Klixon circuit breakers as switches

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dtnelson

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My two cents; first, use a CB or fuse sized to protect the device, not the wire. Many times I've heard that the CB should be sized to protect the wire under maximum load, while the device (or load) on that wire is drawing only a fraction of the current that the wire can manage. That makes no sense to me... if you protect the device, you've by definition protected the wire...

Second, use the right DC rated switch and a separate CB or fuse wherever you can. I've used circuit breaker switches in several of my panels, and I've had them fail. In one case I even had one fail resistively; in other words, not open, not closed, but it was internally dropping enough voltage to cause the com radio it controlled fail. In my current airplane, I do have some CB switches (Tyco W31 series, like this) - and I've learned that I need to have a spare or two in my onboard tool kit.

Third, use "pullable" circuit breakers like this, instead of like this. You may find yourself in a situation where you need to isolate just one device on a circuit branch instead of all of them (think of your "radio master" branch). If you have a case where you know, with some certainty, which device is failing and causing the main breaker to pop, you might consider pushing that breaker if you can isolate and remove the defective device. That's pretty much the only time I'd consider resetting a breaker in flight.

Fourth, I'm personally not a big fan of "hidden" fuses, if only because I want to know which fuse has blown so as to know what else won't work in flight.

My two cents,

Dave
 

BJC

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My two cents; first, use a CB or fuse sized to protect the device, not the wire. Many times I've heard that the CB should be sized to protect the wire under maximum load, while the device (or load) on that wire is drawing only a fraction of the current that the wire can manage. That makes no sense to me... if you protect the device, you've by definition protected the wire...
Size the wire to provide the current needed to operate the device (the load).

Size the over-current protection (fuse, breaker, or solid state device) to protect the wire.

There is no way to protect the load / device with the overcurrent protection because the device must have an internal failure to lead to an over-current condition.


BJC
 

BJC

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Second, use the right DC rated switch and a separate CB or fuse wherever you can.
There are many switches that are rated for AC that perform acceptably for nominal 12 and 24 volt systems. There also are some DC rated switches that are of a quality that I would not put in an airplane.


BJC
 

bmcj

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Why do breakers have to occupy valuable real estate? They can be mounted anywhere within reach, even out of sight. Resetting is only a matter of tactile sense... run your fingers across the row and feel for the raised breaker, then reset. That way, your switches can go where they need to be.

One other note... breakers and fuses are meant to protect against excessive (fire inducing or instrument destroying) power flow. If you trip a breaker, it’s not always a good idea to reset it inflight. Given that, why would you want to circumvent their primary purpose just to use them as switches?
 

BJC

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Marc Zeitlin

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Aircraft Spruce has them too:


for about $30 - $50 each, depending - not $200. I used to have one of these in my panel to turn on the Nuckolls design "Emergency Bus". Always worked fine, and with a life of 6K - 10K cycles, would have more than lasted the lifetime of the plane.
 

Daleandee

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Well, two chances to set the plane on fire is 100% more than one chance. No thanks. In my airplane's electrical system design (per Bob Nuckoll's Z-14 diagram) ALL fuses are inaccessible in flight, and NO fuse is safety critical, meaning that any one fuse can blow and the plane does not have an emergency situation.
I used Bob's diagram for my own build. Fuses and switches for me. In an earlier scenario it was suggested that if the radio were to trip the breaker around a busy airport then resetting the breaker to restore comms would be an option. My answer would be to squawk 7600 and look for the light gun (if a towered field) as I prefer to do my airplane maintenance/repairs on the ground.

Dale
 

wktaylor

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An electrical fire is a terrifying and deadly prospect in-flight. Following best/professional-practices usually results in a robust/safe/worry-free/low-maintenance system.

Switch in-line with a circuit-breaker is Your best/safest/standardized-bet... except for CB functions incorporated into a 'flip-switch'... which I am unsure exist in aviation.

Conventional push-pull [pole-type] circuit breakers [CBs] are intended for current over-load protection, only. In military aviation they are NEVER to be used as a flight 'switch'.

NOTE.
CBs should be tested regularly by pulling/resetting to 'wipe-the-contacts' of any micro debris/welding/oxidation/corrosion... and ensure the snap-lock, springs, case etc are still functioning properly. An experienced mechanic will know instantly if there is an unusual 'feel difference'... then removal/replacement or removal/current-overload testing is mandatory to validate it for return-to-service. During certain types of maintenance... for safety purposes... mechanics 'pull-out the CB' ['off' state] and put a plastic collar/tie-wrap around the shank to prevent it from being inadvertently 're-set' [to an 'on' state]… which is then removed and the CB is re-set after maintenance.

Useful FAA ACs/documents on this subject...

AC25.1353-1 ELECTRICAL EQUIPMENT AND INSTALLATIONS
AC25.1357-1 CIRCUIT PROTECTIVE DEVICES
DOT/FAA/CT-TN94/55 ELECTRICAL SHORT CIRCUIT AND CURRENT OVERLOAD ON AIRCRAFT WIRING
FAA ANM-01-04 WIRING POLICY BRIEFING
https://www.mitrecaasd.org/atsrac/nbaa/1415-WiringRegulationsandPolicies.pdf
https://www.mitrecaasd.org/atsrac/meeting_minutes/FAA_Policy_Statement_ANM-01-04.pdf
FAA AIRCRAFT EWIS PRACTICES JOB AID 2.0 AIRCRAFT ELECTRICAL WIRING INTERCONNECT SYSTEM (EWIS) BEST PRACTICES - JOB AID
FAA AIRCRAFT WIRING PRACTICES - AN INTERACTIVE TRAINING AND SELF-STUDY COURSE (25827)
FAA BRD-127 THE ROLE OF EXTERIOR LIGHTS IN MID-AIR COLLISION PREVENTION
FAA FSAW 2-10 ELECTRICAL WIRING INTERCONNECTION SYSTEM (EWIS) PROTECTIONS AND CAUTIONS DURING MAINTENANCE AND ALTERATION

WarStory.
My high-end mini van from 2007 has experienced many small/frustrating electrical problems with recurring maintenance and a few very serious charging/ignition system failures. What a pain.
My 2019 state of the art car [luxury] has electronics galore... software being the biggest factor for maintenance. HOWEVER... as SAE specs-documents... and on-line discussions reveal... due to the massive demands for reliability of the base-vehicle electrical/electronics systems... old/low-grade wiring-interconnection/routing/components are/is no-longer acceptable due to the sensitive/high-speed EE-EL components, such as sensors, computers, cameras, etc... This 'crap' is not up-to-the task for latest generation cars. For this/other reasons, highly integrated vehicles have adopted [aircraft?] quality EE-EL components, wires, workmanship, etc just to ensure safe/consistent/long-term operation without frustrating 'spark-chasing' that is costly/counterproductive/unsafe. When I opened the hood and looked all around/under this vehicle the quality of EE-EL parts/workmanship is evident... and NECESSARY.
 

BJC

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CBs should be tested regularly by pulling/resetting to 'wipe-the-contacts' of any micro debris/welding/oxidation/corrosion... and ensure the snap-lock, springs, case etc are still functioning properly.
That is a good reminder.

Thanks,


BJC

PS: When I had been on the job at a new power generation plant as a full-time employee for a few months (I previously had worked there as a co-op student), I got a call from the corporate office that “Jack is coming to visit.” Jack was a VP, who’s absolute passion was protective systems. When he arrived, all he said was, “Show me the book.”

The book was the documentation of all the protective relaying systems for the four generator station plus the associated substation and the remotely-operated hydroelectric generation station. It required dated and signed entries of all required periodic testing, calibration, and corrective maintenance. Accomplishing everything within the specified schedules was challenging, because much of the work needed to be done during forced or scheduled outages, which were the highest work load periods.

As I handed the book to Jack, his hand was trembling. He sat down, started looking through it, and gradually began to relax. When he finished, he handed me the book, said “Good job” and walked out. After that, I got no warning that he was coming, but he showed up at least twice a year to repeat the procedure.

There are protective schemes that open breakers to prevent or limit damage to equipment, but those schemes are monitoring much more than just time and current.
 

TFF

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When I was at a regional airline, we had a crew hold in a CB in, because they did not want to lose some instrument that they could have worked around. They had to scrap about 20 CBs and a bunch of wire on the panel, because of the melted wires that the original wire burned through because it stayed energized. Rule is one reset. If it holds ok. If not, tough; move on.
 

opcod

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Canada
The way i see this, is Klixton are quite perfect and sure it cost a bit more , but they are a 2 in one unit.. not only a switch. And if i recall: you have to change tire and do maintenance every x hr. Perhaps if a 20$ is too high, the whole price cost for an airplane is quite high and trying to save 1-3$ is the wrong way of thinking and lead to failure and accident.
 

Wanttaja

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For what it's worth, I use automotive blade-type fuses and individual holders. These are labeled on one side, with a dot of velcro on the other. I wire them to hang behind the instrument panel near the bottom below the device they're connected to, with a matching bit of velcro to to hold them in place. There's enough wire to let them come down an inch or so to let me examine/replace them.
fuse.jpg
I don't carry spare fuses in the airplane. I figure if a fuse blows, I'll wait until I'm on the ground to trouble-shoot. Since I'm running a conventional magneto ignition, there's nothing that can't wait until I'm back home. Just have a radio (panel-mounted handheld), a transponder, and ADS-B. There's an avionics master switch and a switch for the ADS-B power.

I've also got a single Klixon-type breaker for the generator output.

Ron Wanttaja
 

Pops

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For what it's worth, I use automotive blade-type fuses and individual holders. These are labeled on one side, with a dot of velcro on the other. I wire them to hang behind the instrument panel near the bottom below the device they're connected to, with a matching bit of velcro to to hold them in place. There's enough wire to let them come down an inch or so to let me examine/replace them.
View attachment 94801
I don't carry spare fuses in the airplane. I figure if a fuse blows, I'll wait until I'm on the ground to trouble-shoot. Since I'm running a conventional magneto ignition, there's nothing that can't wait until I'm back home. Just have a radio (panel-mounted handheld), a transponder, and ADS-B. There's an avionics master switch and a switch for the ADS-B power.

I've also got a single Klixon-type breaker for the generator output.

Ron Wanttaja

Oh, the joys of a simple airplane.
 

Mad MAC

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There are many switches that are rated for AC that perform acceptably for nominal 12 and 24 volt systems. There also are some DC rated switches that are of a quality that I would not put in an airplane.
It should be pointed out that technically there is not way to derate an AC switch for DC rate, without either testing it or a detail design analysis, due to the fundamental differences in the design requirements between AC & DC switching.

Fuses & CB's do perform slightly differently in the time and current required to trip / blow.

One should always consider out breaks stupidity, I have heard of bored pilots closing collared breakers to see what would happen while in flight (this was on freighter conversions, always lots of capped and stowed wires with a sea of permanent collared breakers).
 

BJC

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It should be pointed out that technically there is not way to derate an AC switch for DC rate, without either testing it or a detail design analysis,
Yup. My comment was not intended to suggest such a scheme.


BJC
 

User27

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Try Potter & Brumfield W28 breaker switches or
ETA 1110 Series
The ETA breaker are simple push on/push off and shows a white collar when "popped".
These are European links, but Mouser US must have something similar
P&B W28
ETA 1110 Series
 

dtnelson

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Size the wire to provide the current needed to operate the device (the load).

Size the over-current protection (fuse, breaker, or solid state device) to protect the wire.

There is no way to protect the load / device with the overcurrent protection because the device must have an internal failure to lead to an over-current condition.


BJC
Hi BJC,

My point is this; many people (including me) will use 20 gauge wire for many runs. The American Wire Gauge table, which we should all be using, tells us that 20 gauge wire can carry a consistent 11 amps. While considering that bundled wires, long runs, and wires under a constant load can require a larger gauge, very (very) few wires in, at least, my airplanes will be carrying 11 amps consistently.

Let's do some math to check this. Using 20 gauge wire as an example, and considering a 5 foot run, the wire will have a resistance of 0.05 ohms end to end, a voltage drop of 0.56 volts (at 11 amps), and the heat generated will be 1.23 watts/foot. This is pretty much worst case, as few of us would be running a constant 11 amps down a 20 gauge wire (at any length).

So, for many of my radios and other devices that require 2 amps or less, are you suggesting I use an 11 amp circuit breaker? Or a 10 amp breaker? I doubt it.

This was my point; in those cases, of which there are many, I'd select a 2 amp, or even a 5 amp CB before using a 10 amp CB. That would protect the device before protecting the wire. Using heavier gauge wire just means carrying around lots of extra weight. Using a larger CB than the device requires means I'm willing to cook my radio while the wire is fine.

Peace,
Dave
 

BJC

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That would protect the device before protecting the wire.
Help me understand: protect the device from what? You might minimize the amount of smoke that leaks out following a failure, but how can you prevent a failure in the device by using an external breaker?


BJC
 

dtnelson

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There are many switches that are rated for AC that perform acceptably for nominal 12 and 24 volt systems. There also are some DC rated switches that are of a quality that I would not put in an airplane.


BJC
Hi (again) BJC

Regarding switches, you are absolutely correct that quality matters whether the switch comes with an AC or DC rating.

The difference is this; Because AC current goes from 100% of the voltage, to 0%, and then back to 100% at whatever the frequency of the signal is, the duty cycle is, (going from memory), something like 70%, instead of the 100% that a DC signal presents. That's harder on a switch. Also, given that when you flip the switch on an AC signal the electrical transition point is likely not at the 100% voltage peak, AC is easier on the contactor(s) than DC is. That's why switches have a DC rating.

This is not to say that you can't, or shouldn't use AC rated switches. Just be aware of those differences.

Peace,
Dave
 
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