[mikestorm]

Due to a leak that originated above the living room of the house I just bought (built in 1920), I decided to pull down my very old ceiling and have new drywall and molding hung.

Doing so revealed two things.

1) One of the previous owners painted over the wallpaper :rolleyes:

2) My house is lousy with knob and tube wiring (given the age of the house I guess I shouldn't be surprised).



If this stuff is live, it would explain the existence of at least one older-looking two prong outlet per room. Should I be concerned? Is there an easy way for me to check to see if this wiring is active?

[labman]

I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit.

As I understand it, left alone, knob and tube still meets code. I think there is a limit to how much repair work you can do before you do have to rip it out. I certainly don't think you can come back and add a ground wire leaving you with the 2 prong outlets. I would be suspicious of any 3 prong ones you have. If they were later work and mounted in a metal box fed through metal flex or conduit, they should be grounded OK. One of the other problems with knob and tube is that you aren't supposed to bury it in insulation.

[jamlove]

Labman is right; any wiring that met code at some point in history, by "backward compatibility" (to use a programmer term), meets code today. Provided you aren't altering it.

Once you are going to rewire something though, you can't leave it there. You can't add on or modify it, you have to remove it and run new wire. This is according to my electrical inspector... when I ran new wires, he told me I was not even supposed to leave the cloth-insulated wire in the walls at all, even though it was no longer connected! (it's possible that was just his preference, but it does make sense to avoid any future confusion)

Anyway, you'll be surprised how tough this stuff is to get out! I am amazed at the work that went into older homes.

My own decision was to remove all of it - every knob and wire, and run all brand new stuff. Mostly this is because, after 95 years, my house had a real hodgepodge of new combined with old, over many generations of materials, and I didn't like it. I had aluminum mixed with copper, 2 and 3 prong outlets, lots of junction boxes, etc. I did not consider it safe.

HOWEVER! THere's a lot to be said for the "if it ain't broke don't fix it" argument! It's a LOT of work to rewire a house. Very expensive. My things to consider would be:

1. are you running lots of appliances/items all the time
2. are you running lots of GROUNDED appliances, using 2-to-3 prong adapters a lot
3. do you have enough outlets
4. are your 3-prong (newer) outlets properly wired/grounded (you'll need to check, like Labman said)
5. are you wanting to install any insulation in these walls

etc.

When I considered these things, I decided it was worth the work. My old house had ONE OUTLET per room! That's a little tough to live on in today's world... and dangerous, if you want to run multiple appliances.

Then again, I have a degree in Electrical Engineering, so I knew I could do it myself :) Don't forget to weigh the cost of having an electrician tackle this... it can be hefty.

Labman's voltage detector tool sounds great, I got to get one!

Best of luck,

James

[mikestorm]

1. are you running lots of appliances/items all the time
2. are you running lots of GROUNDED appliances, using 2-to-3 prong adapters a lot
3. do you have enough outlets
4. are your 3-prong (newer) outlets properly wired/grounded (you'll need to check, like Labman said)
5. are you wanting to install any insulation in these walls

1. Yes (but only via properly grounded outlets)
2. Only in the kitchen (fridge). All other outlets are new and properly grounded.
3. Yes. It seems the house was completely rewired, so not only do I have a sufficient amount of grounded outlets in each room, I have one or two legacy outlets which, aside from the occasional desk lamp, I don't use.
4. Yes. Home inspector checked every single three prong he could get at in each room.
5. No, the house is insulated very well. The ceiling was pulled down for two reasons. First, there was water damage. Secondly, I hate ceiling panels (I think they're tacky if they are in what is supposed to be the "showcase" room of the house.)

[jamlove]

Cool, cool. Well, sounds like you had the house properly rewired in the past, and they just were not able to remove all the knob n tube. Without pulling walls and ceilings down, this makes total sense. So, provided those wires aren't energized, you could just leave them there.

If they are carrying current, but not acting as the main supply for the upstairs or something, they'll be fine I would think.

Only if they were the main supply lines to rooms or something, would I think of replacing them... but sounds like you had a good update done.

Good luck, j.