nuckolls.bob(at)aeroelect
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 Posted: Sun Oct 12, 2014 12:00 pm Post subject: Should a tripped circuit breaker be reset in flight? |
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Bill "happily flying with a fully equipped kitchen and sink" Watson
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.
Are there fuses that could be popped and go unnoticed during preflight? I.e. is there potential for latent failure that goes unnoticed beyond preflight?
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.
Bill, Thanks for sharing your observations and deductions from lessons learned. I am curious as to your load distribution configuration that drove the 'fuse pulling' incident. Z-14 offers some pretty robust engine driven power sourcing supported by two batteries. What are your battery sizes and which one is 'critical'?
I've always encouraged builders not to revert to circuit breakers as either the normal on/off ops of an accessory (like the breaker-switches in Bonanzas and Barons), or as a prophylactic against an FMEA deduced situation requiring shutdown of select appliances.
If there's ever a reason to shut a thing off, providing a switch to do the job makes the most sense. Putting an crew-operable breaker on the panel for that purpose MOVES a chunk of your bus structure onto the panel. An attractive feature of the fuse-blocks is organization of the bus structure in tidy, off-panel chunks.
The notion of adding switch based on an FMEA-driven requirement seems elegant way to go while keeping distribution busses off the panel.
Yeah, those pesky strobes . . . Gray beards here on the List will recall a rash of incidents cited by readers experiencing one or more failures of switches on their strobe systems.
http://tinyurl.com/2a2qqp
There was also a rash of failed fast-on terminals with the predominant failure being an under crimped wire.
Seems that many of the modern strobes use constant power energy sources to the tubes. I.e., while 'rated' at 7-8 amps or so at 14.5 volts, they would draw half again more during battery-only and during cranking transients. So strobes that are left ON to warn outsiders of a 'powerd- up' aircraft tend to stress the supply feeder hardware more than the legacy strobes which in fact, would draw less current at lower voltages.
No doubt, advancements in LED offerings will make even this little design quirk a thing of the past . . .
Bob . . . [quote][b]
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