Message-ID: <000501bf1d34$4fc3cc40$2e6b1b3f@oemcomputer>
Reply-To: "dfs" <dfs@gateway.net>
From: "dfs" <dfs@gateway.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: Wire insulation
Date: Sat, 23 Oct 1999 01:54:37 -0700
Mime-Version: 1.0

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Brent is right regarding Teflon insulation being disallowed on aircraft
applications - except that proscription only applies to the primary airframe
wiring. It is allowed within an LRU (Line Replaceable Unit, in Air Force
parlance). I found this out after much kicking and screaming at a system
vendor while pointing to the Specifications for the B-1. I thought it was
clear that Teflon was banned everywhere in the airplane. The spec gurus said
"No, inside a box is OK". So, if you have heard that there is Teflon
insulation in an airplane after all, it can only be inside an enclosed
unit - not in the primary wiring. I still don't like it but, on military (AF
at least) aircraft, it can be found.

I also mentioned earlier that, though we originally wired the B-1 almost
entirely with Kapton wire primarily because it is very thin and light for a
given voltage rating, all subsequent mods require the 22759/xx tefzel. This
was for safety reasons. High voltage, Kapton and moisture don't mix - in
fact, it;s a deadly accident looking for a place to happen. There were
several incidents on the B-1 where a ground crew was washing down the wheel
wells and they experienced what can only be described as an explosion
involving wire bundles when power was re-applied to the aircraft. Of course,
the B-1's primary operating ac voltage is twice the normal (230/400 3-phase)
but it came to light that the Navy had had some of the same problems with
lower voltage aircraft. Their operating environment (salt water) was
probably to blame but they banned Kapton too, if my memory serves.

If the crash aircraft had Kapton wiring, it's probably suspect, but that's
in the hands of the proper authorities and I won't speculate.

As for running the wiring in a PVC conduit, probably not extremely swift,
however, if you have properly protected ALL wire runs in your airplane with
breakers or fuses (remember, the breakers and fuses are there ONLY to
protect the wiring - not the equipment being connected) it should not be a
problem. Still, had I to do it over, I'd use something else - a lightweight
fiberglass tube, layed up on an appropriate form, would probably be best
unless something commercial could be found. Sometimes you think of these
things too late - that's what this forum is for - to keep those who come
after from making the same mistakes.

cheers,

Dan Schaefer


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