Using THHN or THWN with knob & Tube

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sfav8r

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San Francisco Bay Area
We are working on a project where there is existing K&T wiring extending through the area we are working on. We are only adding new circuits and will not be dealing with the old wiring at all. I noticed that at some point the old K&T was repaired or extended using THHW and THHN. My first reaction was that this was not code compliant. I then anticipated that we would be required to fix this even though we were not dealing with the old circuits. However, in reading article 394.104 (article referring to knob & tube wiring), it says conductors shall be of a type specified by article 310. 310 doesn't give me any information that would lead me to believe it can't be used in this application. Is it approved?

Thanks.
 
mdshunk

mdshunk

Senior Member
Location
Right here.
I've worked on late 60's K&T that was done with type TW. THHN is still part of chapter 3 too.

I've got an old wire catalog that lists megger readings for old "code" wire, that was used popularly with K&T. Believe me, THHN is superior in every way with respect to dielectric strength.
 
e57

e57

Senior Member
Location
San Francisco, CA
THHN, and THHW are allowed. In fact much of the more recently installed K&T, before SF allowed NM cable to be installed in the late 50's~early 60's is solid THW. I will also add a word of warning to those who may come across these very late installations where THW, or THHW is present: They also coincide with a code change that allowed 3-wire circuits. So just about all that are wired with any thermoplastic wiring will be 3-wire K&T! The good news is that there was an economic slump, and there wasn't alot of work going on at the time... Also what is even worse than 3-wire K&T, is that there was also a massive decline in workmanship, if you unwrap the splices of this stuff, you'll find some very nice splices that never got soldered at all, and have a tendency to fail.... Many of the older Electricians actually blame that decline in workmanship on NM...

A little more history here.... SF would not allow NM for a much longer time than the rest of the country for a few reasons. Most of them are political, but this is the lighter side of it, without getting into Union/non-union debate.... A now retired SF Inspector told me that there was such a debate about NM being an inferior wiring method that it was actually banned from being installed, or even sold by SF supply houses. It was not until a wrongful death suit blamed on Knob and Tube (See above) that the change occurred. That death was the daughter of who would become our short-lived Mayor Moscone. Who was shot my a man (Another Elected Official) who got off the murder rap because he ate a "Twinky"!!! :rolleyes: And the woman who took over for him - Diane Feinstein, now our Senator, finalized the push to allow NM in San Francisco, in honor of the man who got into politics supposedly due to the death of his daughter.... A (Now 80 year old) Irishman I used to work for, whom I affectionately refer to as "Uncle Joe" - Sighs and says, "Twinky Wiring", every time he sees thermoplastic K&T.
 
peter d

peter d

Senior Member
Location
New England
That has to be the most...ummmmm......what's the word?.....interesting story I've ever heard about plain old NM cable. :D

e57 said:
A little more history here.... SF would not allow NM for a much longer time than the rest of the country for a few reasons. Most of them are political, but this is the lighter side of it, without getting into Union/non-union debate.... A now retired SF Inspector told me that there was such a debate about NM being an inferior wiring method that it was actually banned from being installed, or even sold by SF supply houses. It was not until a wrongful death suit blamed on Knob and Tube (See above) that the change occurred. That death was the daughter of who would become our short-lived Mayor Moscone. Who was shot my a man (Another Elected Official) who got off the murder rap because he ate a "Twinky"!!! :rolleyes: And the woman who took over for him - Diane Feinstein, now our Senator, finalized the push to allow NM in San Francisco, in honor of the man who got into politics supposedly due to the death of his daughter.... A (Now 80 year old) Irishman I used to work for, whom I affectionately refer to as "Uncle Joe" - Sighs and says, "Twinky Wiring", every time he sees thermoplastic K&T.
Click to expand...
 
e57

e57

Senior Member
Location
San Francisco, CA
Oh twinkies have some seriously strange lore in this town... (To include rioting, and Jonestown.) Granted I got that story from a very old - very wacky inspector, but given the chance, the better part of 20 years of local history can be linked to the twinkie by 6 degrees of seperation... :grin:
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
e57 said:
the better part of 20 years of local history can be linked to the twinkie by 6 degrees of seperation... :grin:
Click to expand...

So these Twinkies are not actually in phase, that could explain this phenomena. :D

Has anyone else included banning Twinkies in their employee rules? It is right above alcohol and illegal substances / drugs in our company handbook. ;)

Roger
 
e57

e57

Senior Member
Location
San Francisco, CA
Oh I should have taken pictures.... I was stuffing twinkies into a monkey-face today.... :grin:

Roger, they would also have to ban water....
 
roger

roger

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Staff member
Location
Fl
Occupation
Retired Electrician
e57 said:
Roger, they would also have to ban water....
Click to expand...

Nope, our company just includes Twinkies, Drugs, and Alcohol. I will talk to them about the water though. :D

Roger
 
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