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fuses v circuit breakers

T

tonyjohnson

Well Known Member
Not to rehash what may be an old topic, but I could use some help in the final design of my electrical system. I will be using fuses instead of circuit breakers for most electrical items but I am wondering if there are some items so essential that they should be on circuit breakers.

For those of you who are using fuses, are there any items that you chose to use a circuit breaker instead? Are there some items that you used fuses for that in retrospect you wish you had used a circuit breaker for? GPS, flap motor etc.?
 
The only fuse we used is the 'keep alive' for the radio and dynon ... and we are switching it over to a circuit breaker! If you just jump start the plane it blows every time.
 
n468ac said:
The only fuse we used is the 'keep alive' for the radio and dynon ... and we are switching it over to a circuit breaker! If you just jump start the plane it blows every time.
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??? Jump start the plane?

I used fuses on literally everything with the exception of the alternator field. Absolutely no issues or regrets in almost 1000 hours. I have never had to look at my fuses let alone change one. Nuckolls/AeroElectric Z-11 for the most part. B&C externally regulated alternator.

Build your system correctly and it won't matter what you use.

I should also mention that adding new items (autopilot, XM radio, Garmin 396, etc.) has been at worst trivial, since all I had to do was wire to another fuse terminal on the block. With breakers, I swear I hear builders talking about "piggybacking" on other breakers all the time when they add doodads. The fuse blocks are truly convenient in the context of upgrades. Fuses are cheaper, lighter...where's the down side?!
 
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I fused all except the alternator and trim. Why, fuses: cheaper, easier, lighter and less complex. Fewer possible failure modes. Alternator has CB's for the DC master power and voltage warning light because that's the way the PlanePower drawing showed and I didn't feel like altering that. I went with a 60 amp schottky in lieu of a 60 amp CB or ANL for the main feed. I put a CB in the trim circuit so I could shut off power in the event of a run-away. I considered one for the flaps but in the end, I went with a fuse.

Fuses do provide for easier growth as stated by Dan. Just add the wire to the block and insert the new fuse. Couldn't be easier.

Jekyll
 
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Don't the rules of night flight require a set of spare fuses, within reach of the pilot, and the ability to change those in flight?

Most RV's that use fuses seem to put them in places where they cannot be replaced in flight.
 
It says absolutely nothing about the ability to change fuses in flight. 91.205 merely says that the spare fuses themselves must be accessible to the pilot in flight:

91.205(c)(6) One spare set of fuses, or three spare fuses of each kind required, that are accessible to the pilot in flight.
Click to expand...
 
Jconard said:
Most RV's that use fuses seem to put them in places where they cannot be replaced in flight.
Click to expand...

Actually it's quite easy to place the fuse block in a place that is easy to reach during flight. Mine is on a plate that pivots down in front of the passenger.

I couple of months ago I had a over voltage situation that popped a fuse. The breaker on the panel should have popped but as it turns out the breakers don't always pop at their rated current, like the fuses do. I was in the rain at 1500 feet AGL and was able to replace the fuse by myself. Before I get slammed for replacing an over voltage fuse in flight, the regulator had be going up and down in voltage and it just got too close to the OV limit. I had a pretty good idea that replacing the fuse would have been just fine, and it was.
 
Without it becoming a commercial for a particular company, I would prefer to get all my stuff in one place. Who would you all recommend that carries most of the materials needed to wire my plane?
 
Automotive Fuses

Can somebody explain why Van's, Cessna, Piper, Boeing, Douglas and Lockheed etc. uses circuit breakers, but they aren't good enough for me???

John
 
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? :rolleyes:
 
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.
 
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.
 
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.
 
Part 23

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.
 
Yukon said:
I'll say this real slow. Because they are CAR manufacturers........
Click to expand...

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
 
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Isn't it odd?

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.
 
What about????

Jekyll said:
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
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What about voltage spikes, runaway trims, worn out flap motors, load shedding........you car guys need to adapt to aviation or get back into cars.

Just my humble opinion :)
 
Jorge:

Stein Air, Affordable Panel and B&C all have good stuff. There are differences though such as 1 of them may carry switches with screw-on terminals only while another may cary fast-on style switches. I noticed when sourcing my components that they each carried different size fuse blocks. I chose my fuse block vendor after doing a complete load and system analysis to determine the number of positions I needed for each bus. Finally, most of the basic components come from the same sources so quality will be the same. I built a simple speadsheet that helped me choose based on price when all else seemed equal. I'll just say that one of the vendors was several hundered dollars higher in total cost for the same basic stuff.

Additionally, each have some unique items that you may find interesting. Stein has a really nice EI strip light that seems to be one of the best out there. B & C has some nice gooseneck lights that make great map lights and can double as a dome light (interior light, just wire them to an always-hot bus). Perihelion Designs has some really nice odd-ball items (I should say specialty items) such as a great dimmer switch, schottkys, diodes for isolating an e-bus and heavy cabling. Especially neat are the NASA style switch guards! (look at Paul Dye's panel).

I can understand it may be easier to order from 1 vendor but there are significant benefits and other reasons for shopping around. One last reason to use multiple vendors is the benefit to all by spreading your money around. The greater the number of suppliers for our small field of business, the better. Many of these vendors are just pilots like you and me that took the hobby to the next level. Its good to keep them with us as they are often the innovators that bring good things to us and keep the prices down. Example, do you want to save 5% on the price of a major EFIS? Call the above mentioned vendors and you'll find at least one that will sell you BMA or GRT for less than the manufacturers. We definately need to keep these guys in business for us.

Jekyll
 
BOTH

Some will make a strong case for fuses, and in-fact many have made them main stay of their aircraft electrical wiring schemes with success. Using fuses is not a new idea and has been done in homes and planes for a long time. The modern automotive fuse is better than the old glass ones, so why not. They are light and cheap.

However the CB's have advantages, and those advantages are real and useful. The biggest down side is cost. Propaganda or rhetoric that CB's don't work well or are unreliable is just not true.

Here is my philosophy, use both where they make sense.

USE CB's
Picking the primary items, high load and items you THINK you might like to:
reset in flight
isolate in flight and
know overloaded planned current,​
Put those on CB's,
preferably with pull-able feature.

USE FUSE's
All the minor items use modern blade flat auto fuse. The fuse blocks are light and cheap.

I went with all CB's, about 20 Circuit Breakers, which are my prefrence. I had a bunch of high end mini CB's on hand so it was easy to choose them. If I did not have the CB's on hand I would have no problem replacing all but 3 or 4 of the CB's with fuses. I already have a few in-line fuses.

Items such as the alternator control/regulator, alternator power/output, flap motor and possibly the Nav/Collision/Landing lights I would always use CB's on.
 
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I went with fuses mostly for the sake of simplicity. Regarding safety, nothing in my electrical system is mission critical and I have to agree with Nuckoll's position that trying to troubleshoot an electrical problem in flight by resetting breakers might not be such a great idea. As far as breakers or fuses blowing for no reason, I've gotta disagree. They blow because they're faulty or too much juice is flowing across em. Either way, I'd rather just leave em blown and find a runway.

Regarding the regs, even if you have everything on breakers, lots of equipment is internally fused. Am I supposed to carry a set of nutdrivers and soldering iron too so that I can tear into a honked up transponder while trying to stay right-side-up? I remember my CFI telling me about the spare fuse requirement, but it has always seemed a bit ridiculous to actually be swapping out fuses while in flight.

I remember my very first apartment had a garbage disposal blow its breaker. I pushed it and things worked for a while. My girlfriend, having witnessed this miracle, tried the same fix a couple of days later, only she pushed it several times. She stopped when it started smoking. :eek:
 
Put it where?

George,

My heartburn is not so much the fuse, but where I see people mounting the fuse blocks. If light and cheap are your requirements, I think it is false economy on such an expensive project.
 
Yukon said:
What about voltage spikes, runaway trims, worn out flap motors, load shedding........you car guys need to adapt to aviation or get back into cars.

Just my humble opinion :)
Click to expand...

Yukon: I've been a professional aviation maintenance technician and maintenance manager for 30 years. Been a pilot for 24 years. Never done nothing in cars except to gas them and drive them. Oh, I've changed several fuses over the years but I have always needed to stop, get out and climb, crawl, reach or shimmy to get to the fuse box.

My system is designed to control and mitigate spikes.

I shed load by throwing a single switch to an e-bus or by using the OFF switches. I seem to find my panel festooned with on/off switches.

Runaway trim, read my previous post. I have a CB for my trim.

Worn out flap motor, if it pops either a fuse or a CB, I'm done moving it. Trim to the new configuration and land when practical.

Certified aviation has an incredible inertia resulting from government regulation. It takes incredible energy to change its course. We are freed from this inertia. Each of us is free to accept the inertia or move beyond it.

I for one, am glad I don't have to fly spam any more. I don't see fused aircraft raining from the sky. I do recall a 747 raining down due to a spark in a wire. Mayby a fuse would have failed faster than a CB in that instance and averted the disaster. I don't know one way or the other, just a point to ponder.

If you don't want to use fuses, then by all means, please use CBs but DON'T insult others that have a differing opinion about a viable and proven technique.

Jekyll
 
I get it

Yukon said:
George, My heartburn is not so much the fuse, but where I see people mounting the fuse blocks. If light and cheap are your requirements, I think it is false economy on such an expensive project.
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I don't disagree with that. I have 20 Texas Instrument "Klixon" CB's, mini, light weight, temp compensated blaa blaa. So you see my prefrence is for the CB, but.........

The fuse "phylosopy" is if the fuse blows you don't need or want to reset it necessarily. You will know the device or circuit is not working, but you can live (fly) without it. Why have a CB you can reset or that indicates a trip, although both useful features arguably. I get that.

I get that resetting is nice but may not be needed or desired. It is always at the discretion of the pilot to NOT reset a CB. My CB's will not let you reset a shorted circuit ("Trip?free design").

Also get an indication of the trip is nice and may be one of the better argument for the CB. I want to know if a FUSE blow before taking off again. So unless you check or notice that circuit is not powered the FUSE lets you down a lot in the indication area. The CB is a visual indication as we all know of something not right.

The FUSE may not have as much function, but it works in protecting the wire as well as a CB. The wire protection is the main function, safety of the wiring.

I get it but I choose to go with CB's. However the lower cost and weight for the same level of safety (may be not function) is attractive and understand the draw.
 
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Yukon said:
What about voltage spikes, runaway trims, worn out flap motors, load shedding
Click to expand...
All you're missing is a glitch, and you'd have the entire rougue's gallery of fictional electrical nightmares. :)
 
The requirement for a type certified aircraft to have certain fuses that are accessible in flight is 23.157(d), which states:
14 CFR 23.157(d) said:
If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse must be so located and identified that it can be readily reset or replaced in flight.
Click to expand...
I know that doesn't apply to us, but I thought it was worth mentioning. 91.205 was probably written with that in mind, but who knows?

I did have one experience that leans me a wee bit towards the circuit breaker camp. I had a circuit breaker trip because of a defective indicator lamp in the instrument panel. Somehow, something failed in the bulb itself, resulting in not just a blown lamp (like you'd expect) but a tripped CB as well. I replaced the bulb, reset the CB, and everything was back to normal. The lamp was the green indicator for the right main gear of a regional turboprop. It was popping the Landing Gear Control CB, causing the whole thing to go dark.

Just an anecdote and probably worth what you paid for it, but I think of that experience whenever I come across a discussion like this.


(Standard disclaimer applies, I know RVs aren't retracts, your essential fuses are where you can reach them, etc etc.)
 
Zero Current

Yesterday, I turned off my Master/Alt and Avionics Master (Gelcell back-up).
The wings remained attached and the Prop kept turning.
I have a map, a watch and a Magnetic Compass, and believe I could find a runway and do a flapless, no ASI approach to an acceptable landing...... IN DAY VMC. With that philosphy I used fuses in all but the Alternator field.

On the other hand, if I wanted Full IFR capability I would re-think it all.

Before debating fuses/Cbs, you need to decide what you intend to do with the beast.

It also should be appreciated that Cbs aren't there for repeated resetting. Only ever once. In fact, one maker of Commercial Airliners (the one Americans don't like a whole lot) took all the Cbs out and stuck them in the Avionics Bay for the ground engineers to reset.

Pete.
 
Cost of CB's vs fuses.

I think that if you sum up the costs, the P&B W28 series of breakers ends up being cheaper than fuses on a per-circuit basis. About $2-$3 per circuit, plus the cost of a copper bus bar.

Also, it's possible to make a compact installation in plain view of the pilot. These breakers are mounted into holes on a 3/4" center. When tripped, the breaker shows a white flag, and it's immediately obvious which circuit is affected. Pre-flight checks are possible, compared to hidden fuse blocks.

They can be labelled using 'white-on-clear' label tape.

They do take up panel space. The photo shows 22 CB's taking up 8.25" x 1.5" of panel area.

Vern Little 9A

108_0829_1.jpg

108_0832_1.jpg
 
Auto Parts

If you don't want to use fuses, then by all means, please use CBs but DON'T insult others that have a differing opinion about a viable and proven technique.

My mistake, Jekyll! Your posts kept invoking auto references, so what am I to think? I too am an A&P and used to be an IA, and I suppose thats why some of the posts here drive me just a little nuts sometimes. That doesn't mean I don't learn alot being here, it's just I don't agree with remote fusing in an aircraft.

Since this forum is an information exchange, tell us all now how you preflight your hidden fuse block. If a fuse blew taxiing in, (flaps, landing light, transponder, etc. )can that be easily determined during preflight? Can I assume that everyboby with fuses preflights their remote fuse block, or do they launch like they do in their Subaru and see what works after takeoff?

Sorry Jekyll, I still don't get it!
 
Yukon said:
Since this forum is an information exchange, tell us all now how you preflight your hidden fuse block. If a fuse blew taxiing in, (flaps, landing light, transponder, etc. )can that be easily determined during preflight? Can I assume that everyboby with fuses preflights their remote fuse block, or do they launch like they do in their Subaru and see what works after takeoff?
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Yukon, you raise a very good point. I don't preflight my fuse block. But here's my philosophy on that...and it will probably just come across as rationalization...

My flaps stay down after landing and shut-down. Easier to get off the wing without dinging 'em. One less cycle of the motor which has, according to posts on rv-list and here, not exactly had a stellar service reputation. My flap motor has yet to fail but I figure every cycle saved counts to some degree. Anyway, the first thing I do before starting the plane back up next time is raise the flaps...bam, I just tested my flap circuit.

My trim is usually slightly out-of-center after landing. Until a few months ago, I always centered the trim while taxiing back in. It always drove me nuts seeing those elevator trim tabs hanging down, an obvious sign that the pilot was trimming up for landing. I liked the look of a centered trim tab. And aileron trim...if left trimmed away from center, the spring tension would cause the ailerons to "bank" a bit. So I used to center it all up before shutting down. Now I've started leaving 'em where they're at -- for the very reason that prior to the next flight I have a way to test the circuit.

Boost pump...I use it on every engine start. If the fuse is blown I will know about it before the engine is ever started.

What else is there? Everything else is ON and showing some sort of positive "indication" when powered up. I know pretty much instantly if something is "down." The exception would be my altitude encoder...and if that fails, my GPS will tell me that it failed. My transponder is non-digital (knobs), and while on standby it won't be flashing...but that's the same circuit I wired my encoder to. So if my transponder fuse is blown, the GPS will complain about no encoder online.

My electronic ignition uses a fuse. If that was blown I would know about it during the run-up check.

I'm trying to think of what else there is that wouldn't "rear its head" when the fuse is blown. The cigarette lighter comes to mind, although it's very rare that I use that.

Anyway, that's my rationalization of not needing to "preflight" the fuse block. Since everything has a "display" these days, why bother?
 
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Dan,

I see your point, but there is no limit to that kind of "automotive thinking". "My mags worked when I taxied in, so why do a run up?". "The prop cycled yesterday, so why cycle it today?" "Carb heat really isn't needed very often on a Lycoming, so I skip it in the runup?" "I hardly ever use that pitot heat anyway"? Besides being bad technique, you are not complying with FAR's when you engage in this kind of rationalization.

Year by year it seems this group pulls further from Van's principles because
"we can". I don't like what I see.

Here's my favorite: "I'll up the licensed gross weight in case I get ramp checked, that way I'm legal"

John
 
Yukon said:
"My mags worked when I taxied in, so why do a run up?". "The prop cycled yesterday, so why cycle it today?" "Carb heat really isn't needed very often on a Lycoming, so I skip it in the runup?" "I hardly ever use that pitot heat anyway"? Besides being bad technique, you are not complying with FAR's when you engage in this kind of rationalization.
Click to expand...

Agreed, but now you're talking about discipline rather than a choice of fuses vs. CBs. Those scenarios apply regardless of fuses vs. CBs. Also...just because the pilot has CBs doesn't mean he checked 'em. A bad pilot is a bad pilot regardless of whether he has whiz-bang super circuit gizmos or no circuit protection at all.
 
Rationalization

Just more rationalization. We are talking about "adequate preflight action". Go read it 91.somethingorother......
 
Sometimes it is great to have an option

A buddy on the first flight in his Glasair used too small of a circuit breaker for his flap motor. Upon putting the flaps DOWN the circuit breaker blew because the flaps were being loaded trying to overcome the air loads. Rather than having to abort the flight and head back or continue flying with the higher drag, he simply reset the circuit breaker and the flaps came back UP with no problem and he was able to continue his flight test.

Just a valid point that some things SHOULD have a circuit breaker and not a fuse. Nice to have the option.

Regarding weight, how much are we talking here 1 - 2 lbs difference in circuit breakers and fuses? Come on, you burn that much fuel in taxi, runup and takeoff. Should not even be relevant to the discussion.

I have CB on everything and all my radios, EFIS, GPS etc. also has an inline fuse. So I guess I have both. No problems so far. FWIW :D
 
No, I didn't read much of the previous, but I wouldn't/don't use anything but Potter-Brumfield or similar quality switch-breakers for most applications. Anything else is a waste of panel space and/or a pain in the rear when it opens up. Exceptions are like flaps, and one or two other light loads where I used a breaker and I might "once-in-a-blue-moon" need to isolate and leave the rest of the load energized.

Can't think of anything, other than possibly a 300, 400 amp main battery fuse that might be worthwhile. And I don't have one of those.
 
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I don't have circuit breakers or fuses for my flaps or trim. As long as my right arm works, so do my flaps and trim (even if the battery is dead or missing).
 
Mel Weighs in on Breakers

Come on Mel, wade in here! Panel mounted circuit breakers or firewall mounted fuses???? What's in your plane? What do the feds think about preflights?
 
I have panel mounted CBs for all electrics. That's not to say that I have a problem with fuses. They are fine, but if something "blows", I want it where I can see it.
 
This whole thing about preflighting the fuse block is a bit odd. Does anyone here preflight their propellor bolts for torque? How about removing the cowl before each flight to check for leaks, loose bolts, hoses etc? Certainly more important than a blown fuse, no?

Dan's right on the money here...preflight in terms of function is the right way to do it.

I like a spirited argument as much as the next guy, Yukon, but if you're gonna beat people up over preferring fuses, possibly you should offer up exactly why CB are better...at least something better than "it's automotive technology" which doesn't mean diddly and is also untrue. It is true that they both have advantages and disadvantages, and it is true that CB's are more convenient, and it is true that fuses are more reliable. It is also true that both are perfectly suitable for the task at hand.
 
?????????????

John, I've told you everything I know about circuit breakers. Don't have much else to add.
 
hecilopter said:
A buddy on the first flight in his Glasair used too small of a circuit breaker for his flap motor. Upon putting the flaps DOWN the circuit breaker blew because the flaps were being loaded trying to overcome the air loads. Rather than having to abort the flight and head back or continue flying with the higher drag, he simply reset the circuit breaker and the flaps came back UP with no problem and he was able to continue his flight test.
Click to expand...

It is nice to have an option, but in the case you describe, isn't the breaker likely to pop when he lowers the flaps for landing. Seems to me it might have been wise to abort the flight while the flaps were in a landing (or close to it) configuration, rather than take a chance on a new and bigger problem at his destination.
 
Preflighting fuses

Blade style (ATO/ATC) fuses that light an LED when blown are available. This would make make the the preflight of the fuseblocks easy, assuming that the fuse block(s) are not buried too deep such between the panel and subpanel.
 
I have fuses for everything except the alternator field and the electric trim system.

This past weekend I fired up to go to a fly-in breakfast but had no alternator output. After decowling and finding no problem I then cycled the alternator field breaker (it was in the normal position) which fixed the problem. So I have about 15 fuses with no problems in seven years and 2 breakers with a 50 percent problem rate.
 
To add a third alternative, what about switch-breakers? I just feel that if you can eliminate running wires back and forth between breakers or fuses, you simplify the installation reducing the chance of making mistakes.
 
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As a professional wireman, I am going with fuses.

Bottom line, overcurrent protection devices are overcurrent protection devices. Select between the two for functionality and what you want to do with them.

For instance, the alternator field will be on a circuit breaker so I can recycle it if need be. The avionics will be on fuses because I have no intention of restoring power while airborne if it should blow. That is asking for trouble.

When an overcurrent protection device trips, it is either because of overcurrent tot he device or a ground fault. Odds are, it is a ground fault because the airplane (hopefully) was planned out ahead of time for max full load current on all the circuits.

If it is a ground fault, I am not going to let it fault again. That could start a fire or fill the cabin with smoke. I don't like the sounds of those choices.

My $0.02 cents

:cool: CJ
 
Yukon said:
Dan,

I see your point, but there is no limit to that kind of "automotive thinking". "My mags worked when I taxied in, so why do a run up?". "The prop cycled yesterday, so why cycle it today?" "Carb heat really isn't needed very often on a Lycoming, so I skip it in the runup?" "I hardly ever use that pitot heat anyway"? Besides being bad technique, you are not complying with FAR's when you engage in this kind of rationalization.
John
Click to expand...

Yukon,

I think you misinterpreted what Dan was saying and incorrectly accused him of being cavalier and/or 'rationalizing'.

He was NOT suggesting that 'since it worked yesterday I don't have to preflight it today'. Quite the opposite. He essentially said 'if I didn't recenter my trim or raise my flaps yesterday, then I'll have to do so before flying today, thus forcing a check of the fuses for those items.' In other words, if the thing the fuse is protecting works, then the fuse is fine.

From what I've heard about Dan, I'd think he'd be one of the last people to habitually skip preflight items.

-mdr
 
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