fuses v circuit breakers

[Yukon]

Originally Posted by Jekyll

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

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

[Jekyll]

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

[gmcjetpilot]

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.

[szicree]

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.

[Yukon]

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.

[Jekyll]

Originally Posted by Yukon

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

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

[gmcjetpilot]

Originally Posted by Yukon

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.

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.

[sprucemoose]

Originally Posted by Yukon

What about voltage spikes, runaway trims, worn out flap motors, load shedding

All you're missing is a glitch, and you'd have the entire rougue's gallery of fictional electrical nightmares.

[Joey]

The requirement for a type certified aircraft to have certain fuses that are accessible in flight is 23.157(d), which states:

Originally Posted by 14 CFR 23.157(d)

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.

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.)

[fodrv7]

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.