On Sunday, October 20, 2013 12:23:18 PM UTC-7, Dave Nadler wrote:
On Sunday, October 20, 2013 1:07:38 PM UTC-4, Darryl Ramm wrote:

Uh? Why are you talking about "thermal trips" and

automatic resetting?



Hi Darryl - I think he's talking about PTCs, which are

appropriate in some situations but not here...

Hi Dave - yes, hopefully common sense would prevent their use. And automatic resetting breakers are also forbidden by CFR 14 23.1357. But part 23 may not apply to a JAR-22 derived type certificate on a glider but its a good place to get input on ways to do things and what an A&P/DAR/FSDO would like to see. Folks really ought to think Klixon type breakers if using a breaker on gliders.

Folks might also want to note the requirement in CFR 14 23.1357 for the fuses to be replaceable in flight if critical and the need to carry spares. So you might be able to argue that some non-critical fuses can be placed behind the panel but others will clearly fail that requirement. I'd not want to argue with the FAA for example that the fuel pump or engine controller fuse holders and replacement fuses in a motorglider don't need to be accessible to the pilot.

Also see FAA AC 43.13 Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair. Chapter 11 (Electrical Systems). Lots of good stuff there that should be read by anybody who is considering messing around with any aircraft wiring, not all of it applies to gliders however. And as promoted before on r.a.s. there is lots of advice on aircraft wiring on this web site. http://www.aeroelectric.com/articles.html (mostly intended for home builders of power aircraft)

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And... if working on any aircraft start with talking with a local A&P (or maybe an EAA homebuilder or similar), if certified they'll need the A&P will need to sign off on what you do (or do it for you), if experiential you want their advice and likely a look over what you are planning to do/have done. There is a lot to gain by actually having somebody look over your shoulder that you can't get off r.a.s.

The most important place for circuit breakers is right at the battery, typically a 5A or 10A breaker mounted on the battery or right next to it that will protect your aircraft/wiring harness from a fire caused by a dead short.. I would use a breaker for that, easy to reset, never missing a replacement fuse etc. and the voltage drop is relatively insignificant for these higher current breakers. That primary circuit protection is in JAR-22 but is unfortunately vague.

What you do downsteam for there is more complex, some avionics/device vendors will spec a slow or some cases fast blow fuse to protect delicate devices, some will say a breaker is OK. Read the documentation. Get advice from somebody experienced with this stuff who can look at exactly what you are doing. Note the FAR and JAR requirements for each "critical"/"saftey of flight" device to have its own separate overload protection, and just good common sense as well.

Darryl