I'm in the process of decommissioning the last active (hopefully) knob and tube circuit in my house (I'm in the U.S.). The problem is that about 90% of the lighting in the house is on this circuit, and I won't have access to re-wire two rooms until I remodel them in the spring and there isn't any good way to get NM cable from those two rooms to the service box until the walls come down in a couple months.

Coincidentally, a friend of mine found a bunch of new old stock A-head connectors in a bag in his attic exactly like this one in my basement:

enter image description here

My understanding is that these are still allowable under NEC 300.16 and would give me an easy way to keep the 2 problem rooms live until I can finish replacing the circuit. Am I correct that this is still legit? If so, are there any issues with using NOS hardware for the splice? I don't really want to disturb the old wiring that I'm not immediately replacing any more than I have to, so this seems like a better solution than a junction box.

2 Answers 2


The article you need to refer to is 394.

Here is an excerpt that applies to your situation.

II. Installation

394.10 Uses Permitted. Concealed knob-and-tube wiring shall be permitted to be installed in the hollow spaces of walls and ceilings, or in unfinished attics and roof spaces as provided by 394.23, only as follows:

(1) For extensions of existing installations

(2) Elsewhere by special permission

Many jurisdictions don't allow K & T unless it is a historical house. For your temporary situation, unless you are pulling a permit and getting inspected, extension of the existing system would seem reasonable.

You should replace it with a more modern grounded wiring method as soon as is practical though.

Happy New Year!

  • Just to clarify, I'm not extending the circuit. Everything between the service box and the splice would be replaced - the splice would feed the existing K&T that remained.
    – Comintern
    Jan 1, 2016 at 20:51
  • I just read your post again and the code does not allow for basement wiring in K&T permanently even an extension. However, temporary wiring is allowed under article 590.3 during periods of construction. If you are not being inspected until later than it is a moot point. 590.3 Time Constraints. (A) During the Period of Construction. Temporary electric power and lighting installations shall be permitted during the period of construction, remodeling, maintenance, repair, or demolition of buildings, structures, equipment, or similar activities.
    – ArchonOSX
    Jan 1, 2016 at 21:09
  • The picture from the basement is just an example of the connection I'm considering using (and all of that is coming down in a couple of days) - the feed into the old wiring would be in the attic. You do raise a good point about temporary wiring though - I could always pull the second permit 5 months early. They don't expire for 18 months in my jurisdiction.
    – Comintern
    Jan 1, 2016 at 21:29

In my area (Oregon) any updates need to meet current code , that means boxes for splices, repairs are allowed "as built" so you may be in a gray area , home owners regularly do repairs that do not meet code but a licensed electrician is risking his/ her license not to put it in a box. I would think the risk is low as you are going to make it right soon but wire nuts were not the norm back then solid crimps were so if there was a fire the wire nut would be identified as a update if something happened and was found during an investigation.

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