fuses v circuit breakers

[szicree]

C.B.'s are plenty good, just expensive, heavy, and hard to fit into a wiring scheme. By the way, I could turn this around and ask why fuses are good enough for Ford, G.M., Chrysler, Honda, Nissan and Yugo, but not good enough for us?

[Yukon]

I'll say this real slow. Because they are CAR manufacturers........

[Jconard]

I do not have the code in front of me, but generally regulations are not interpreted in such a way as to make them ridiculous.

My instructor (who was active in the local rv community before he died) always said that you had to be able to reach the fuses, and the spares.

From memory, I believe that in the same section is a requirement for adequates source of power for required equipment and radios.

Read together, it seems to mean that you must be able to change them. Plus applying the notion that no rule will be read in a way that makes it a ridiculous, I doubt that the FAA reg is to be read to mean

"You must carry spare fuses, and you must be able to reach them in flight, but it is okay for you to be unable to do anything with them"

Just my amature opinion.

[kevinh]

Originally Posted by Yukon

I'll say this real slow. Because they are CAR manufacturers........

Wow - that was civil.

[Jconard]

Oh, as to source of stuff,

I would call Steinair. Their prices are generally the lowest, but even where they are not, I have found them very helpful. Most who work there are former Northwest airlines mechanics, and several of the guys are engineers and simulator technitions. NWA has more than 20 full motion jet simulators in the Twin Cities, and these guys work to keep them running....they have been very helpful as to my panel.

I bought the "master kit" which had everything I needed. Of course once you learn to love different colored tefzel, you end up buying extra wire for the coolness.

[jcoloccia]

LOL. If an airplane manufacturer jumped off a bridge, would you jump too?

All kidding aside, fuses and breakers both have advantages and disadvantages, and there are good reasons to use both.

If you like the look of a modern panel with banks of pullable circuit breakers and satisfying "clicks", breakers are great. They're also cool when you have something like a trim/flap motor that you want to be able to kill in case of a runaway (if you worry about that sort of thing). They also are well suited for motors because they don't trip as fast as fuses (you can always use a "slo-blow" fuse...there are other types also that work). They're also neat because when they pop, they're easy to reset (why anyone would reset a popped breaker in flight, I'll never know....hey, it's your airplane and your life).

Fuses are the ultimate in reliable circuit protection. There are no contacts to weld shut, no circuitry to drift out of calibration and otherwise no moving parts to fail. They don't have the coolness or convenience factor of a breaker. In general, they trip faster than a properly selected breaker. There is simply no question that for RELIABLE circuit protection, fuses have it all over breakers (planes, cars, boats...I'm not talking exotic applications here). Most definately, they lose on convenience and also you loose the ability to easily disable entire circuits in flight. Why you'd want to do this in a tiny little plane like ours, I don't know, but if you're talking LARGE complicated systems, breakers are pratically required so that you can "tag out" various parts of the system and allow the rest to keep going, or for maintenance.

Breakers work well in homes where the load on a circuit is unknown (i.e. mom's vacuuming the floor while dad's running the hair dryer....whammo, breaker pops). WAY more convenient (and safer) to reset the breaker than replace a fuse. In our airplanes, we know exactly what the loads should be. We'd better since we're sizing our wires for the load and the breaker/fuse for the wire. Unless you have a plug for your hairdryer on the plane, the breaker should never pop unless there's a real fault.

This doesn't really answer your question, I don't think, but there isn't any one answer. Personally, I intend to use fuses practically everywhere except maybe on the flap/trim motor, OV protection and maybe one or two other things I haven't thought of yet. The reasons for me are simple:

1) realiability....the only failure mode of a fuse is to fail OPEN. I'll take it
2) simplicity
3) size and weight
4) cost

Either way, if you do it right both fuses and breakers will provide adequate circuit protection and there are no overwhelming advantages/disadvantges to either in terms of safety.

[mtclay]

Tony,

Check your private messages.

[Yukon]

Part 91 does not regulate aircraft construction. That would be in Part 21, 23 or 25 (from distant memory). If 91 requires replacement fuses be in reach of the pilot, another part certainly requires the fuse holder to be within reach of the pilot. Of course none of this matters in an experimental. If you have a glass cockpit, there is no reg to restrict you from putting your fuses on the back of the firewall, but let common sense be your guide. Unless you have very long arms, I would prefer them to be easily accessable.

Over the years I have reset many breakers (once only) and continued to destination. Alternator Fields in light planes, and in jets lighting cb's trip
fairly often, for no particular reason. Having said that, I think CB's tend to wear out,or otherwise become "soft". I think that is Bob Knuckol's issue with CB's. He feels that fuses are so reliable as to be placed out of reach of the pilot. Not the way I will build my plane, but I sorta see his point.

[Jekyll]

Originally Posted by Yukon

I'll say this real slow. Because they are CAR manufacturers........

My 'trons have no idea they are in an airplane; they can think they are in a car for all I care.

The FAR only requires you to carry spare fuses for those "that are accessable to the pilot in flight". If none are accessable, than you meet the FAR with no spares. There be nothing in my acquaintance that states certain fuses must be accessable in flight.

A properly designed electrical system will meet the FAR's requirements for "an adequate sorce of electrical energy for all installed electrical and radio equipment" with either CBs or fuses.

Jekyll

[Yukon]

Don't you find this sport just a little odd?

Fuses in building were replaced 40 years ago with circuit breakers, because circuit breakers are superior in all respects. I have replaced many fuses in cars, reset many breakers in airplanes.

Dual, self generating mags were considered the standard of the aircraft industry for 70 years. What's this dual Lightspeed craze?

Two plugs per cylinder has been common sense since 1925. Why do alternative guys want one?

Most production GA airplanes have gascolators. Why do we wonder why our fuel pumps fill up with metal shavings?

Design gross weight used to be determined by engineers. Why are the builders allowed to do it now?

Why are we installing plastic engine sumps? I give up!

I'm all for improvement of the art, but I'm seeing alot of change for the sake of change in this sport. Let's keep our eye on the ball. Gravity still hurts.