Is fiberglass insulation over ancient ball and wire wiring a fire hazard?

Question

That is, is it more of a hazard than ancient ball and wire wiring without insulation on top of it? Someone I know said it was, but that makes no sense to me; it's a superb electrical insulator, and it can't burn. It's made from extremely fine fibers of glass. Perhaps the theory is it could allow heat to build up and cause something else to catch fire.  Maybe that's the thinking.

Anonymous · Accepted Answer

If its in contact with the wiring its a hazard if it gets wet.
BTW its called knob and tube and the wire actually had insulation of sorts at one time 90 years ago.

kenD · Answer

In our area it is against the building code to add any type of insulation on top of knob and tub wiring.  The reason is that it allows heat to build up in the old wires. Insulation companies will refuse to insulate attics until the wiring is upgraded.

? · Answer

THINK is right.  That old wiring was only intended to have a lifespan of 20 years, tops.  You don't want ANYTHING in contact with it, even theoretically non conductive fiberglass insulation.   First of all, insulation is NOT pure fiberglass, it has chemicals in it, too.  Even if it had been manufactured pure (it's not though) who is to say that it didn't build up enough dust and contamination to cause your electricity to track.  Not to mention what happens if it gets wet, which happens more often than any of us would like.  
I agree with THINK.  Don't do it.

William B · Answer

no
 my house has knob & tube wiring its insulated with fiber glass 
glass will not conduct  electricity, your better to have it covered than open, 
 my house was built  around  1814 and still has the old type wiring  with a new breaker box

Anonymous · Answer

fiberglass insulation is inflammable if it is of the kraft paper type, then yes, the paper can catch on fire

Is fiberglass insulation over ancient ball and wire wiring a fire hazard?

5 Answers