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Switch-Breakers

 
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neal.george(at)gmail.com
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PostPosted: Fri Jan 06, 2023 8:43 am    Post subject: Switch-Breakers Reply with quote

Bob -
What are your thoughts on using switch-breakers for items that are switched frequently, such as landing lights?

I’m under the impression that they should be reserved for occasional use items, such as Pitot Heat.

Neal


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nuckolls.bob(at)aeroelect
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PostPosted: Fri Jan 06, 2023 11:41 am    Post subject: Switch-Breakers Reply with quote

At 10:42 AM 1/6/2023, you wrote:
--> AeroElectric-List message posted by: Neal George <neal.george(at)gmail.com>

Bob -
What are your thoughts on using switch-breakers for items that are switched frequently, such as landing lights?

I’m under the impression that they should be reserved for occasional use items, such as Pitot Heat.


There was a HUGE kerfuffle at Beech during my tenure
there concerning failures of W31 series switch-breakers
in Bonanzas and Barons. These ships used W31 switch
breakers for ALL of pilot operated switches.

It seems that SOMETIME during the Beech incorporation
of these breakers, a change was made that removed
a tiny bit of insulating material from under a
spring.

This was a new layer of 'swiss cheese' in the
potential for generating a hazardous condition.
Here are documents I've saved from the work
product I generated for the failure investigation.

https://tinyurl.com/2zttqpqt

I thought I had a copy of the failure analysis
narrative but that seems not to be in the library.
Nonetheless, it seems that failure of all the jumper
'cable' strands preceded loading the spring with
the current being carried in the switch. For light
loads, this didn't seem to generate an alarming
event. ONE of these switches in the Bonanza carried
prop de-ice current. This switch would not be a
high duty cycle device . . . none the less, one
fielded aircraft suffered a failure of jumper
strands followed by a catastrophic heating event
in the spring that resulted in much smoke and
bad smells in the cockpit.

So . . . lots of slices of cheese had to line up
to bring this difficulty to the forefront. But given
that there were probably 80,000 switches out there
in Beech products (Not to mention Cessnas too), This
was not a trivial concern . . . ESPECIALLY since
the existence of the insulator could not be
verified by inspection.

So, the short answer to your question is: "Probably
no big deal. All new switches have the insulator."

HOWEVER, keep in mind that when the pilot control
device is combined with the fault protection for that
branch, ship's BUS structure is extended to the
hot side of each control . . . not unlike the special
hat dance we do for the 5A crowbar breaker in fuseblock
fitted airplanes.




Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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Ceengland



Joined: 11 Oct 2020
Posts: 391
Location: MS

PostPosted: Fri Jan 06, 2023 11:57 am    Post subject: Switch-Breakers Reply with quote

On Fri, Jan 6, 2023 at 1:44 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 10:42 AM 1/6/2023, you wrote:
--> AeroElectric-List message posted by: Neal George <neal.george(at)gmail.com (neal.george(at)gmail.com)>

Bob -
What are your thoughts on using switch-breakers for items that are switched frequently, such as landing lights?

I’m under the impression that they should be reserved for occasional use items, such as Pitot Heat.


  There was a HUGE kerfuffle at Beech during my tenure
  there concerning failures of W31 series switch-breakers
  in Bonanzas and Barons. These ships used W31 switch
  breakers for ALL of pilot operated switches.

  It seems that SOMETIME during the Beech incorporation
  of these breakers, a change was made that removed
  a tiny bit of insulating material from under a
  spring.

  This was a new layer of 'swiss cheese' in the
  potential for generating a hazardous condition.
  Here are documents I've saved from the work
  product I generated for the failure investigation.

https://tinyurl.com/2zttqpqt

  I thought I had a copy of the failure analysis
  narrative but that seems not to be in the library.
  Nonetheless, it seems that failure of all the jumper
  'cable' strands preceded loading the spring with
  the current being carried in the switch. For light
  loads, this didn't seem to generate an alarming
  event. ONE of these switches in the Bonanza carried
  prop de-ice current. This switch would not be a
  high duty cycle device . . . none the less, one
  fielded aircraft suffered a failure of jumper
  strands followed by a catastrophic heating event
  in the spring that resulted in much smoke and
  bad smells in the cockpit.

  So . . . lots of slices of cheese had to line up
  to bring this difficulty to the forefront. But given
  that there were probably 80,000 switches out there
  in Beech products (Not to mention Cessnas too), This
  was not a trivial concern . . . ESPECIALLY since
  the existence of the insulator could not be
  verified by inspection.

  So, the short answer to your question is: "Probably
  no big deal. All new switches have the insulator."

  HOWEVER, keep in mind that when the pilot control
  device is combined with the fault protection for that
  branch, ship's BUS structure is extended to the
  hot side of each control . . . not unlike the special
  hat dance we do for the 5A crowbar breaker in fuseblock
  fitted airplanes.

 


  Bob . . .

Not to mention the fact that two or three of them will pay for just about all the fuseblocks & fuses (and maybe some of the wire) we'd need to wire a decent panel...
Charlie


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nuckolls.bob(at)aeroelect
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PostPosted: Fri Jan 06, 2023 12:42 pm    Post subject: Switch-Breakers Reply with quote

Quote:

Not to mention the fact that two or three of them will pay for just about all the fuseblocks & fuses (and maybe some of the wire) we'd need to wire a decent panel...

Charlie

And there IS that!


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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neal.george(at)gmail.com
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PostPosted: Fri Jan 06, 2023 1:06 pm    Post subject: Switch-Breakers Reply with quote

Thanks Gentlemen –
I don’t disagree, but since I’m refitting a Bonanza, I don’t think I can go quite that far…


Neal George


Quote:


Not to mention the fact that two or three of them will pay for just about all the fuseblocks & fuses (and maybe some of the wire) we'd need to wire a decent panel...

Charlie


And there IS that!

Bob . . .

  Un impeachable logic: George Carlin asked, "If black boxes
  survive crashes, why don't they make the whole airplane
out of that stuff?"


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nuckolls.bob(at)aeroelect
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PostPosted: Fri Jan 06, 2023 3:54 pm    Post subject: Switch-Breakers Reply with quote

At 03:06 PM 1/6/2023, you wrote:

Quote:
Thanks Gentlemen –

I don't disagree, but since I'm refitting a Bonanza, I don't
think I can go quite that far…

Hmmmm . . . yeah . . . that T/C parts list
can be a real drag.


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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