knob and tube in insulation

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Mulrooney

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One of my customers is at a weatherization seminar and the teacher is stating that if knob and tube is running vertically then it can be encapsulated in blown in insulation because it disipates the heat better. He states this is in the NEC, I can't find that. Anyone know something I don't.
 
Mulrooney said:
One of my customers is at a weatherization seminar and the teacher is stating that if knob and tube is running vertically then it can be encapsulated in blown in insulation because it disipates the heat better. He states this is in the NEC, I can't find that. Anyone know something I don't.
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I believe that 394.12 (5) says no.
 
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Absolutely not allowed.

394.12 Concealed knob and tube wiring shall not be used in the following:

Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed in place insulating material that envelops the conductors
 
Mulrooney said:
One of my customers is at a weatherization seminar and the teacher is stating that if knob and tube is running vertically then it can be encapsulated in blown in insulation because it disipates the heat better. He states this is in the NEC, I can't find that. Anyone know something I don't.
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It's a good thing the customer has you, who knows better
 
electricmanscott said:
Absolutely not allowed.

394.12 Concealed knob and tube wiring shall not be used in the following:

Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed in place insulating material that envelops the conductors
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Yet I see it all the time in houses in S. Boston, Dorchester, and Quincy. I mean ALL the time.
 
electricmanscott said:
Absolutely not allowed.

394.12 Concealed knob and tube wiring shall not be used in the following:

Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed in place insulating material that envelops the conductors
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The language you are quoting first appeared in the 1987 NEC, back when it was in Article 324-4. Before adoption of the 1987 NEC, there was no restriction, as far as the NEC was concerned.

This issue is not black and white. When was the '87 NEC first enforced in the jurisdiction where the insulation is installed? Adding insulation over already insulated K&T is something different than insulating K&T for the first time.

Given that K&T was effectively no longer installed by the '50s, I have to ask, how many of those original concealed K&T installations in open (un-insulated) stud and joist cavities actually survived energy conservation efforts prior to enforcement of the '87 NEC? Darn few, I'll bet.

Of course we see K&T fully enveloped in insulation, and it was blessed by the NEC's silence, until the 1987 NEC went into effect.
 
jaylectricity said:
Yet I see it all the time in houses in S. Boston, Dorchester, and Quincy. I mean ALL the time.
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Me too. Legit insulation contractors know not to do this. Usually the ones hired by utility companies won't insulate unless there is no k&t or they get a letter from an electrician saying any apparent K&T is no longer in use.
 
Code aside, I've seen K&T wiring survive intact under conditions that would liquify the plastic on modern NM cable.

Proper K&T installations could theoretically use bare conductors (outside of boxes); the same can't be said about NM.
 
al hildenbrand said:
The language you are quoting first appeared in the 1987 NEC, back when it was in Article 324-4. Before adoption of the 1987 NEC, there was no restriction, as far as the NEC was concerned.

This issue is not black and white. When was the '87 NEC first enforced in the jurisdiction where the insulation is installed? Adding insulation over already insulated K&T is something different than insulating K&T for the first time.

Given that K&T was effectively no longer installed by the '50s, I have to ask, how many of those original concealed K&T installations in open (un-insulated) stud and joist cavities actually survived energy conservation efforts prior to enforcement of the '87 NEC? Darn few, I'll bet.

Of course we see K&T fully enveloped in insulation, and it was blessed by the NEC's silence, until the 1987 NEC went into effect.
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That's something that needs looked into. I see your point and not sure what an inspector could say or do. Do think insurance companies and lenders might back off fast on them.
Who in there right mind would live in a situation like this ? Knowing that NEC sees it as a hazard would you simply not care because the unsafe system was legal at the time ?
 
Jim W in Tampa said:
Who in there right mind would live in a situation like this ?
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Seems that most (I'd guess 90%) of the inner ring of Minneapolis / St. Paul is happily living in dwellings built before 1950, and 70% of those (my guess) are K&T.
Jim W in Tampa said:
Knowing that NEC sees it as a hazard would you simply not care because the unsafe system was legal at the time ?
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A friend of mine got a good offer on adding blown fiber glass insulation in his attic. The insulation contractor, working for the corporation that made the offer, balked at adding insulation on already fiber glass insulated K&T. On his behalf, I contacted the local electrical inspector who stated that the K&T in fiber glass was just fine. The only issue his AHJ had was foams, as there are no studies of the foam's effect on the old insulation.
 
al hildenbrand said:
Seems that most (I'd guess 90%) of the inner ring of Minneapolis / St. Paul is happily living in dwellings built before 1950, and 70% of those (my guess) are K&T. A friend of mine got a good offer on adding blown fiber glass insulation in his attic. The insulation contractor, working for the corporation that made the offer, balked at adding insulation on already fiber glass insulated K&T. On his behalf, I contacted the local electrical inspector who stated that the K&T in fiber glass was just fine. The only issue his AHJ had was foams, as there are no studies of the foam's effect on the old insulation.
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Foam is flamable so i can understand saying no to that.
My understanding is insulation of any kind would trap heat on that old wiring. I really am not sure if that is serious enough or not. I do recall one job i was on that was a 1920's home in old part of Tampa. The remodel exsposed the problem along with some other not to code items. It added about 10 k to job but when done job turned out fantastic. They were very happy that i caused almost no damage to the finish. The GC matched everything from windows to sideing ,would been proud to own the old house.
 
Thanks for your input guys, aside from the insulation around K&T subject, ive found the worst condition K&T to be in light fixture boxes. This is mostly from people putting 100 watt lamps in 60 watt fixtures I assume. It may even be from the correct lamp. You just touch the wires and the insulation falls off.
 
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