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jackdp 10-23-2005 09:57 PM

How safe is knob and tube wiring?
My wife and I recently bought an old farmhouse built in the late 1800's. Its all wood construction with plaster walls, a previous owner installed drop ceilings and paneling. It looks like the original wiring is knob and tube. Most of the ground floor has been updated with new wiring, the wires to most of the receptacles on the 2nd floor have been upgraded as well. Every thing comes from a 100A breaker panel. My best guess is that the ceiling fixtures in every room except the kitchen and 1st floor bath are still knob and tube wires. My question is how safe is K&T for low loads like light fixtures and wall outlets? All the appliances, computer, entertainment center etc. are on newer wiring. Is this a big problem that should be addressed immediately? TIA

Mike Swearingen 10-24-2005 12:38 AM

I am NOT an electrican, just a long-time DIYer, so I'll pass along what I've seen some pro electricians say about it, until one comes along to answer your question.
A. It is relatively "safe" as long as it has not been disturbed in any way (insulation blown into walls and ceilings with it, mice and rats, house settling, mishandling it when re-wiring to it, etc.). K&T is 14 gauge (15 amp circuit breakers only) and has insulation that is very brittle, which crumbles off easily. That is the primary fire hazard with it.
B. Replace all ungrounded/unsafe K&T as soon as you can.
My elderly mother-in-law, rest her soul, had some ceiling K&T in an 1883 National Register of Historic Homes house, and let her homeowner's insurance lapse one year. The following year, the home burned down for a $650,000 uninsured loss. She managed to escape, but a family dog died in the fire.
Fire investigators traced it directly to K&T ceiling wiring.
I would replace K&T completely and upgrade the main service to a 200 amp breaker panel. Besides structural considerations, that would be my highest priority. Although it is perfectly legal to sell houses with K&T in them (I'm a real estate broker), I always highly recommend that the buyer replace it a.s.a.p. Why try to live with such a hazard? Replacing it should save on your homeowner's insurance, too.
Good luck!

jackdp 10-24-2005 11:02 AM

How hard is it to replace? I work for a sound company and we have done sound system installations in old churches in the past, so I'm somewhat experienced in pulling wire through old walls. Most of the wiring from receptacle to receptacle has been replaced. My best guess is that the K&T that remains is the run from the basement to a junction somewhere that feeds the newer romex on the second floor and the K&T for ceiling lights. Has anyone here had this replaced before? Does anyone know a ballpark cost? TIA

Mike Swearingen 10-24-2005 11:44 AM

The difficulty and cost are directly related to the specific structure of the individual house and what exactly needs to be done to run the new wiring. Get three electrical contractor quotes, if you like.
Completely replacing it can be a DIY job, if you have the electrical skills and experience, but tying into any old K&T is best left to a pro who is knowledgeable and experienced at it.
I've seen downstairs ceiling wiring done to replace K&T by accessing runs through the upstairs flooring, rather than going up through the plaster ceilings.

jproffer 10-24-2005 04:37 PM

To give you an idea of what the NEC thinks of K & T safety, you can still LEAVE it in place, but you can't put in new K & T wiring anymore (or even buy it anywhere I've ever seen). Take that how you wish, but thats the code in 2005. (and well before 2005 for that matter)

K2eoj 10-25-2005 12:31 AM

I'm always more concerned with the type of breaker panel that is in the house. If i had K&T and a Federal Pacific panel i would be very concerned. There is a bunch of stuff on the net about FP panels and how unsafe they might be. If i had K&T and a good panel I would feel safe. HS

jackdp 10-27-2005 12:39 PM

I feel somewhat safe. All the insulation I can see seems to be in excellent condition (can't see inside walls or ceilings). I've figured with Ohms law that if I turn on every light on the K&T circuit at the same time I would draw about 10 amps, and that just won't happen.
Actually, it would seem that the only place I can find the K&T is in 3 light switches, at ceiling fixtures and in the attic. 14ga. NM comes out of 15amp breakers (Crouse-Hinds panel circa 1970's) goes to 2 J-boxes in the basement, then K&T comes out of the j-boxes and runs up into the walls, but inside all the receptacles I've opened is 14ga. NM. Its like someone almost rewired the whole house..almost. Even more stupid is the fact that someone actually pulled new circuits of 14ga NM to the 2nd floor but just put in new outlets and didn't tie the existing outlets in. Somwhere between the basement and the 2nd floor there must be a large junction with K&T coming in and NM going out...if I could only find it....

mighty anvil 10-27-2005 09:01 PM

Safety is difficult to evaluate with K&T. My house was built in 1891 with gas lighting and was wired in 1903 with K&T with no problems for 80 years. When I started to rewire I found that BX cable installed in the 50's was far more dangerous than the K&T. The insulated wire in the BX cable had crumbled in the metal boxes and bare wires were a serious hazard. The ground, of course, was only through the metal cable sheathing and was not reliable. Fortunately, it had not been stapled anywhere so I was able to pull new wires through as I removed the BX. I had to replace all of the BX before starting on the K&T. The K&T was in perfect condition. All wires were oversized copper (aprox. #10) and the insulation was thick and difficult to remove with a knife. I could find no deterioration anywhere. Since the wires were held apart and insulated with ceramic tubes at joist penetrations and thick flexible tubes elsewhere, it appeared to be very safe. The only feature missing was the equipment ground and of course the panel was a nightmare.

I would replace all K&T wiring but I would rate it as safer than a lot of the wiring installed in the 50's & 60's.

Mike Swearingen 10-29-2005 10:50 AM

Mighty Anvil,
Your avatar looks like an old Nam photo.
199th Light Infantry Brigade (Separate), Nov 67-Nov 68 here. An outstanding, highly decorated unit. You?

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