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Date: Sat, 07 Jan 2006 23:27:09 -0500
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From: "Dan Schaefer" <dfs155@adelphia.net>
Subject: Re: Fast-Ons et al.
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I'm in total agreement with Brent regarding wire with PVC insulation being
unsuitable for use in any airplane, however I'd like to add Teflon
insulation to the proscribed list as well, for the following reasons.

When Teflon was new and the only game in town, it was used extensively in
aircraft wiring. Unfortunately, it had two very undesireable
characteristics: one was perhaps merely anecdotal but the other was an
unforseen and potentially catastrophic failure mode.

The first problem is purportedly caused by the use of thermal strippers
(removal of the insulation via a red-hot wire loop) where the Teflon gives
off what is supposedly a toxic gas. Don't know how true this is but I do
remember that back in the '60's, some production workers who did a lot of
the Teflon wire stripping at a small electronics company where I once
worked, began complaining of persistant flu-like symptoms. After adding
simple vacuum hoods over the strippers, to suck up the smoke and other
gasses, the problems disappeared.

The second problem (with which I do have direct experience) is the tendency
of Teflon to cold-flow over time when subjected to pressure being applied
when bent around a sharp edge. This may not be as big a problem in composite
structures, but in a metal airplane, or behind a panel with metal parts,
this can lead to the insulation being effectively cut through resulting in a
short with the ensuing mayhem that can bring.

Tefzel insulation (see Brent's note to the list) is highly resistant to the
cold-flow problem - the stuff is really tough - however, the gasses it gives
off when hot-wire stripping may be similar in effect to Teflon (assuming
there was any real problem there in the first place) - so to be safe, just
don't breathe the smoke.

Cheers,

Dan Schaefer
N235SP