Re:Air-to-Air Heat Exchangers for Healthier Energy-Efficient...
by mhb on Saturday February 04, 2023 @12:34PM
(#34656268)
Thanks. Good to know. But probably worth mentioning that, even though you can insulate around knob and tube where local jurisdictions allow it:
"K&T wiring is designed to dissipate heat into free air, and insulation will disturb this process. Insulation around K&T wires will cause heat to build up, and this creates a fire hazard. The 2008 National Electrical Code (NEC) requires that this wiring system not be covered by insulation."
Re:Air-to-Air Heat Exchangers for Healthier Energy-Efficient...
by drjasonharrison on Saturday February 04, 2023 @02:00PM
(#34657045)
I wonder how often this actually is a problem, in that the owner looks at knob and tube wiring and keeps it for the heritage value. My parents were ripping it out in the 1970s from a 1920s home. I know that heritage designations often require using the original construction techniques but do they prevent upgrades to the electrical system?
"I'm sorry sir but your grandparents didn't have grounded outlets so you can't install have them either."
Re:Air-to-Air Heat Exchangers for Healthier Energy-Efficient...
by mhb on Saturday February 04, 2023 @04:29PM
(#34658513)
The problem, at least in my case, is that my 1930 house has k&t wiring and little/no insulation. The easiest way to add insulation would be to blow it in through drilled holes. This is a lot less involved than rewiring the house.
I have no affection for the wiring - nostalgic or otherwise.
And, yes, vapor issues.
https://www.nachi.org/knob-and-tube.htm
In any case, if you overheat Romex and destroy the insulation, you can create a line-to-ground-or-neutral arc or short. If you overheat knob and tube and destroy the insulation, you are quite unlikely to cause an actual problem — there’s nothing nearby for it to short to.
Modern insulation tolerates rather higher temperature than old insulation, and knob and tube has plenty of other problems, but this isn’t really one of them.
(If GCFIs on branch circuits or feeders were widely deployed, even at higher thresholds than 5mA, and everyone used either grounded metallic conduit or bundles of wire with a bare ground in the middle (like Romex or NM-B), then insulation failures would be quickly detected.)