knob and tube in insulation

[Hendrix]

How's this:

What, no splices in the knob ?

 

[al hildenbrand]

What, no splices in the knob ?

I'll bet there's one at the top left of the photo, behind the joist.

 

[Jim W in Tampa]

If not missused k & T is about the most safe method ever out there. But it was never intended to get insulation.

 

[e57]

If not missused k & T is about the most safe method ever out there. But it was never intended to get insulation.

I have seen a few that actually were intended to be insulated... More below.

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.

Locally - which is an exception to the norm.... K&T was installed clear and through the 60's and into the early 70's.* Some of those were insulated when the walls were closed initially. I have remodeled and demo'ed some of these buildings and a few of them had some pockets where they did not insulate around splices. And only once in a much older K&T job with a pretty decent splice - with insulation installed over it for a long time did I find an area where there was some heat damage at a splice in insulation.

I used to do inspections of wiring in attics that were to be insulated here for an insulation contractor. They often used plastic cones or plywood 'tents' over splice areas - a practice started due to me refusing a few of their jobs. Normally the work consisted of inspecting and correcting the violations - then I found some of the 'original' installs where insulation was charred at splices that were poorly made. (Which got me more skeptical) That said - the conductor length without splices (if the insulation is in good condition) does not generate too much heat on its own - not enough to be hazardous. Poorly made splices on the other hand could be a fire hazard. And short of load testing them and checking temp rise - I suggest 'tenting' the splices from insulation contact.

As mentioned insulating K&T is allowed by the California Electrical Code - and it is up to the EC who does the inspection to assess the wiring and each situation - sign a form and file it with the AHJ.....


(* That new fangled NM cable was blamed for fires and death by a certain group of electrical workers locally in the 50's. Consequentially they kept NM from being used in SF for a few decades, mostly due to feeling that NM was a 'dumbing down the trade' to where less skilled workers could do the work. IMO mostly due to protectionism, but then again - much of the 70's and early 80's NM work here was just horrible!!!!)

 

[al hildenbrand]

(* That new fangled NM cable was blamed for fires and death by a certain group of electrical workers locally in the 50's. Consequentially they kept NM from being used in SF for a few decades, mostly due to feeling that NM was a 'dumbing down the trade' to where less skilled workers could do the work. IMO mostly due to protectionism . . . )

The Minneapolis / St. Paul area had a similar bit of history. The shift to an "all metal code" happened in the Thirties. All power & light wiring had to be covered by metal, so there is a lot of Armored Cable, Flex and EMT installed. The Seventies saw the relaxation of this requirement thereby allowing NonMetallics back in.

The out lying (then, they're "inner ring" now) suburbs, villages and townships didn't limit the wiring methods available to ECs.

 

[LarryFine]

Normally the work consisted of inspecting and correcting the violations - then I found some of the 'original' installs where insulation was charred at splices that were poorly made.

That's the fault of the wiring installation, not the wiring method.

 

[e57]

That's the fault of the wiring installation, not the wiring method.

I agree 100%

As for the dumbing down of the trade.... I also agree. There seemed to be a reduction in the amount of care, attention to detail, and quality coinciding with that switch. At which point some of the K&T work suffered too.