Can knob and tube electric be inactive?

Question

I did an inspection on a 4 unit yesterday.  In the basement is 1 meter and 2 panels with circuit breakers.  The wires are newer and my inspector noted some wires were not enough amps.  Then we get to the attic and every rafter is covered in knob and tube electric.  Any chance it is inactive and just never removed?

Stephen Joyner · Answer

Here is what an electrician will tell you about knob and tube wiring.

1) is it safe: yes as long as it is the same as it was when installed.

2) what are the dangers: Fire, death, electrical shock.

3) should I remove it: NO unqualified person should remove it refer to number two if you have questions.

4) if I have knob and tube is it okay to install three prong outlet. Maybe.... Only if someone has install a ground in the box and it is verified to be a grounded. Most systems are ungrounded.

5) should I remove it: yes and no. Yes it should be removed so that you have a grounded system. Plan and simple a grounded system is a  safer system. No if it has not be altered or touched in anyway then it will work just fine just as it has for the last 80 years or longer.

6) Where is knobs and tube in In use today: the most common place I still see it being used is for lighting. A lot of times people have done remodels over the years and the electrician or who ever did the work has removed all the wiring to outlets on the system and rewired them. Because they do not really mess with the wiring to the lights or to the switches the are fairly safe.

7) Wher do you still see this wiring: the most common places to still find this wiring is in small towns and cities that have not had large amounts of change. I have never seen in Los Angeles or in some of the surrounding city's. But when I lived in Northern California it was a common thing to see. I have talked with other electrician over the years and it seems that the only ones that still encounter it are the one that where living in smaller communities.

8) Is it possible that the knob and tube wire is dead and left in the wall and ceiling: yes it is very common to find abounded wire in the walls not so likely in the ceiling. Most electrician are professionals and the remove everything that they abbanded so that there is no confusion to what is working what is not. As for wall sometimes they do not get opened all the way and it is hard to remove everything.

Now that I have answered some of the questions here is more information and my opinions on this matter. Knob and tube wiring was used in the wiring of houses from about 1900 to the 1930's. With all things there has been advancements that have made things better. Knob and tube wiring runs though the walls and rafters with a neutral wire and voltage wires that ran through insulators through the wood know as tubes. And then the knobs were used to hold the wire tight and straight to protect them from damage. At the time this was a very good system. But it is not a grounded system. Because of time, wire has been degraded, damaged, and scabed into to run other items. Even when done properly this weekens the sheathing of the wire and weekens it. Which then can cause life treating issues. I believe that this system is obsolete and over the years many people have altered the system making it unsafe. With anything time is a factor in the safety of the system. Most knob and tube wiring is a powerd screw in fuses. A whole another issue but most fuses are the wrong size for what it supposed to do. I always try and incurrage my clients to remove all of it and bring up to code.

Aaron Montague · Answer

@Brie Schmidt

I'd guess "more than likely."  You can run the same voltmeter test that you do with standard outlets.

My electricians say "it isn't all that bad" unfortunately my insurance company does NOT share that opinion.  Make sure it it replaced if active and capped if not.  You can remove it yourself once the juice has been shut off.  But I'm sure you electrician would be glad to do it for $105/hour :)

Mark B. · Answer

About 10 years ago I found the most beautiful example of knob and tube in a San Francisco basement. You could trace the wires from the knife switch all the way to the light, might as well have been a new installation. The insurance underwriter was not happy, since the owner had promised that it would be removed.

Adam Johnson · Answer

It has already been stated to get a "tick" tester, as they are commonly referred.  More on that in a second.  First and foremost, never, ever, ever ASSUME any wire/circuit is dead without first verifying it.  I have encountered some potentially deadly situations where my first assumption was, "there is no way that is live", only to find out with my "tick" tester that it did, in fact carry voltage.

In my opinion, the cost of a decent tester is worth far more than going "cheap".  I have a decent one in the door of my truck and use it regularly.  It cost me maybe $ 30-40 and has adjustable sensitivity.  I usually start with it at the highest sensitivity.  When I get close to a live circuit, it flashes a light and beeps.  Mine will pick up live lines behind drywall, power at switches through plates, as well as common cable sheathing.

I am not an electrician, but I work around it enough to know when to take 5 minutes extra to get my tester from the truck.  Ever run a screw through drywall to hang a picture and run it through a wire?  Maybe I should add, "yet"?  Money well spent.

Gilbert Dominguez · Answer

When it comes to knob and tube you either should be very familiar with checking for live wires or let an electrician do it for you. Allot of places have knob and tube along with modern Romex wiring and the knob and tube is still being used to service the house electrical system. Be careful. If your insurance company will not insure a house with knob and tube then of course it either needs to be removed or updated which mean rewired with modern wiring systems up to code. This of course means an expense.

If you simply want to check if the wire is live or not a simple tester will do the job. However testers do fail sometimes and are not the best of quality so you should really know what you are doing as it could very well be life threatening. Do not take anything electrical as a joke, it is serious business.

In any case I would want an electrician to check out the electrical system of any property I intended to buy regardless.

Steve Babiak · Answer

If there are ceiling light fixtures below those knob and tube runs, I would not be surprised to find that the knob and tube is still live and in service.

Ken P. · Answer

In all likelihood it is inactive.  My brothers' rental properties in upstate NY, built late in the 19th century, often have knob and tube wiring still in place that probably hasn't been used since the FDR Administration.  The knob and tube wiring runs parallel to the 1880s gas lines (for gas lighting) and mid-century BX cables and modern Romex.

Carl C. · Answer

It can definitely be inactive but some insurance companies (mine) will require that even inactive knob and tube be completely removed from the house. Nathan's recommendation for the voltage stick is your quickest and cheapest option to check for activity. Good luck!

Can knob and tube electric be inactive?

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