tube wiring? Or do I
> need to install new boxes to replace the original boxes?

I rewired my in-laws house that had knob and tube wiring, and I don't
recall the original fixtures even having boxes. For ceiling fixtures the
wires came down through tubes and connected right in the light base
itself. The original lights had pull strings instead of switches. The
wall outlets were just screwed to a hole in the wall, no box at all!

At some point the system was "upgraded" to add wall switches for the
lights. They used cloth covered cable like romex, and metal boxes.

I obviously had to add new boxes for the lights and outlets that didn't
have any to start with.

I was able to reuse a few of the metal boxes for some of the wall
switches. I removed the cable clamp, used the old cable to pull the new
wire through, then remounted the cable clamp. I did have to add a
grounding pigtail to the box.

For wall outlets, the metal boxes were usually too small for today's
grounding outlets. By the time I added the grounding pigtail and the
wirenuts for the new ground connections, the boxes were just too cramped.
So, I ended up replacing the boxes for the outlets.

I also replaced several of the wall switch boxes to add another gang, to
support a larger switch (i.e. dimmer), or when I had more wires coming
into the box.

In my case, the boxes were fastened with bent metal tabs that made them
fairly easy to remove. Depending on the situation, I used both "remodel"
style plastic boxes (with the tabs that flip out), or screwed plastic box
tabs into the lath. I even installed a few metal boxes in tight locations
where I couldn't find a plastic box that was suitable (i.e. where two
light switches were back to back in a wall).

Long story short, as long as the box is secure, has a way to secure the
cable, and is either plastic or can be grounded, and has enough room
inside, they should be reusable. But many times it's just easier to
replace.

Anthony

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