Locating and removing Knob and Tube
So, we ‘re trying to get two floors of the 4 floor remodel set up for an Icynene foam insulation install; very exciting stuff.
Made more exciting by the presence in the house of knob and tube wiring. Can’t foam around it; code says it would get too hot and represent a fire risk.
Everywhere possible, the old knob and tube is getting removed; but in order to find it and get rid of it where it’s still in the plaster lath walls that are still up (if it’s even in there), I would like a more elegant solution than tearing all of the plaster off of every wall in sight, only to find there was nothing there.
Any ideas on how to scan the floors and walls that are deeper than 4 inches? Something that can find live circuits so we know where to go?
Some of the commercial made sensors (using inductive technology) can pick up the alternating current as deep as about 4-6 inches; but what about stuff that’s deeper?
Anybody have a non-invasive technology answer?
Thanks
NotaClue
PS
At this point, you are wondering “hey, why not just turn off the circuits and run new ones?”; this very question was asked at the jobsite and the foreman seemed to become agitated; reasoning is unclear; Some of the circuits on the top floor are apparently offshoots of still-live ground floor and in-law apartment circuits that are not getting done on this pass…
Or so it seems.
Replies
The forman is agitated because he knows that it's really the right thing to do but it going to cost $$ and he has a budget to stick to. Been there. Knob & tube is a PITA and a crapshoot if you're doing renovation because you don't know where things go. They may have borrowed a neutral or hot from some other circuit that may be jumped over from who knows where...and you mentioned a one time mil apartment, so who knows what tampering was done. Also there's no ground. There was probably some method to their madness back then but it has been lost through the update of products and tampering.
I don't see where there's any question. We're talking about fire here, homes and lives. Explain to the homewoners, then go to the service panel and snip away. Run new.
To answer your question though, I don't see any other way than to rip into the plaster to find out about the k&t, and once you've done that it's open for new.
Actually, if a sensor will pick up a regular romax at 6" it will do K&T at 8 or 10. The ground/neutral in regular romax tend to shield the hot from sensors, but with K&T the wires are conveniently separated. The trick is to find a decent sensor.
Beyond that, simply account for all the wires in the house. A little difficult, but not that bad. Open up all outlets and light fixtures, see what kind of wires are there and where they're headed. Check from attic and basement to see what wires are heading into the walls. You should be able to identify the approximate location of 90-95% of the wires.
Nota,
I don't know where you would find one, but they do make sensors that will find deep wires. They require that you disconnect the circuit at one end and hook up a "transmitter" that sends a small signal through the wire. Then the reciever can find it. They use them for finding buried cable and pipe, so I am sure a 6" wall would not be a problem. Maybe try a local electrical supply house ?
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Try a cheap AM pocket radio tuned off station like around 600 kkz to find hot wires. Probably you have one already.
your junction boxes will probably come out of walls and ceiling without dammage. i replaces 2 k&t runs in my house and only had 1 hole to plaster but there is alot of wire in various walls that will always be there. it not hot so i dont have to worry.
it seemed to me that the jacketed wire must have been more expensive since the k&T went out of the way to make jacketed runs shorter. the basic methedology seemed to be there were 2 circuits for the house. k&t went north along one long wall and south along the other then up the wall to the next floor. lights had power to them instead of the switch. every thing was in the ceiling for that floor and dropped to the switches/outlets. but thats just one house in wisconsin.
after it was updated the lights in the house were brighter. scarry.
take the stuff out while you can even if you have to eliminate upgrade to do it. once you dig into it youll wonder y it was ever done this way.
if you find someone with even nominal experience to help you wont have alot of plaster to do. use your stud finder too to tell you if your run is going parralell to the joist bay or perpendicular
Alright, you guys have me convinced; it's all coming out now...
Now, just gotta make that all make fiscal sense...(and work through the foreman's fear of somehow burying a circuit that got missed in layer of foam and leaving a thermal time bomb ticking)
NotaClue
Edited 3/26/2005 3:22 pm ET by NotaClue
Why find the old wires? Rewire the house and abandon the knob and tube. What am I missing here?
Nothing much; finding the old wires is about handling the foreman's neurosis...
NotaClue
Are you allowed to just leave dead old wires buried in the wall? Everyone does it of course, just have this niggling feeling that code is a PITA on this issue. Or maybe I'm the PITA.
Technically, you are required by the NEC to remove unused systems whatever thier voltage or purpose. However, the codes allows the Authority Having Jurisdiction(the inspector for whoever adopted the NEC in your area to make the call.
I recommend that if you abandon any old circuit anywhere, make sure that both ends of every cable or wire are either in a box or out of a box. You don't want to risk that someone inthe future energizes the circuit you abandoned. Marking the abandoned circuits as such would be a good idea too.
Could you provide a section for the requirement to remove unused systems?
I might have miss spoke. I do know that is code in my jusidiction. It may be in the city code or the state code. I couldn't find it in the NEC today, but I don't have my fast finder at home. I'll keep looking though.
I still think that its good practice when possible.
Your right.Rewire. Complete and total. Better find a contractor that does it a lot as tracking and replacing K&T installations in old houses is an art form. Expect the price to be twice, if not three times, what a wire job on new construction would run for a similar house. But trust me they will earn every dime. It is frustrating, dirty and demanding work.Ask about removing baseboards, trims around windows and doors, and maybe installing chair rails to speed things. An experienced 'old work' contractor, look for rude and crusty guys that talk to themselves and have a perpetual look like they smell something bad, will have a large bag of tricks.K&T can stay in the walls as long as it is completely disconnected and situated so it will never be reconnected. Code, but bowing to the AHJ is they have a different standard, doesn't demand otherwise.
There are tools available for locating wires, although the prices aren't necessarily low. Harris makes some of them, and at least one is for deep scans. Just used one this past week and it really helped, but we had some of the wires located with the lower sensitivity model. You could find then with google and your local Grainger or other electrical supplier should have them.
You already got some great advice. The electrician we use (who is a genius) will not as a general rule try to kill k/t circuits as Jer said cuz you dont know where there are soldered splices that feed all sorts of other circuits.
Suck it up and rewire with Romex. Hey, it's only money! Now the payback for the icynene is pushed a bit more into the future I guess :)
How's the window saga?
Yah; we're going to use one of those induction signal tracers to find all the wires; pretty cool stuff.
The Window saga has begun!
Window sub seems to know his stuff; even convinced the skeptical foreman.
We'll see if he can really execute on his promises.
I'll post pictures as they go back up again.
NotaClue
If you pull out an outlet or switch to check the wiring, I'd be careful assuming that just because you see modern romex that it's not connected to K&B somewhere. I'm rewiring several old K&B circuits in my 1865 Victorian and found that a previous owner had spliced in 3 or 4 feet of 14/2 wire and just wire nutted the thing to the old K&B -- inside the walls -- no boxes or tape just a nice flying splice! Needless to say, it's all being rerun to code. Be sure to check each end of the circuit and if there's any doubt just run a new line. Wire is cheap compared to the risk of missing something like that. You'll sleep better too....
yep; that's good advice; there are crazy circuits in the house already; for example, from a previous life as apartments, it has 4 panels, in theory, with one for each floor. In practice, the top floor's pantry is being driven from the basement's panel----so concern about how this came to be is general and broad.
NotaClue
Don't mean to belabour, you've already said "it goes".
FYI, with enormous patience, you can also 'map' K&T circuits visually. Knock out one hot or one neutral at a time to help identify plausible runs. Then trips to attic, basement, test holes and judicious use of dental mirrors and flashlights can confirm it (power out) This permitted us to plan a complete rewire in chunks and keep the house cosmetically acceptable throughout. You could minimize the number of wall/ceiling sections to knock out and replace.
If most of the K&T circuits are unaltered (such as to bedrooms that haven't be reconfigured) the runs may be quite predictable to renovators with local knowledge. There were usually a minimum number of vertical runs and then runs along joists - for example, you'll see bedroom plugs at 180 degrees across a bedroom using a joist space which is the same or adjacent to where there is a ceiling fixture below.
BUT, it's not the original wiring that will bother you, it is the generations of hacks in between, that did the lashing and bodging. So here's the tip. Be just as suspicious of anything leaving the panel as Romex. Insist on laying eyes on it from origin to end, too.
I agree; the problem isn't the originals; it's the hacks.
Thus, the Tempo Progessive Tracker II, designed to hunt down cables, wires and pipes.
We hope.
NotaClue
We're in the process of rewiring a 1920's brick home with knob and tube, and we've come along alot of metal sheathing that goes back into the knob and tube, so don't believe the whole line is armored cable.
We've also found that most of the lights are charged from the light to the switch, which is bizzar. Even with the switch disconnected the light is charged.
Knob and tube is also unique that it is kind of like a tree root, that it'll shoot off in a direction and keep expanding from there, but there is a main line. Trick is finding that line and cutting it back bit by bit. In our house, it ran around the ground floor outlet from the basement, then upto the attic and dropped down for all the second floor lights and outlets. What got us, was that the ground floor overhead lights and switches came off the line from the attic.
It's a trick for sure, alot of checking as previously recommended.