Today's Message Index:
----------------------
1. 09:58 AM - PVC Conduit in Certificated Aircraft (Jeff Luckey)
2. 10:08 AM - Re: PVC Conduit in Certificated Aircraft (Jared Yates)
3. 02:09 PM - Re: PVC Conduit in Certificated Aircraft (Charlie England)
4. 06:24 PM - Re: Re: OVM14 MkIII, rev P1 (Robert L. Nuckolls, III)
5. 06:32 PM - Re: PVC Conduit in Certificated Aircraft (Robert L. Nuckolls, III)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | PVC Conduit in Certificated Aircraft |
Does anyone know if PVC can be used for a wiring conduit in Certificated ai
rcraft?
It is my understanding that the reason we use Tefzel wire in aircraft is to
minimize the toxic gasses given-off from burning insulation.=C2- The mor
e common (and cheaper) automotive-type wire is a no-no because its insulati
on is PVC-based and its fumes are very toxic.
So I was surprised to hear an A&P suggest a PVC conduit in a Certified airf
rame.=C2-
TIA
-Jeff
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: PVC Conduit in Certificated Aircraft |
I'd say the answer to your question depends on the IA who is going to be
signing off the Annual, but may I propose that if you're going to shop in
the plumbing department, I like Pex better than PVC.
On Sat, Sep 30, 2023 at 1:03=AFPM Jeff Luckey <jluckey@pacbell.net> w
rote:
> Does anyone know if PVC can be used for a wiring conduit in Certificated
> aircraft?
>
> It is my understanding that the reason we use Tefzel wire in aircraft is
> to minimize the toxic gasses given-off from burning insulation. The more
> common (and cheaper) automotive-type wire is a no-no because its insulati
on
> is PVC-based and its fumes are very toxic.
>
> So I was surprised to hear an A&P suggest a PVC conduit in a Certified
> airframe.
>
>
> TIA
>
>
> -Jeff
>
>
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: PVC Conduit in Certificated Aircraft |
On 9/30/2023 11:57 AM, Jeff Luckey wrote:
> Does anyone know if PVC can be used for a wiring conduit in
> Certificated aircraft?
>
> It is my understanding that the reason we use Tefzel wire in aircraft
> is to minimize the toxic gasses given-off from burning insulation.
> The more common (and cheaper) automotive-type wire is a no-no because
> its insulation is PVC-based and its fumes are very toxic.
>
> So I was surprised to hear an A&P suggest a PVC conduit in a Certified
> airframe.
>
>
> TIA
>
>
> -Jeff
>
PVC has a much lower temperature rating than Tefzel. IIRC, it's also a
bit more vulnerable to moisture migration through it to the copper. I
believe that all the insulations, including Tefzel, emit nasty gases
when they burn.
--
This email has been checked for viruses by Avast antivirus software.
www.avast.com
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: OVM14 MkIII, rev P1 |
At 12:31 PM 9/28/2023, you wrote:
>
>A wise man once said, "That popped circuit breaker just prevented a fire.
>Do you want to reset it and give the fire a second chance?"
There's a not so subtle difference in stresses
that pop breakers. Assuming the breaker was indeed
opened by an ov event, then the breaker was responding
to an artificially created, dead-short by means of
an electronic short to ground. The breaker opens in
typically 15-30 milliseconds.
The potentially hazardous fault is generally
a soft fault that takes a long time to open
the breaker if ever.
Recall the story about the Model 99 Beech
on short final to runway in New Mexico suddenly
experiencing total disconnect between the wheel
and elevators. Seem a 6AWG feeder to windshield
de-ice system (protected by a 60A breaker) had
be badly positioned during maintenance under
the copilot's floorboards. It was rubbing against
the elevator cable for many weeks after the
maintenance action. Insulation eventually wore
away and the cable began to arc against the
exposed wire. No smoke, no fire, no visible
anomalies in the cockpit. But the relative
robustness of copper vs. steel was demonstrated
when the control cable finally parted.
The ship was successfully landed using elevator
trim. Damage to the wire itself was minimal . . .
stainless steel control cable not so fortunate.
That scenario offered a great deal more potential
for causing a fire WITHOUT opening a breaker
than a hard fault that would open a breaker
almost instantly.
The rational for specifying a high quality,
aircraft friendly breaker as upstream CBOVM
systems was allow, nay encourage a reset-it-once
action by the pilot. This allows the pilot
to deduce if the ov trip was a nuisance event
or a real one. If it were a nuisance event,
the breaker would stay in, the alternator would
come back on line and the bus voltage would be
normal.
Should this prove to be a repeating even over
a period of time, an investigation into root
cause is indicted . . . and not easy. I've had
occasion to chase down two such events; one on
a Europa and the other on a Beechjet. The first
one was fairly easy, the last one cost mucho
Kilobux before root cause was located and
remedied. After more than a month of diligent
attention from field service, I instrumented
the fault detection circuitry in the generator
control unit and conducted a bunch of tests
that eventually pointed to the ground fault
transformer as the source of the antagonistic
signal. The signal cropped up on this aging
airplane as ever increasing ground path
resistance rose with time. Built a sheet metal
bracket to relocate the transformer 1 inch further
away and the noise disappeared!
The point being that the first trip signals
potential for an enduring problem in which case,
resetting the breaker simply forces the OV
management system to do an encore and
the breaker quickly reopens. Once determined that
multiple resets in support of testing does
not constitute a hazard, multiple 'trips'
while probing the system is not contraindicated.
This was a particularly miserable job . . .
had to bring the airplane into a hangar to
configure various tests and then taxi it out
to the compass rose about 1/2 mile way
in freezing rain to conduct the tests!
>Adding a 50 cent TO-92 part and a LED could save much time
>troubleshooting the cause of the tripped breaker.
>More importantly, if the LED is illuminated, the pilot will know
>that it is safe to reset the breaker.
>If the LED is off, then it is best to wait until safely on the
>ground before resetting the breaker.
>The suggested LED has a narrow beam angle and should be aimed toward
>the pilot's face.
>I modified Bob N's circuit below by adding an SCR and external LED
>circuit. And thanks Eric for your help.
There's nothing bad about the proposed ov
trip memory light but I suggest it has
no practical value. 99.99% of all breakers
and fuses go to the bone yard never having been
called upon to prevent a fault from maturing to
a hazardous condition. Even the ATP category
operations manuals allow for reset-one-time for critical
systems. One is not flirting with disaster
by asking the system to confirm a condition while
observing results of a well crafted and monitored
test. I'll be we 'tripped' that Beechjet 20+ times
before we found the problem.
I can assure you that when and if that breaker
opens, lo volts warning will tell you about
it very quickly and the fault is almost certainly
a perceived ov condition. The current re-design (longer
and self re-setting time delay) promises
to reduce probably of nuisance trips
to 10 to the minus 9 probability numbers.
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: PVC Conduit in Certificated Aircraft |
At 11:57 AM 9/30/2023, you wrote:
>Does anyone know if PVC can be used for a wiring conduit in
>Certificated aircraft?
A TC aircraft left the factory configured
per approved drawings. Substituting any
part not on that drawing requires an
approval via one-time field approval (Form 337)
or an STC.
I can't imagine any licensed technician
attempting to 'sell' such a deviation
to the local FSDO.
What kind of 'mod' are we talking about?
If the wires were not part of the original
TC then one is advised to rely on
legacy practices when submitting a Form 337.
To be sure, PVC plumbing would not fall in that category.
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|