New wiring into old K&T outlet and switch boxes

[Mark G.]

Good morning.

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?

Thanks

-Mark

[Mark G.]

Good morning.

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?

Thanks

-Mark

[Steve Barker DLT]

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

s

[Mark G.]

"Steve Barker DLT" wrote: news:zsudnXn9GrSAio_UnZ2dnUVZ [e-mail]...

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

[HerHusband]

Mark,

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

[Wayne Whitney]

You can usually replace an older box with a modern "old work" box without tearing into the wall. The hard part is getting the old box out, sometimes you have to dismantle/demolish it in place and pull out the pieces. Then you may need to enlarge the hole slight for the replacement "old work" box. Be sure to watch your box fill.

BTW, if you are considering extending an existing k&t circuit with romex, don't do it. Run your new romex branch circuit back to the electrical panel. An undisturbed k&t branch circuit will often continue to work OK, but adding modern loads to it will only cause problems.

Cheers, Wayne

[John Grabowski]

I would evaluate each situation to determine the best course of action. First of all I would definitely not tie into an existing K & T system. You would just be asking for trouble. I'm assuming that you have one of those old black painted electrical boxes installed now. Sometimes they have provisions for cable clamps which I can muster from my truck. It would be necessary to drill and tap a 10/32 hole for a ground screw and scrape the paint a little for good ground contact. Unfortunately the black boxes also tend to not have the cubic inches needed for multiple conductors. In some cases they are installed in wood lathe and plaster walls which can be a mess to swap out from a wall that is finished. However if the wall is going to be repaired and refinished I would change out the box. Sometimes the boxes are a little loose already and some gentle prying will free it completely.

Can you post some pictures?

[Mark G.]

Here is what the beasts look like:

[Steve Barker DLT]

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

[Bobk207]

Box fill can be a problem. The old K&T switch boxes are not even rectangular and really don't have much room.

I've replaced more than a few of those boxes without destroying the wall locally. It's a bitch but doable with a die grinder or a Dremel (with fiber cutting wheels) or a Roto-Zip but imo worth the effort to not damage & require repair of the finished wall. With a little practice you can actually do it and have the work easily be covered by the switch plate.

One problem in my old house is often the boxes were set too close to doors and the door molding eclipses part of the box...I guess in 1930 electricity was kinda new and the electricians didn't allow enough room for the trim, so I've had to move over about 1" (remove & replace, actually) about 1/2 of the switch boxes (about 10) .

then I just use as deep a tiger box I can find or I back screw mount & SIKA epoxy bond a standard new work switch box (single gang) usually again a DEEP one..... the fill capacity of a standard cross section and deep box is much better than a tiger box, plus GFI's and dimmers fix better.

I've removed almost all of the K&T from my 1930 house and I'm still at a loss as to why some guys are SO afraid of the stuff.

In every run I've removed the insulation has been soft and slick and compliant ....even the stuff in the attic. Only in the switch boxes (and the occasional ceiling light box) at the stripped ends have I observed any insulation deterioration and this was only the last inch or so........easily fixed with a few inches of heat shrink tubing when necessary. IMO good to go for another 20 years at least. The copper conductors appear to be tin plated as well.

A 20 amp breaker feeding 12 gage wire should be just fine to add onto, not that I've done it...my house is now nearly all EMT or flex with 12 gage THHN/THWN stranded.......but why the concern about K&T ?

I've seen houses from the 50's where the first generation (?) Romex (black sheathed paired black & white with ground) is in much worse shape than my nearly 80 year old K&T.

cheers Bob

Nice floor tile.....anyone know where to get stuff like it today?

[John Grabowski]

Obviously those will not pry out as easily as I originally thought. Some damage may have to be inflicted to the wall. As someone else suggested, careful cutting with a Dremel or Rotozip will make a cleaner opening. Because of the bevel back corners those boxes don't have the cubic inch capacity needed for multiple conductors and a device.

[HerHusband]

Bob,

I rewired my in-laws house last year, and my experience was completely opposite of yours. They have a 100 year old house, though I don't know how long the K&T wiring has been in the house. It seemed to be a later addition, followed by several "updates" over the years. A real show case for the various electrical technologies of the past several decades. :)

With very few exceptions, the insulation was dry and brittle, with many wires being completely uninsulated and exposed. It was a miracle the house didn't burn down from all the burnt and corroded terminals, or that someone didn't get electrocuted from the uncovered bare wires in the basement.

Even the "newer" cloth covered cables were in really bad shape, though the rubber insulation on the individual wires seemed to be mostly in good shape.

The rusted fusebox with the exposed main knife cutoff switch looked like some kind of ancient torture device. Rust, burnt terminals, broken insulators, etc. Scary! :)

Anthony

[Bill]

I second the RotoZip. I just helped someone cut A/C vents in really old plaster with lath. Cut 9 vents, but went through as many bits. The RotoZip did a great job. It even has an attachment for a vacuum.