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-   -   insulate over old knob-and-tube wiring? (

Bru 11-01-2010 07:32 PM

insulate over old knob-and-tube wiring?
I'm in a house built in the '20s, which still has a few circuits on the old 2-wire knob & tube wiring, some of which runs across the floor joists in the attic. I really need to add a foot or so of fibreglas insulation to the attic, but am not in a position presently to rewiire the old circuits.
Is there any danger to putting the fibreglas insulation batts over the top of the old wiring?
Thanks for any suggestions or info.

paul52446m 11-01-2010 09:15 PM

I don't think i would do that. The more amps that you run through a wire, the hotter the wire gets. So if you have the insulation around these old wires that can get very hot. The covering on the wires is already old, cracked, and if you heat it up a lot more the coating will really get bad.
I would rewire before insulation. The air around the wires is what cools them. Later Paul

JoeD 11-02-2010 07:12 AM

K&T is meant to be an open air system for cooling purposes. You are not supposed to bury it in insulation.

Bru 11-02-2010 07:17 AM

Thanks, guys. Sure am glad I asked. Looks like there's an electrician in my future.

Redbirdseven 11-03-2010 03:17 PM

I will just jump in here and agree with Paul and Joe .. Never cover K&T just to risky to take that chance.

BBrown 11-06-2010 10:56 PM

I have uncovered knob and tube wiring with scorch marks inside the cavities. They are simply undersized for today's loads. Personally, if I can see it, I replace it.

speedy petey 11-07-2010 04:56 AM


Originally Posted by BBrown (Post 50910)
They are simply undersized for today's loads.

This is not exactly accurate. It is not that the wire is undersized, more often they are over-fused by people removing or replacing 15's and 20's with 30's.

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