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kenryan
Joined: 20 Oct 2009
Posts: 426
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 Posted: Mon Oct 13, 2014 9:03 am Post subject: Should a tripped circuit breaker be reset in flight? |
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Respectfully, your dictate of placement of "minimum cost" above "minimum complexity" and "minimum weight" is purely opinion.
On Mon, Oct 13, 2014 at 8:30 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | There has been some remarkably good discussion on this subject and I want to add my two cents:
1) Breakers themselves fail or degrade. Abused breakers are difficult to detect. Resetting them after they
cool down may be possible. But diagnosis should be a ground-repair issue. Remember to Fly the Airplane.
That's a pretty broad brush . . . SOME breakers are less robust than we might like for use in an extra-ordinarily abusive environment. Consider the inner monkey-motion and parts count of the switch-breaker (on left) and the commercial, off-the shelf appliance breaker on the right . . . with the military qualified device in the center that is RATED and TESTED for thousands of high-fault current trips without degradation of performance. I've never encountered a pre-mature failure in this style breaker when used solely as a circuit protective device and not a crew-operated power control.
[img]cid:.0[/img]
2) The classic "breaker for every wire" seems old fashioned and indeed breakers sometimes
pop in commercial a/c and nobody notices. An LED warning on every breaker seems to be a great idea.
Three points to ponder here. Legacy design goals call limiting failure effects to one system only. It's generally not a good thing to have one failure take down multiple appliances. Hence, one protective device per feeder.
If a protective device operates then some system is off line as a result. If nobody notices, then that appliance is not being used. As soon as the crew expects that appliance to be available, the popped breaker will, no doubt, be noticed . . . whereupon Plan-B for that failure will be implemented.
Adding indicator lights to breaker/fuses only complicates the monkey-motion built into the device. It does not reduce risks to comfortable termination of flight. It might be a troubleshooting aid . . . but then . . . you already know that appliance is inop or you will know before next flight . . . it's on your preflight checklist . . . right?
3) Switch-Breaker combos save weight and panel space. These SBs have become much better,
smaller and cheaper than the early ones.
. . . but still MUCH more expensive than a fuse and they FORCE a modification of architecture to move a portion of the ship's bus structure onto the panel.
4) New approaches like solid state resettables certainly have their place.
But what is the return on investment? If you're not going to reset breakers or replace fuses in flight . . . what is the value of incorporating a 'more modern' approach to hardware that is more convenient to reset? 5) If you don't have to change a fuse during flight, a fuse works well. This
includes, wig-wags, entertainment systems, seat heaters, baggage compartment lights,
convenience lights, rear intercoms, and others.
Under what conditions would it EVER be necessary/useful/ prudent to replace a fuse in flight? Are there design goals to exercise that would eliminate any such condition?
6) Inherently Safe Buses are low-current or current-limited buses where no fuse is
required because a dead short will not generate enough power to ignite anything.
Worth considering in this low-current world of Cmos, Fet gates and LEDs.
Yes, feeders current limited at the bus can be considered intrinsically immune to damage as a consequence of a faulted wire. I've encountered perhaps a dozen such opportunities in my lifetime.
7) A design goal might be to eliminate the breaker panel by employing a variety
of other circuit protection methods. Are there some breakers that never pop? Why
have them?
Exactly. This question prompted an essay published in Sport Aviation 21 years ago: http://tinyurl.com/o9joztv The decision process for circuit protective philosophy has almost nothing to do with convenience or the performance issues unique to devices being considered. To be sure, devices like this http://tinyurl.com/oka6z2a may offer some unique opportunities for adding some appliance to an airplane but in general, a clean piece of paper design should strive for minimum risk, minimum cost, minimum complexity, minimum weight in that order of prominence.
[img]cid:.1[/img]
. . . at the present time, I'm unable to suggest a superior alternative to the rudimentary fuse for keeping all the smoke inside your wires . . .
Bob . . .
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bob.verwey(at)gmail.com
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| Posted: Mon Oct 20, 2014 9:36 pm Post subject: Should a tripped circuit breaker be reset in flight? |
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Guys this has been a great thread and I learned a lot! Did'nt even know some of this stuff existed!
Best...
Bob Verwey
On 21 October 2014 00:25, Lyle Peterson <lyleap(at)centurylink.net (lyleap(at)centurylink.net)> wrote:
[quote] Acronyms suck!
On 10/20/2014 5:02 PM, Robert L. Nuckolls, III wrote:
| Quote: | At 16:35 2014-10-20, you wrote:
| Quote: | What does... CFCTOF=0 mean?
Bevan |
Critical For Comfortable Termination Of Flight.
Includes things like wings, fuel lines, propellers
etc. It can also include fundamental navigation,
communication and cockpit illumination. Then there
are things like providing independent sources of
power for dual ignition systems, etc.
A CFCTOF factor of zero means you could launch
into the blue with comfort knowing the device has
no influence on your comfort level. A factor
of 1 suggests that the appliance is worthy of
careful thought as to what your plan-of-action
will be if the critter rolls TU.
Bob . . . --
Lyle
Sent from my Gateway E4610D desktop
ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
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