My parents recently purchased a mid-1920s house and are doing some work on it as a retirement home. We had an electrician out to the house the other day; upon peering behind one of the outlets, he made an offhand comment about the outlet (and thus, probably all the outlets) using knob-and-tube.

This had not come up on either inspection report (my parents' or the seller's), so we were surprised. We plan on having a few more electricians out to get additional opinions, but we were wondering if there are any telltale signs of knob-and-tube, particularly when looking at an outlet?

Everything in the unfinished basement looks fine based on criteria we found online (e.g., breaker box looks like it has armored cable); we have yet to check the attic. There was a major addition added on the house ~30 years ago, so it's possible something was done to remove it then (if the house ever had it in the first place). We would like to be a bit more knowledgeable on this when talking with other electricians.

  • AFCI breakers are your friend, if the neutrals aren't too tangled up. Jul 15, 2017 at 5:19
  • Have you read this yet: en.m.wikipedia.org/wiki/Knob-and-tube_wiring
    – ArchonOSX
    Jul 15, 2017 at 8:11
  • @ArchonOSX Yes, we have, which is what caused us to go check the basement first, since those pictorial examples are seem based in attics/basements. We're particularly curious about what an electrician can see behind an outlet that would cause him to say we have knob-and-tube. Jul 15, 2017 at 9:04

1 Answer 1


The best way to see if you have knob and tube wiring is to inspect the attic and see if is running through the rafters up there. Other than that you can open up a switch or receptacle and look for small ceramic "tubes" that will be used for bushing in the boxes. Also knob and tube is an ungrounded system so look for receptacles that have only two slots instead of three and of course ground wires in any boxes.

The areas that are remodeled thirty years ago would have to be wired under the 1984 code which would include ground wires, but that does not mean the areas that weren't touched by the remodel would be updated even though it would have been a good idea. Usually what happens is the Panel is upgraded and maybe relocated and the new addition is run and the existing wiring is back fed into the new Panel.

  • 1
    When the upgrades were done it is possible the k&t was left in the walls This was a code approved way of doing upgrades in the last code 2014 not sure if still ok with the latest code revision.
    – Ed Beal
    Jul 15, 2017 at 18:48

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