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Mauledriver(at)nc.rr.com
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 Posted: Sat Oct 11, 2014 8:25 am Post subject: Should a tripped circuit breaker be reset in flight? |
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| Quote: | My own preference for not re-setting breakers has
more to do with builder competence in crafting
and pilot competence in carry out a Plan-B. These
are exercises in pre-incident planning that go
to making breaker resets or fuse replacements
irrelevant.
This isn't about fires, it's about avoiding that
deer-in-the-headlights look that overcomes too
many of our span-can driving brothers. Incidents
described in detail over decades of what I've called the
"Dark n Stormy Night" stories popular with the
journals . . . Sport Aviation not withstanding |
FWIW, I tried to follow this thinking in my plane. I ended up with 4 breakers and 2 fuse panels in my Z-14).
Breakers 1&2 = for (2) LRC3 Voltage Regulators per installation instructions.
Breaker 3 = flap motor (my thinking was that flap deployment at highspeeds could/might pop the breaker and I'd like to be able to reset. Casual testing indicated that the motor just 'stalls' or 'slips' but never pops the breaker)
Breaker 4 = Autopilot because the TruTrak unit doesn't have an on/off switch. Intent is to use it as an emergency on/off switch.
In retrospect after 3 years and 500 hours , Breaker 3 was a mistake and is not needed, a fuse for wire protection would do. Breaker 4 still makes sense to me though such an emergency has never been encountered.
However I wish I had either installed 3 additional breakers or at least on/off switches for my (3) GRT EFIS screens. These devices lack on/off switches and are always-on when main power is on. That is how I normally operate. But they are major consumers of electrons and any load shedding exercise would benefit from being able to shut down 1 or 2 of them. With 2 batteries and 2 alternators, all scenarios that involve loss of a single battery or alternator allow me to complete the flight without a problem with all (3) on. But starting a cold engine, on a cold day, with the critical battery drawn down (the one without the (3) EFISs) can be impossible unless the (3) EFISs are taken off line. It's happened and it's required pulling their fuses.
If I maintain and manage my batteries properly, this should never be a problem; but I didn't and it was. On the other hand it's just an on-the-ground non-emergency situation.
In the end, only the (2) breakers for the LRC voltage controllers are needed. I would like all my avionics to have an on/off capability. For those devices that don't (AP and the 3 EFISs), it seems that breakers can serve as infrequently used on/off switches.
Bill "happily flying with a fully equipped kitchen and sink" Watson
[quote] Addendum: One other thing that breakers can do for you is to visually indicate what circuit popped. LED equipped blade fuses can do the same and do it quite well. My fuse panels are installed in the passenger seat foot well and have transparent panels. While not easily reached by the pilot in flight, they are easily visible. Combined with a panel diagram (or transparent panel labeling) it is easy to see what fuse is popped.
The only fuse that ever popped in flight was for the strobe unit. The fix was to replace the unit with one that didn't require a power run from the rear mounted battery, forward to the on/off switch, and back to the rear mounted strobe unit. Now there is an unreachable inline fuse between the battery and the strobe unit. The on/off switch controls the unit via some sort of relay.[b]
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Mon Oct 13, 2014 7:21 am Post subject: Re: Should a tripped circuit breaker be reset in flight? |
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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.
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.
3) Switch-Breaker combos save weight and panel space. These SBs have become much better, smaller and cheaper than the early ones.
4) New approaches like solid state resettables certainly have their place.
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.
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.
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?
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckolls.bob(at)aeroelect
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| Posted: Mon Oct 13, 2014 10:38 am Post subject: Should a tripped circuit breaker be reset in flight? |
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At 12:01 2014-10-13, you wrote:
| Quote: | | Respectfully, your dictate of placement of "minimum cost" above "minimum complexity" and "minimum weight" is purely opinion. |
No problem . . . order your design goals as they
suit your wishes . . . but DO have design goals
crafted with argument that makes sense to you.
As a general rule, cost and complexity go hand-in-hand
a lower cost design is generally less complex. Furhter,
costs should be global and embrace cost of ownership.
In the electronics business, a great many parts are tiny,
exceedingly inexpensive and reliable. So cost and
complexity often swap priorities. It's the project
manager's call . . .
Bob . . . [quote][b]
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