Electronic circuit breaker

[hais]

I heard it mentioned a few times that electronic circuit breakers are not allowed for certified aircraft. However, reading the circular below, the section on remotely controllable CBs implies that electronic ones are allowed.

Is it just a matter of certifying electronic CBs (not implying it is easy), or is there a fundamental regulatory barrier? 

I'm dreaming of CBs you can reset on your MFD...

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25_1357-1A.pdf&ved=2ahUKEwi-35Gi5qD2AhVFqlsKHWCWDMYQFnoECFEQAQ&usg=AOvVaw0wYv9xkl03Lgp4X8VvCvXl

[N201MKTurbo]

I worked for an industrial automation company for the last 11 years. A few years ago we switched exclusively to electronic circuit breakers. I’ve never seen one fail.  They are easy to use, take up less space and are more accurate. 
 

That being said, they have some failure modes that might not be the best choice for aviation. 
 

They are run by a microcontroller, a single point failure for many circuits. 
 

They dominantly fail open, this is safer, but could turn everything off. 
 

The current mechanical circuit breakers are amazingly reliable with nearly a century of reliability data. It is a hard sell to replace that with a little convenience. 
 

 

[jaylw314]

I did some reading up on the Vertical Power type electrical systems in the RV community, and it seemed a pretty good idea.  Like @N201MKTurbo said, I heard of some issues with software, where one switch would affect the switch state of another, and it only got fixed with a software update.  Those are the sort of things you don't want to hear. 

I thought I recalled VP strongly recommended installing hardware switches even if it could be controlled by electronic device as a backup

Conversely, a major advantage is that all the switches become low-current data connections, so you don't have as much of a fire hazard behind the panel, and you use a lot less heavier gauge wiring (some weight savings).

The main problem is that none of the devices (that I know of) are PMA'd for GA, and I doubt you'd find an IA or FSDO willing to sign off on it as a modification

[N201MKTurbo]

20 minutes ago, jaylw314 said:

I did some reading up on the Vertical Power type electrical systems in the RV community, and it seemed a pretty good idea.  Like @N201MKTurbo said, I heard of some issues with software, where one switch would affect the switch state of another, and it only got fixed with a software update.  Those are the sort of things you don't want to hear. 

I thought I recalled VP strongly recommended installing hardware switches even if it could be controlled by electronic device as a backup

Conversely, a major advantage is that all the switches become low-current data connections, so you don't have as much of a fire hazard behind the panel, and you use a lot less heavier gauge wiring (some weight savings).

The main problem is that none of the devices (that I know of) are PMA'd for GA, and I doubt you'd find an IA or FSDO willing to sign off on it as a modification

An electronic circuit breaker will never reduce the wiring. The same High current wires will need to be run, they just need to run through the electronic circuit breaker instead of the mechanical breaker. 
 

Some of the current electronic circuit breaker systems do some of the bussing internally, but it still has the same wiring in the end.

[hais]

22 minutes ago, N201MKTurbo said:

An electronic circuit breaker will never reduce the wiring. The same High current wires will need to be run, they just need to run through the electronic circuit breaker instead of the mechanical breaker. 
 

Some of the current electronic circuit breaker systems do some of the bussing internally, but it still has the same wiring in the end.

What if the CB were distributed? Say, you have a cable assembly that supplies power and contains a data bus, and the device end of the cable has a CB with own built-in SW that can report status/send heart beat down the data bus.

Would that come with significant weight and installation savings?

[N201MKTurbo]

37 minutes ago, hais said:

What if the CB were distributed? Say, you have a cable assembly that supplies power and contains a data bus, and the device end of the cable has a CB with own built-in SW that can report status/send heart beat down the data bus.

Would that come with significant weight and installation savings?

The idea is to have circuit protection for each device. The circuit breakers are there to protect the wiring, not the devices. You cannot put the breakers at the device end of the cable, that doesn’t protect the wiring.

With what you propose, if there was a short circuit in the circuit breaker, your plane would catch on fire and kill you.

[jaylw314]

1 hour ago, N201MKTurbo said:

An electronic circuit breaker will never reduce the wiring. The same High current wires will need to be run, they just need to run through the electronic circuit breaker instead of the mechanical breaker. 
 

Some of the current electronic circuit breaker systems do some of the bussing internally, but it still has the same wiring in the end.

Only in the sense that you don't need any of the high current stuff behind the instrument panel anymore--the power wires go from main bus to breaker, and then breaker to device without having to make the extra loop to the instrument panel switches (and the electronic breakers can actually be next to the battery, with a data cable to all the switches in the panel).  For that matter, you can forgo things like the flap and gear motor relays.

So yes, all your devices still need the same power, but the runs can be done more efficiently to use typical gauge wiring more efficiently, at least in theory.  In practice, things may be very different, of course, and I've yet to see anyone use it in an RV build.

Edited February 28, 2022 by jaylw314

[hais]

2 hours ago, N201MKTurbo said:

The idea is to have circuit protection for each device. The circuit breakers are there to protect the wiring, not the devices. You cannot put the breakers at the device end of the cable, that doesn’t protect the wiring.

With what you propose, if there was a short circuit in the circuit breaker, your plane would catch on fire and kill you.

So you would want to place the breaker as close as possible to the power source. What is the logic for airliners? Is the power bus  running the length of the airplane without protection.

[carusoam]

4 minutes ago, hais said:

So you would want to place the breaker as close as possible to the power source. What is the logic for airliners? Is the power bus  running the length of the airplane without protection.

Expect that a large power supplying wire has circuit breakers or fuses near either end… 

Small CBs protecting devices…

Large CBs protecting busses…

Large fuses protecting supply lines…

 

A method of stopping the flow of electricity if insulation gets worn through, or gets a screw poked in it…

PP thoughts only  not a mechanic…

Best regards,

-a-

[hais]

3 minutes ago, carusoam said:

Expect that a large power supplying wire has circuit breakers or fuses near either end… 

PP thoughts only  not a mechanic…

Best regards,

-a-

Makes sense. I misunderstood the purpose of the requirement to have the CBs accessible by the pilot, I thought the main purpose was to protect against failure in the device, and to provide a way to reset the device.

[carusoam]

Newer long bodies have a row of CBs in the tail….

Older LBs have fuses back there…

They are things that a pilot isn’t going to want to reset a CB for… without inspecting first…

My O1 is all fuses… in the tail…

Best regards,

-a-

[N201MKTurbo]

1 hour ago, hais said:

So you would want to place the breaker as close as possible to the power source. What is the logic for airliners? Is the power bus  running the length of the airplane without protection.

I haven’t studied airliners in a while. I believe they have generator breakers at the generators. They are remotely actuated from the cockpit. The main power buss runs through the floor to a bunch of places. The main avionics and other system breakers are on the bulkhead behind the pilot.