Old house with old knob & tubbing wiring

[Robert Mattison]

Many reading this know about my other thread. I started this one as it is
related to another subject matter.

In the attic of a very old house, found K & T underneath floorboars with
insulation over it. I tested with one of those non-contact voltage checker
which went off, with sound & light indication the present of AC voltage. I did not check it out with a analog meter.


Want to be very careful, before I say anything, looking for feedback on
this subject. Thanks to all that reply to this thread.

[Alton Darty]

Report what you found. K&T with insulation covering the wiring is a concern that needs to be brought to the attention of your client. While K&T itself is not always bad, we have to look at what has been done to the material. Splices not in j boxes, improper connections and insulation over the wires are issues that can lead to serious problems.

[Bill Kriegh]

Report what you found. K&T with insulation covering the wiring is a concern that needs to be brought to the attention of your client. While K&T itself is not always bad, we have to look at what has been done to the material. Splices not in j boxes, improper connections and insulation over the wires are issues that can lead to serious problems.


It was a common and accepted practice to make K&T splices that weren't in J-boxes. There were, of course, rules on how this was to be done. And, specifically forbidden is a splice where wires were joined end to end with no close support of both wires. Tap splices were generally done next to a knob. A soldered splice, generally covered with rubber tape then friction tape, done in the open, was the norm.

If you are going to comment on K&T, other than it exists, some reading is in order. (there is still a NEC section on it that covers a small bit ) I've seen K&T wiring my grandfather did that is in better shape than much more recent jobs by others. Of course, some of it isn't due to a variety of things, and that is the general problem with the stuff. Unfortunately, anything with fabric covered rubber is going to be suspect.

The wire typically used in K&T installations is not rated to be surrounded by insulation, and most of it by now has become brittle so that any movement caused by the insulating process will cause an insulation failure. Even if you have a well done and intact installation, if you are going to do anything but look at it from a distance replacement needs to be recommended.

[Michael Thomas]

Try to insure a house with energized K&T.

At least here in IL, ain't gonna'' happen.

[Thomas McKay]

Very bad stuff, its the original form of electrification; replacement is always recommended as it is virtually impossible to insure. One of the big issues is that the insulation in most cases has been eaten off by vermin which just leaves live unprotected wiring. additionally the switches which were used during those installations have a high rate of failure. Don't fool with it be very careful in any attic where you see it it can get you! :(

[Scott Patterson]

Report what you found! Report that you found active K&T wiring. Tell your client that this is the original wiring for the home and that it is outdated by today's safety and usage standards.

80 years ago it was state of the art, but now it is really a fire hazard. K&T was never designed to be covered with insulation. As Michael noted, getting homeowners insurance might be an issue.

Do not soft sell K&T wiring.

Did the home have a fuse box or breakers?

[Robert Mattison]

Thanks guy for all your valuable input on K & T. Seller claims he had
all removed. Boy was surprise when I told him.

[James Duffin]

Once K&T is covered in insulation it is pretty much ruint and needs to be decommissioned. I tried to uncover some just as a test to see if it could be done it was not practical to do so.

[Bill Kriegh]

I was hoping the take away from my comments would be don't bother analyzing K&T wiring. Just call it out as questionable and obsolete and be done with it.

[Michael Thomas]

Thanks guy for all your valuable input on K & T. Seller claims he had all removed. Boy was surprise when I told him.

Very common.

IMO if you can see ANY K&T, energized or not, report the possibility that energized K&T my exist elsewhere.

I had an inspection a few years back were about 4 feet of energized K&T, correctly terminated in a box at each end, had been left in place where it passed through a masonry wall to an addition. Everywhere else I could access had been rewired in conduit (as is often required in suburbs near Chicago) - not a trace of other K&T.

I reported what I had seen, along with my standard disclaimer re the possibility of other K&T I could not see, along with the observation that the false grounds at many baseboard outlets could have been wired that way due to the absence of a ground in K&T segments upstream of the new work, and recommended a electrician investigate further.

Buyer remodeled the house, and found that the K&T in the attic had not been replaced when the attic was finished - all the original K&T was still up there, behind the knee walls, attached to the rafters and running down into the walls.

Cost around $4K to correct.

I found about this when I did another inspection for the same client:

"Well, at least you warned me..."

[Nick Ostrowski]

I've talked to electricians who have been on both sides of the fence. Some say it needs to go, some say it is not ideal but can be OK. I see a lot of it.

[Jerry Peck]

A couple of things to keep in mind when you see knob and tube:
- most knob and tube was installed before thermoplastic insulation came along, which means it most likely has rubber insulation, which means it most like (99.999%) needs to be replaced
- knob and tube which reads 'dead' may in fact just be a switched circuit with a switch 'off'
- no knob and tube is allowed to be covered with insulation

Those are just the obvious starters, then there is the fact that any 'modern day' extension of the knob and tube was *likely* done incorrectly and not safely.

When Bill Kriegh said: "I was hoping the take away from my comments would be don't bother analyzing K&T wiring. Just call it out as questionable and obsolete and be done with it.", he was, I believe, stating that the finer points of knob and tube can best be discussed while handling the knobs, tubes, and wiring while dissecting the old wiring and insulation on your work bench, contemplating what was while sipping a cold one (of whatever your preference is). :)

[John Kogel]

Here's some active K&T in the garage of a 1930's house I had last week. Yes, it has been painted for inexplicable reasons. Old folks have lived here for ever, now new folks are moving in. This garage circuit will be easy to replace.
It's the ceiling light fixtures they need to be worried about. In my mind, antique fixture mean active K&T is still up there.

Another point to be aware of in an attic situation is that if the first strand you sniff appears to be dead, it may just be the neutral. You need to track down both sides to be sure.

[Brian Robertson]

John, when you find it like that, I,m curious how you express it in your report? Thanks Brian

[James Duffin]

I inspected a house a few years ago with hot K&T in the attic that was covered in insulation. I wrote it up in the report as a hazard that needed to be repaired. I did the same house two years and found the same thing. From what I understand the first buyer got $6000 to repair the wiring but did not use the money for that purpose. They ended up giving the second buyer the $6000 plus $2000 more. Hard to figure what's on folks mind sometimes.

[John Kogel]

John, when you find it like that, I,m curious how you express it in your report? Thanks BrianI say it may not be approved by insurance service providers. I recommend having a qualified electrician replace it.

This house still had the 60 amp service, so the service panel, weatherhead, service mast and meter can all need to be replaced as well. Big job.

[Robert Mattison]

Thanks for sending in the pictures, John K. Robert

[Jim Hintz]

One more thought concerning K&T and relates to Jerry's comment about the rubber insulation. When a fuse would blow out and a replacement wasn't handy, a penny was inserted into the socket on the fuse block and the blown fuse was put back in, bypassing the overload protection provided by the fuse. Not a thought was given to the excessive current cooking the rubber insulation covering the wire. You can bet it happened more often than not. Good Luck.....