Circuit breaker vs fuse in critical circuits

[Avanza]

A standard circuit breaker as a Tyco W58 series, is constructed for >1000 cycles at 200 % of rated load.
W58 Series is UL 1077 Recognized as Supplementary Protector.
These single pole breakers tripping mechanism is made of a bi-metallic mechanism that trips the electric switch.
Breaker will continuously carry 100% of rated load. It may trip between 101% and 145% of rated load, but must trip at 145% at 25°C.
They are used to protect the wire to the equipment from short circuit and overload.
They are used in many aircraft and works well for most equipment.
However when it comes to electric circuits that are critical, for example power to electronic ignition and dual electric fuel
pumps I think it´s important to consider the use of a fuse.
A slow acting fuse behaves like a circuit breaker in that it will trip at a short or an overload and it will protect the wire as a circuit breaker would do.
The difference is that it is less complicated in it´s construction and the risk of malfunction is smaller.
A power wire going to a critical component need some consideration on it´s mechanical strength and how it´s routed and secured.
It should not only carry the load (amp), it needs to be rigid enough to withstand vibration and mechanical loads.
One can use a braided wire to get a stronger wire or one can use a wire protecting sleeve, this will have the benefit of making it more visibel in the installation.
If using a fuse, the fuse holder should be of good quality, that will protect the fuse from water or contamination.
Please follow the manufacturers installation instructions how to provide a safe power supply.

Good luck

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[Walt]

My thoughts:
I toss tons of Tyco breaker/switches in the scrap bin, worthless POS.
Fuses, ok for lights and misc stuff but not for the really 'important' items.
Klixon breakers and high-quality switches like Honeywell TL series are the only thing I will use for critical items/avionics.

 

[climberrn]

I use the automotive style blade fuses for non critical things and items that I don't intend to reset in flight. Heated seats, lighting, USB's, Lemo plugs....
Klixon for anything important. How are you going to power cycle a remote transponder or any other box without a power switch if it has a slow blow fuse?

 

[akschu]

I’m more in the hybrid approach. Stuff that I may be tempted to reset in flight get klixon breakers ( ignition and alternators ) everything else gets blade fuses and avionics with dual inputs get dual blade fuses on separate busses.

This way the decision on if it’s important enough to fiddle with in flight is already made, and critical stuff has more than one bus/fuse/wire.

 

[togaflyer]

I have a 24 circuit Bussman which uses ATC type blades. It is compact and takes significantly less room than standard breaker fuses installed on the panel. . I use all glow fuses, which if it fails the fuse will light up. Both alternator fields are push/pull breakers. Some like the ability to immediately reset the breaker in flight. There is usually a reason why the breaker tripped and my preference is to find out why on the ground and not in the air. I pull each fuse and inspect during my condition inspection.

Eaton's Bussmann Series 15713-24-12-22A Rear Terminal ATC Fuse Block,12/24VDC, 200A​

 

[JDA_BTR]

On that Eaton Bussman ATC block, do you know the part numbers for the pins you crimped for small wires? The data sheet shows a minimum wire size of 16 AWG. What did you do for 20-22 AWG wires?

 

[rv6ator]

I am using AFS Advanced Control Module (ACM) utilizing electronic circuit breakers. This is my first foray into the ECB world, so far so good.

 

[DanH]

Let's be honest here. The primary reason folks choose breakers is preference, not engineering. After all, real airplanes have breakers, and acres of breakers impress the passengers.

Why not talk about physical properties which may make a breaker a better choice in a specific situation? For example, I have one on a Plane Power alternator field supply, so transient OV events don't cause a crowbar interrupt. Why? A Bussman ATC fuse has an open time of 0.15 to 5 seconds at 200%. A Klixon 7277 at 200% of rated current is 2 to 35 seconds. A 7274 is 2 to 20 seconds.

 

[Mikeyb]

Let's be honest here. The primary reason folks choose breakers is preference, not engineering. After all, real airplanes have breakers, and acres of breakers impress the passengers.

Why not talk about physical properties which may make a breaker a better choice in a specific situation? For example, I have one on a Plane Power alternator field supply, so transient OV events don't cause a crowbar interrupt. Why? A Bussman ATC fuse has an open time of 0.15 to 5 seconds at 200%. A Klixon 7277 at 200% of rated current is 2 to 35 seconds. A 7274 is 2 to 20 seconds.

Roger That!
The best reference on EAB electrical system protection is still the AeroElectric Connection that is available everywhere. The fused marine load centers like Blue Sea Systems solve so many problems providing robust, safe screw terminals connections for both power and ground. Even if you need to parallel two of them. The ECB’s are probably the best choice for builders insisting on resettable/switching protection.

 

[jjb]

On that Eaton Bussman ATC block, do you know the part numbers for the pins you crimped for small wires? The data sheet shows a minimum wire size of 16 AWG. What did you do for 20-22 AWG wires?

(Delphi) Aptiv 12020334 Pack-Con Female Loose Terminal, III Series, 20-18 Ga. Do a search, many online vendors, brass or silver plated available.

 

[togaflyer]

My fuse box has the female blade. Stein Air build up the panel for me.

 

[bbaggerman]

My thoughts:
I toss tons of Tyco breaker/switches in the scrap bin, worthless POS.
Fuses, ok for lights and misc stuff but not for the really 'important' items.
Klixon breakers and high-quality switches like Honeywell TL series are the only thing I will use for critical items/avionics.

For the occasional in-line fuse the automotive style blade fuse is attractive but I never cared for the cheap PVC insulation that you get when you buy at the aviation aisle of O'Reilly Auto Parts. I found that LittelFuse has a couple of options for wire crimp in-line fuse holders, the MAXI 152 Series and the 150 Mini Series of in-line fuse holders. If you need just 2 or 3 of them LittelFuse is real generous about sending samples... hint hint. I use a couple of these in-line with the voltage taps from my current shunt.

 

[PilotjohnS]

One thing I would do differently, is put more things on the same breaker. For example, I would put the ahdrs and the magnetometer on the same breaker. If i pop the breaker, I would use the seperate G5. Also put the pfd and mfd on the same breaker. Since the pfd is fed by a second power input, so pulling the mfd breaker would not cause the pfd to go out. Many similar things like that can be put together. ( The pfd breaker has no value since it only controls one of the two power inputs)

 

[FinnFlyer]

I use the automotive style blade fuses for non critical things and items that I don't intend to reset in flight. Heated seats, lighting, USB's, Lemo plugs....
Klixon for anything important. How are you going to power cycle a remote transponder or any other box without a power switch if it has a slow blow fuse?

Pull the fuse and put it back in. Been there, done that.

 

[tass]

I have breakers everywhere except where impractical. The field sense wire to the regulator, and in-line with the second battery (which isn't used for starting). I didn't build the plane, though, but it is handy (though less compact than a fuse-box would be).

Interesting thing I only just found out was that with the fuse removed (or blown) on battery 2, the EFIS continues to report the battery as having >12v.
I thought I had some fundamental wiring screw-up, but the lighted fuse holder puts out about 12v on the wire when its LED is lit which is subsequently detected by the EFIS' battery2 sense wire.

To me this is very bad since I won't know I don't actually have an available second battery if this fuse had a reason to blow just before or during a flight. I bought some dumb fuse holders and will replace it.