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Flexible Wire for Pull Out Fuse Tray?

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Valin

Joined: 13 Apr 2010
Posts: 31
Location: Colorado

Posted: Tue Apr 28, 2015 2:50 pm Post subject: Flexible Wire for Pull Out Fuse Tray?

Hello Bob,

 

Thanks again for all your help over the years of our (wife and my) Lancair Legacy project.

 

In our electrical system design, we’ve gone with a pull-out fuse tray that is on the right side of the instrument panel.  It’s about 4 “ tall, 2” wide, 24” long and uses blade fuses that light up when they’ve blown.  All the fuse blocks are easily visible to the pilot when the tray is pulled out.  

 

We chose this solution because of its simplicity and minimum real estate on the Legacy’s small instrument panel.  In its implementation, though, I’m a bit concerned with the fatigue life of the thick wires running to it with the tray being pulled out and in for each flight with before takeoff checks.  The MIL-W-22759 wire in these gauges is fairly stiff…  There are several since the diodes between buses are on the avionics shelf because of fuse tray space limitations.

 

Is there a very flexible 10 and 8 AWG wire that we could use for the connections between our fuse tray and avionics shelf, that can better handle the fuse tray motion/flexing than the MIL-W-22759, and is air worthy?

 

Thanks,

 

Valin Thorn

Lancair Legacy Project

Colorado

  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 29, 2015 11:14 am Post subject: Flexible Wire for Pull Out Fuse Tray?

At 17:48 2015-04-28, you wrote:

Hello Bob,



Thanks again for all your help over the years of 

our (wife and my) Lancair Legacy project.



In our electrical system design, we’ve gone with 

a pull-out fuse tray that is on the right side of 

the instrument panel.  It’s about 4 “ tall, 2” 

wide, 24” long and uses blade fuses that light up 

when they’ve blown.  All the fuse blocks are 

easily visible to the pilot when the tray is pulled out.



We chose this solution because of its simplicity 

and minimum real estate on the Legacy’s small 

instrument panel.  In its implementation, though, 

I’m a bit concerned with the fatigue life of the 

thick wires running to it with the tray being 

pulled out and in for each flight with before 

takeoff checks.  The MIL-W-22759 wire in these 

gauges is fairly stiff…  There are several since 

the diodes between buses are on the avionics 

shelf because of fuse tray space limitations.



Is there a very flexible 10 and 8 AWG wire that 

we could use for the connections between our fuse 

tray and avionics shelf, that can better handle 

the fuse tray motion/flexing than the MIL-W-22759, and is air worthy?

   Check out a big-box store's electrical

   supplies. You can get a chunk of 10-3 drop

   cord (SJ, SJO)and cut away the insulation to

   acquire three, very flexible and robust

   runs of 10AWG wire.



   You won't find 8AWG drop cord but a welding

   shop can sell you 6AWG welding cable that's

   only a little larger than your 8AWG and probably

   more flexible than the 8AWG Tefzel.

   Bob . . .

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jluckey(at)pacbell.net
Guest

Posted: Wed Apr 29, 2015 12:17 pm Post subject: Flexible Wire for Pull Out Fuse Tray?

You can get a chunk of 10-3 drop   cord (SJ, SJO)and cut away the insulation to   acquire three, very flexible and robust   runs of 10AWG wire.

Bob, is that insulation "kosher" with respect to combustion by-products. 



 I thought that was the reason that Tefzel was the recommended wire/insulation type.

-Jeff



  





     On Wednesday, April 29, 2015 12:24 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

  

  



 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>



At 17:48 2015-04-28, you wrote:

Hello Bob,



Thanks again for all your help over the years of 

our (wife and my) Lancair Legacy project.



In our electrical system design, weâ€™ve gone with 

a pull-out fuse tray that is on the right side of 

the instrument panel.  Itâ€™s about 4 â€œ tall, 2â€ 

wide, 24â€ long and uses blade fuses that light up 

when theyâ€™ve blown.  All the fuse blocks are 

easily visible to the pilot when the tray is pulled out.



We chose this solution because of its simplicity 

and minimum real estate on the Legacyâ€™s small 

instrument panel.  In its implementation, though, 

Iâ€™m a bit concerned with the fatigue life of the 

thick wires running to it with the tray being 

pulled out and in for each flight with before 

takeoff checks.  The MIL-W-22759 wire in these 

gauges is fairly stiffâ€¦  There are several since 

the diodes between buses are on the avionics 

shelf because of fuse tray space limitations.



Is there a very flexible 10 and 8 AWG wire that 

we could use for the connections between our fuse 

tray and avionics shelf, that can better handle 

the fuse tray motion/flexing than the MIL-W-22759, and is air worthy?

   Check out a big-box store's electrical

   supplies. You can get a chunk of 10-3 drop

   cord (SJ, SJO)and cut away the insulation to

   acquire three, very flexible and robust

   runs of 10AWG wire.



   You won't find 8AWG drop cord but a welding

   shop can sell you 6AWG welding cable that's

   only a little larger than your 8AWG and probably

   more flexible than the 8AWG Tefzel.





cs.com/Navigator?AeroElectric-List" target="_blank">http://www.matronics.=   --> <a href="http://www.matronics.com/contribution" target=====

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 29, 2015 12:55 pm Post subject: Flexible Wire for Pull Out Fuse Tray?

At 15:16 2015-04-29, you wrote:

You can get a chunk of 10-3 drop

   cord (SJ, SJO)and cut away the insulation to

   acquire three, very flexible and robust

   runs of 10AWG wire.



Bob, is that insulation "kosher" with respect to combustion by-products.



I thought that was the reason that Tefzel was the recommended 

wire/insulation type.



    It depends on who you talk too. There's one well

    meaning and vocal faction out there that thinks

    Tefzel is spawn of the devil . . .



http://tinyurl.com/2f8uz



    After you've spent some time in the test

    lab letting the smoke out of things, you come

    to realize that the flavor of smoke from any

    combustible becomes a rather moot point.



    Yeah, they do flame tests on insulation . . . by

    plying it with a torch! After it appears sufficiently

    antagonized that it should burn, you take away

    the flame. If I recall the reasoning with any

    accuracy, the flaming insulation should not propagate

    along the wire, it should self extinguish in so

    many seconds, it should not drip flaming

    globs of insulation and . . . oh yeah . . .

    should be minimally obnoxious to respiratory

    system . . . the flavor of a fine pipe tobacco

    being a design goal.



    I've been present when wires were burned

    either by accident or test. I've seen and smelled

    lots of smoke . . . and there were no reminders

    of grandpa's favorite pipe.



    Most the flaming materials wienies seem to

    think that there is increased risks for having

    materials that will PROPAGATE or PROMOTE a fire

    from any/un-named source . . . not many pilots I

    know fly around with propane torches. Getting

    a wire lit up by hard faulting to a battery is

    exceedingly problematic unless the insulation is

    VERY flammable . . . but wait, seems like those

    fuses and circuit breakers are supposed to

    keep things from going that far in the first

    place. No . . .?



    Airplanes have been wired with everything

    from cotton covered rubber to super-exotic-

    unobtanium for over a century. Yet in the annals

    of aviation accidents, I'm aware of no incident

    that was blamed on flammability of the insulation.

    There may be some out there but they're a vanishingly

    small proportion of totality of incidents.



    INTEGRITY of insulation, yes. Swissair 111 wiring

    sparked and set the airplane's cabin insulation

    on fire.  Look at the pictures of the 777 that

    belly flopped in SFO. LOTS of stuff throughout

    the cabin burned with some vigor . . . and I

    doubt that anyone was reminded of their grandpa's

    pipe in that incident either.



    If the flaming materials wienies were really

    taking their jobs seriously, then every new

    requirement that strives for happy fires in the

    cabin would have grounded the existing fleet

    until sub-standard materials were replaced.



    Hundreds of thousands of miles of 'sub-standard'

    wire are airborne someplace over the planet

    as we speak . . .



    I suggest that the lowest risk path to personal

    flight is grounded in good FMEA, craftsmanship,

    and plan-b for highest risk failures. If

    you've got serious smoke in the cockpit

    that doesn't quit when you turn of the master

    switch . . .  well . . . the flavor of that

    smoke is the least of your worries. I prefer to

    design for no-fire as opposed to designing for

    friendly fire.



   Bob . . .

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