From: John De Armond
Newsgroups: alt.energy.homepower
Subject: Re: Question about knob and tube wiring
Date: Fri, 02 Nov 2007 09:14:18 -0400
Message-ID: <tk7mi31m9lket65euc4jh1eq1lnl7bmee2@4ax.com>

On Thu, 1 Nov 2007 20:03:52 -0500, "Jim" <jim@horne.corn> wrote:

>>   This wiki article explains it (and the issues) pretty well.
>> http://en.wikipedia.org/wiki/Knob_and_tube_wiring
>>
>> Vaughn
>    Wow. That's pretty freaky! LOL!!! Glad I never had to muck about with
>that.

Why freaky?  Properly done K&T is probably the safest wiring method for domestic
wiring.  In my experience most of it was properly done.  Problems usually arise
either when overly large breakers or fuses are installed or when someone mucks around
with it who doesn't know what he's doing.

Consider the advantages.  Opposite polarity conductors are always separated.  Copper
never touches any flammable structural materials.  The most a nail driven through a
wire can do is break the circuit.  All wire joints must be mechanically secure before
being soldered.  It works when wet and there is no mechanism to wick water back up
the conductors as there is in romex.

The issues raised in the Wiki article are mostly strawmen.  The rubber insulation's
tendency to degrade is mostly irrelevant since the wire never touches anything except
porcelain except in the junction box and there it's inside loam (the proper term for
what the article calls sleeving).  Bare wire could just as well be used.

It is irrelevant where junctions are because of the joining method.  For a solid tap,
the wire is wrapped behind itself one turn, looped back over itself and wrapped in
the other direction.  Stranded wire is split into two groups and twisted in opposite
directions.  In both instances, the joint is then soldered.

Junctions weren't just covered with cloth tape as described in the article.  The
first layer was self-vulcanizing rubber tape that provided the electrical insulation.
The second layer was friction tape, rubberized canvas, that provided mechanical
protection.

Lack of a grounding conductor had nothing to do with the K&T technique.  Indeed, I've
seen installations where there WERE ground conductors.

Waterproof wiring, as around a pool, was lead-encased and the junctions were lead
wiped after splicing (a technique that involves wiping partially molten lead between
the sheath and a sleeve to make a continuous lead cover), resulting in hermetic
joints.

What pushed W&T out of the forefront was not that it was inherently unsafe but that
it was very labor-intensive to install.  It also required a REAL trained electrician
and not just some wire-twister come in off the street.  An electrician in those days
typically served a 3-4 year apprenticeship.

Relative to this thread, I would NOT go in and rip out sound K&T wiring.  As I said
in my one-sentence post, make sure that the overcurrent protection is appropriate for
the size wire involved and then go with it.

John