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In a message dated 10/20/99 11:24:59 AM Eastern Daylight Time, CIC@centurytel.net writes:
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Wire insulation: Lots of discussion about this vis-a-vis the MD-11 crash
off Canada. Maybe tefzel ain't so hot after all? I've got an e-mail
inquiry in to the Belden folks about insulation types, but I'm not convinced
that using all (or mostly, see below) tefzel insulated, milspec wire is
worth the hassle and expense. It's stiff, the insulation cuts rather
easily, it only comes in one color, it's heavy, and it's expensive.
Ordinary PVC-insulated hookup wire (like Belden 8524) passes the VW-1
flammability test, is inexpensive, and comes in about fifty colors
(including stripe combinations).
Besides, how many installations have you seen that use all milspec,
tefzel-insulated wire, then add in RG-58 (which is PVC insulated), then run
the whole bundle through a PVC pipe (which Lancair supplies as conduit
material)??? A better solution would be to use standard aluminum electrical
conduit tubing, and for those who want to stick with teflon, Belden's
83000-series wires have teflon insulation, 600V, 200C rating, and come in 10
stock colors (they meet milspec MIL-W-1687E/4 if anyone has the energy to
dig it out).
Jim Cameron (ex-ES builder, new kit on order for Feb.) >>
Jim,
Please don't take this personal, but I just couldn't let those statements go unchallenged, as It's right in my field and I strongly disagree with most of what you said. PVC wire (including RG58) has been effectively "banned" from aircraft use for many years due to it's flammability and emission of toxic fumes. I've seen some "flame retardant" PVC on the market, but I'm not sure if the toxicity is any better. As for your suggestion that tef-zel cuts easily, compared to what? It's WAY tougher than any of the PVC wire I've ever worked with, and I don't think the weight is much different, although that would of course depend on insulation thickness. It also comes in several colors, although most smaller vendors only stock white. It IS expensive compared to some of the cheap hook-up wire like you mentioned, but if you go to a commercial vendor it's about half what the typical "consumer" oriented vendors charge. I pay about 5 or 6 cents a foot for 20 gage, for example.
As far as I know the jury is still out on the Swissair 111 crash. I haven't been following it real close but if I'm not mistaken, I think most of the focus is on the thermal/acoustic fuselage insulation.
You made the comment that many installers use Tef-Zel wire, and then run PVC coax with it and put in PVC conduit. I agree that is poor practice, but you seem to be making the case for going a step further and use the wrong stuff everywhere, not just some places. Wouldn't it be better to spend a few more dollars and use good coax (RG142) and proper conduit? By the way, I did complain to Lancair a few years ago about that flammable, "conduit" they sell, but as far as I know, they're still using it. You ever do a burn test on that stuff? Sheesh, I wouldn't want that in my car, much less a pressurized airplane at 20,000 feet!
Regarding Teflon wire, it does have it's uses, such as in high-temp areas. I wouldn't use it for general airframe wire, however, as it is not as durable as the tef-zel stuff, and Teflon tends to "flow" when compressed (such as under a clamp or connector backshell). While I'm refering to standard airframe wire as Tef-Zel (a trade name), to be clear, what I really mean is M22759/16-xx-x which is probably the most commonly used kind. M22759/34-xx-x is becoming more popular of late, because it is a little thinner and lighter.
I've seen so many otherwise beautiful airplanes with really horrible and downright dangerous wiring. I guess it's kind of a sore spot with me. It's not that hard to do it right. It just takes the right mind-set (and a little cash for the right materials).
Sorry if I got off on a rant there.
Jim McMillan
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
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