I'm getting near the point of adding the electrical system to the 601XL I'm building. I would be interested to hear some commentary on the various forms of circuit protection which can be used. I've identified three candidates (but there may be others): fuses, circuit breakers, and the so-called self-resetting fuses (see page 71 in the October Plane and Pilot for a description).

My own thinking is that the self-resetting fuses are cheap enough by themselves, but by the time I put them in some sort of protective housing, and add associated circuit elements, the price approaches that of circuit breakers. Plus, it requires extra fabrication and work. They also don't have a lengthy track record in aircraft applications.

Circuit breakers have a higher initial cost, but don't require spares (compared to fuses). They also weigh more than fuses.

Fuses appear to be the cheapest and lightest approach, but they require carrying spares. From a resale point of view, they also don't have the "pizzaz" of the other two approaches.

I suspect this exchange will be equally applicable to the 701, 750, 801, etc etc. I'll ignite the potential for controiversy by saying that I'm leaning slightly in the direction of fuses, although that has changed almost on a daily basis.

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Jim,

i agree with your concerns on resetable breakers but, in general aviation almost all breakers are resetable. I understand your concern with reseting with out adressing the problem but in the years of working on aircraft electrical systems that dosent happin (pilot just comes in and says theres a poped breaker) and I'm sure that you wouldent do it with your understanding of the concequence. There are some benifits that come with resetable breakers, you dont have to hunt for the fuse, its great for trouble shooting shorts in lighting circuts (immagine a dead short in your nav lights where do you start left wing or the right do u dissconect power one lamp at a time if so that will cost u time and fuses, and it would be time consuming to ring out the wires for each lamp.....so whats a A&P to do the solution was handed down to me from an older hand and its quite simple reset the breaker and apply power while you have helpers watching the lights the nav lamps that momentarly flash on before the breaker trips are good circuits the one that dosent flash is your short and now u have a starting point) the same could be done with fuses but with an extra step or two. Another point is a poped breaker is very easy to see unlike fuses so knowing and adjusting your flight sooner rather than later could help in certan situations, like loosing your alternator poped breaker would let you know before a low volt lamp, plus any electric gauge like a DG or T&B will show a little red flag but almost every time a pilot catches it by the poped breaker. I personaly do not like to use fuses on any thing other than live circuts like electric clocks etc... one last thing and this i can say for sure you will have electrical problems of one kind or another and from my perspective as a mechanic its much easyer with resetable breakers than with fuses. Just my .02

p.s. the breaker/fuse dose protect the wire the wire is sized to the load.

Dave

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