It is safe, as long as the rubber/cloth covering is not damaged and any splices have been done correctly. If you are concerned, have it inspected by an electrician who is used to working on old houses. We have a few original lighting circuits wired with K&T; it's in very good condition and works fine. Romex is preferred, but it may be impractical to rewire unless you are removing ceilings and walls.
Here is an article that will tell you all about it:
I should have qualified my statement to mean "not as safe as modern romex." Maybe I have a little minor PTSD from the charred wood ceiling joist I uncovered where a knob and tube wire had a short at some point in the home's history. That said, they do last a long time. Its just they they can only get older, So if its convenient to replace it, that would be my choice. Not at the expense of a plaster wall however.
Replace it! I had a home that I had rewired when I purchased it. The electrician said the second floor(bedrooms and bath) were perfectly safe with the knob and tube wiring. Life was good for 14 years until I sold it. Three days before closing, the inspector required the wiring be replaced with romex. I was required to hire an electrician of their choosing and pay top dollar for plaster repair plus painting. It ended up costing me over 11,000. The original bid 14 years earlier was only 350.00. Saving a few pennies really ended up costing me. I was sure the knob and tube was safe but not everyone agrees.
FYI - the K&T will get hot if it is in contact with anything....the whole purpose of the knobs is to hold it away from the wood. Check to make sure no insulation has been added anywhere around the wiring - - if so then you need to address this issue immediately instead of at your leisure. Many people throw insulation in old homes not being aware that this prevents K&T wiring from releasing the heat and fire becomes more of a matter of when not If.
I would replace it and update your service. You can leave some of the old runs, not hook up, to show the history of the house, ( for fun ), were possible (basements, garages, attics). Just for your info I have over 35 years experience in historical restoration and preservation.
I would add that it is especially dangerous in attics and basements where there are exposed wires and connections to light fixtures. If you can not afford to replace it all at once then start with the service and outlets.The lighting circuits are less dangerous because they have less load to overheat the insulation. Finally, many Insurance companies will not insure homes with Knob and Tube Wiring.
Agree with most of the posters here. . . just replace it. Any good electrician should be able to pull the wire through with little to damage to your walls (you'll have to do some patching). And like others said, the risk is when the wiring is up against insulation (most likely in an attic crawl space).
Our 1880 Cottage had mostly knob and tube. We've been replacing it as we go. It cost us about 5K to replace 70-80% of it (and we live in Boston which is most likely a more expensive area to have that work done).
One other point is that insurance companies don't like that type of wiring, and the replacement will definitely earn you some brownie points when you decide to sell
Knob and tube is all new to us and the house we are moving into has mostly the old wiring (amongst other things). We also live in the Boston area, and are at a loss of locating an electrician who can help us with this huge project. Do you have one who you could recommend to us?
Knob and tube, if the cloth coating is still sound and porcelain knobs and tubes are not broken, very safe depending on previous work done by other electricians. If the knobs, tubes, or coating is broken replace or repair damage areas.