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Individual Circuit Breakers vs Electronic Circuit Breaker System

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In my RV-8 if I am going to go one step beyond a simple change to the panel I remove the whole center panel. Mine is similar to Walt's photo above (by no coincidence) so I remove the GDU, avionics and backplates and then drop the circuit breakers out the back as a unit. Removing all the nuts on the breakers common to the same bus bar. Then the whole center panel comes out. Then I can really get to things, including the back side of the wings. It might add about half an hour to 45 minutes to the job but it makes it super easy to change wiring, CAN Bus etc. It's just a bunch of screws, some breaker nuts and a couple of dimmer knobs with allen head set screws. Having the center panel out also makes it easier when I am adding a breaker or changing devices it is also easier to drill the hole and center and apply the new label on the bench. For some reason mine always turn out crooked when I try to do it in the airplane. I use the standard 3/4" lateral spacing for Klixons and buy the pre-drilled bus copper bars (AN P/N) that use 3/4" centers for the holes. Those bus bars help keep the breakers together when pushing them out of the panel as an assembly.
 
In my RV-8 if I am going to go one step beyond a simple change to the panel I remove the whole center panel. Mine is similar to Walt's photo above (by no coincidence) so I remove the GDU, avionics and backplates and then drop the circuit breakers out the back as a unit. Removing all the nuts on the breakers common to the same bus bar. Then the whole center panel comes out. Then I can really get to things, including the back side of the wings. It might add about half an hour to 45 minutes to the job but it makes it super easy to change wiring, CAN Bus etc. It's just a bunch of screws, some breaker nuts and a couple of dimmer knobs with allen head set screws. Having the center panel out also makes it easier when I am adding a breaker or changing devices it is also easier to drill the hole and center and apply the new label on the bench. For some reason mine always turn out crooked when I try to do it in the airplane. I use the standard 3/4" lateral spacing for Klixons and buy the pre-drilled bus copper bars (AN P/N) that use 3/4" centers for the holes. Those bus bars help keep the breakers together when pushing them out of the panel as an assembly.

Do you have a source for those " pre-drilled bus copper bars (AN P/N) that use 3/4" centers for the holes"?

Thanks!
 
Do you have a source for those " pre-drilled bus copper bars (AN P/N) that use 3/4" centers for the holes"?

Thanks!

Mil Spec part number:

MS25226-4-N where N is the number of holes (ACS has them in 8 hole position size). Or perhaps -10's might work better on Klixons than dash 4's. Both will probably suffice.

Here are some NOS online at a fraction of the price:

https://www.ebay.com/itm/254817103584
 
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Exp Bus quit

I had a similar experience to N816kc. My RV-6 had an ExpBus that worked fine for several years and one day quit. I couldn't figure out why or what in it broke so took it out and replaced it with something I could understand (toggle switches and breakers).
 
Circuit breakers are mechanical devices with moving parts. CBs can fail open or closed. One time I tested a CB on the work bench before installing. I applied over current and instead of opening the circuit, the breaker actually smoked. I decided not use a circuit breaker in my plane. Here are sources for fuse blocks:
https://www.connectorconcepts.com/bu15reteatcf4.html
https://www.waytekwire.com/item/46075/EATON-s-Bussmann-Series-15713-24-12-22A-ATC-Fuse/
https://www.waytekwire.com/item/46074/EATON-s-Bussmann-Series-15712-14-06-21A-ATC-Fuse/
AirCraft Spruce Rear Terminal Mini Fuse Panel part #: 11-13348 - - $57.95
 
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Great questions. The shorted phone cord would cause failure when re-inserted into the USB power port. It was like flicking an on and off switch. VPX was fairly responsive on the front end but didn't seem to pursue things once it was determined to be a bad charge cord. My hangar mate is one of my best friends and owns the RV-8 and was the customer of record and he enlisted me to help. So to be fair let me review the final disposition with him. I am the sparky and he is a brilliant fellow who built his 8 but he doesn't own a laptop or do systems. So I would have been in the middle of any further troubleshooting were there any. The VPX Pro was installed by a very reputable shop that is one of the best during a G3X panel update about 18 months prior. And it worked perfect before and after the charge cord event.

Upon reviewing the VPX failure event with my hangar mate, his interaction with VPX on the issue was exactly as I remembered. They didn't seem to excited about the problem and called it solved after the phone charge cord ended up being the culprit. Seems to me they would have wanted to dig in and find out how a 3rd party charge cord plugged into the panel-mounted USB port could take down the whole VPX system, which can be critical for flight safety.
 
Circuit breakers are mechanical devices with moving parts. CBs can fail open or closed. One time I tested a CB on the work bench before installing. I applied over current and instead of opening the circuit, the breaker actually smoked. I decided not use a circuit breaker in my plane. Here are sources for fuse blocks:

Lets see, CB's have millions if not billions of flt hrs in airlines and GA aircraft, how many VPX's out there?
 
We get it

We get it; YOU don’t like the VPX…

That does not make it bad or unsafe.

Everyone has their own level of risk aversion…
 
Originally Posted by Mich48041 View Post
Circuit breakers are mechanical devices with moving parts. CBs can fail open or closed. One time I tested a CB on the work bench before installing. I applied over current and instead of opening the circuit, the breaker actually smoked. I decided not use a circuit breaker in my plane.

Lets see, CB's have millions if not billions of flt hrs in airlines and GA aircraft, how many VPX's out there?

We get it; YOU don’t like the VPX…

That does not make it bad or unsafe.

Everyone has their own level of risk aversion…

Don't think I said any of those things...
 
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FWIW, my RV-8 has one pullable circuit breaker, for the alternator field. Buss fuse blocks for all else. They swing down from under the panel for easy access, which so far has been only when I want to add something.

...
Same here, but mine are not (easily) accessible in flight. If a fuse blows, I'll land to troubleshoot.

Honeywell mechanical switches - they seem very well-made.
 
the biggest con I have is someday, not maybe, but someday, one of the parts in that box will become EOL, and that will be the part that fails. (I'm in the process of redesigning one of my products because one of the few single supplier parts just went EOL.) then you have two solutions, find a serviceable unit, or re-wire the airplane. I just don't see enough positives except you get a really cool display of your electrical system on a screen to take that risk.
bob burns
RV-4 N82RB
 
Why not both - ish?

the biggest con I have is someday, not maybe, but someday, one of the parts in that box will become EOL, and that will be the part that fails. (I'm in the process of redesigning one of my products because one of the few single supplier parts just went EOL.) then you have two solutions, find a serviceable unit, or re-wire the airplane. I just don't see enough positives except you get a really cool display of your electrical system on a screen to take that risk.
bob burns
RV-4 N82RB

I am in the throws of a RV-14 build, I enjoy the simplicity of fuses, but I also like the information the VPX type systems offer. I promised myself to build bone stock with no mods to keep the build moving along, I learned that lesson with our RV-10. But I am considering building an Arduino type device that would simply read the amps of each individual circuit and report via a web app to a phone or tablet. I think by using hall sensors we could read the amps without even breaking into the wires. Has anyone ever considered or done anything like this?

Jason Kreidler
RV-14 - Fuselage
 
But I am considering building an Arduino type device that would simply read the amps of each individual circuit and report via a web app to a phone or tablet.

I already have a device for that. It's called a Fluke multimeter. But here's the thing. In 1000 hours, I've never needed to know the amp draw of any circuit. A web enabled version seems like a new kind of cat video.
 
I don’t disagree

I already have a device for that. It's called a Fluke multimeter. But here's the thing. In 1000 hours, I've never needed to know the amp draw of any circuit. A web enabled version seems like a new kind of cat video.

Dan, I don’t disagree with you. Just one time, when we had a circuit breaker tripping on a landing light randomly it might have been useful to watch that circuit. Turned out to be a bad breaker. So in 800 hours there was that one time…. Ok, back to my promise of bone stock. - Jason
 
I already have a device for that. It's called a Fluke multimeter. But here's the thing. In 1000 hours, I've never needed to know the amp draw of any circuit. A web enabled version seems like a new kind of cat video.

Exactly. Once current draw is measured to determine design objectives it need not be measured again. I do this on the ground with a metered and regulated DC power supply. If something goes south it will find you by popping the associated breaker. The odds are very slim something will go “just a little bit south” and be reflected by a slight increase in current - even if the pilot is constantly monitoring it.

For that matter, I do not install current shunts. Voltage tells me the health of the system.

Carl
 
For that matter, I do not install current shunts. Voltage tells me the health of the system.

Carl

I like knowing total alternator/system current load, it gives you battery state of charge and total system load, good info that costs nothing to monitor.
 
Uh oh, it's mighty dark inside the mouth of this alligator! :)
<snip>
5) If you can find flexible bus cables rather than solid bus bars, use 'em. They make replacement of a failed breaker much easier. HINT: Some business jets and regional airliners which are being retired are good places to source these bus cables.

Canada - I've never heard of flexible bus bars, that sounds like a great idea. Is this a large diameter wire with "holes" in it? Can you share more info?

Lets see, CB's have millions if not billions of flt hrs in airlines and GA aircraft, how many VPX's out there?

Originally Posted by Mich48041
Circuit breakers are mechanical devices with moving parts. CBs can fail open or closed. One time I tested a CB on the work bench before installing. I applied over current and instead of opening the circuit, the breaker actually smoked. I decided not use a circuit breaker in my plane. Here are sources for fuse blocks

Walt, Joe (Mich48041) is saying he put fuses instead of circuit breakers, not putting a VPX instead of circuit breakers.
 
I like knowing total alternator/system current load, it gives you battery state of charge and total system load, good info that costs nothing to monitor.

Like Walt, knowing I had the input capacity on my engine monitor, I installed a Hall Effect current sensor in both the alternator B lead and the battery feed wire. This way I can see both how much juice is being produced by the alternator and how much is being consumed from the battery (especially helpful in a situation where the alternator has failed - guesstimating how much power is left in the battery can be aided by knowing battery output current and voltage).
 
This is what is on Airbus uses. If you want to buy new, AirCostControl supplies most Airbus part numbers.
 

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I roll my own "bus bars"..., not as elegant as Airbus but works just the same.
I prefer this over 'open/exposed' copper bars, doesn't need to be massive as most brks are under 5A.
Another reason I like breakers is the ability to 're-boot' the box (computer) in flight by a simple breaker reset.
 

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Walt's "roll your own" type of wire bus interconnect seem to have more service loop if it is needing to change things around, compared to the Airbus short run flex cable. I honestly typically don't have a problem dropping out a whole row of breakers attached to a rigid bus bar for maintenance. One just needs to get mentally by the idea of removing 5 or 8 nuts and star washers and then pushing the whole row of breakers out of the panel instead of trying to deal with just the one that needs maintenance. The other breakers along the bar stay put and in good alignment due to the rigid bus bar.
 
I roll my own "bus bars"..., not as elegant as Airbus but works just the same.
I prefer this over 'open/exposed' copper bars, doesn't need to be massive as most brks are under 5A.
Another reason I like breakers is the ability to 're-boot' the box (computer) in flight by a simple breaker reset.

For those using this idea, be careful of accumulating load. If you daisy-chain 4 5A breakers in a row, and supply the bus power at one end, that wire needs to be able to carry 20A. Should be 12AWG. 6 5A breakers in a row would need a 30A capable wire! You start to see why many use the copper bar.
 
Walt, Joe (Mich48041) is saying he put fuses instead of circuit breakers, not putting a VPX instead of circuit breakers.
I wondered why he quoted my post. I never realized he thought that I was recommending a VP-X. I don't. I recommend fuses. How often do you replace fuses in your ground vehicle?
 
For those using this idea, be careful of accumulating load. If you daisy-chain 4 5A breakers in a row, and supply the bus power at one end, that wire needs to be able to carry 20A. Should be 12AWG. 6 5A breakers in a row would need a 30A capable wire! You start to see why many use the copper bar.

I'm not that good with math so please correct me if I'm wrong.

Req'd wire size is all about volt drop/temps, so lets say the entire 'bus' has 6" of 20ga wire, at 9 ohms/1000' that would be approx 5 mohms (.005 ohms.)

So that would give a VDrop of 150mv (.15V) worse case scenario (30 amp load) on the far end breaker.

It would also be less than the above as the breakers on the source end would be less, only the breaker on the far end would have the max voltage drop and only if the other breakers were carrying their max load (which they do not).

Most of the glass panel stuff that calls for 5A breakers actually use less than half of that in normal operation.
(just checked current draw of the GDU460 is listed at 2A but specs a 5A breaker which is typical)
 
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I wondered why he quoted my post. I never realized he thought that I was recommending a VP-X. I don't. I recommend fuses. How often do you replace fuses in your ground vehicle?

My bad, the thread started as CB vs VPX is all.
 
I'm not that good with math so please correct me if I'm wrong.

Req'd wire size is all about volt drop/temps, so lets say the entire 'bus' has 6" of 20ga wire, at 9 ohms/1000' that would be approx 5 mohms (.005 ohms.)

So that would give a VDrop of 150mv (.15V) worse case scenario (30 amp load) on the far end breaker.

It would also be less than the above as the breakers on the source end would be less, only the breaker on the far end would have the max voltage drop and only if the other breakers were carrying their max load (which they do not).

Most of the glass panel stuff that calls for 5A breakers actually use less than half of that in normal operation.

Your math would make sense if that bus wire was the only drop in the system. You have longer wire supply leads to the devices. You would like the total drop to any device to be less than 5% (some people say 3%). So by your calc, you have already incurred 1/4 of the total allowable voltage drop, just getting to the breaker (under admittedly worst-case situation).

I really like to have the bus provide full voltage (essentially zero drop), so that the voltage drop calcs on the wire leads from there to the device is the whole drop. Some devices are more sensitive to supply voltage than others. Becker radios in particular will complain if the supply voltage drops below 11.5V, and I get complaints from my Becker AR4201 frequently in my glider.
 
Req'd wire size is all about volt drop/temps, so lets say the entire 'bus' has 6" of 20ga wire, at 9 ohms/1000' that would be approx 5 mohms (.005 ohms.)

So that would give a VDrop of 150mv (.15V) worse case scenario (30 amp load) on the far end breaker.
.

For short runs (e.g., like this) the limiting factor is the temperature. For your example, the first inch will be generating about 1 watt of heat. That may not sound like much, but, have you ever put your finger on a resistor generating one watt of heat? It will be quite warm. And its designed to transfer heat to the air. Your wire insulation will tend to keep that heat inside.
 
For short runs (e.g., like this) the limiting factor is the temperature. For your example, the first inch will be generating about 1 watt of heat. That may not sound like much, but, have you ever put your finger on a resistor generating one watt of heat? It will be quite warm. And its designed to transfer heat to the air. Your wire insulation will tend to keep that heat inside.

Very true, but if all the breakers were actually carrying 5A they would all pop. The Garmin GDU460 10" display for example specs a 5A brkr but actually lists the load at 2A, so basically all those numbers are less than half worst case values calculated above.
 
I really like to have the bus provide full voltage (essentially zero drop), so that the voltage drop calcs on the wire leads from there to the device is the whole drop. Some devices are more sensitive to supply voltage than others. Becker radios in particular will complain if the supply voltage drops below 11.5V, and I get complaints from my Becker AR4201 frequently in my glider.

If you're running the std 14.5v on the bat bus getting 13.5v to the avionics stack should be easy peasy despite a few drops. Most devices will start to go out around 11-11.5V so nothing unusual there. If you want 0 VD then you'll be carrying around a bunch of extra weight to get there is all.
 
If you're running the std 14.5v on the bat bus getting 13.5v to the avionics stack should be easy peasy despite a few drops. Most devices will start to go out around 11-11.5V so nothing unusual there. If you want 0 VD then you'll be carrying around a bunch of extra weight to get there is all.

That’s nice when you have an alternator on board. Too bad they don’t make 14v batteries. In gliders some folks cobble together a 2V with a 12V. Can’t do that with LiPo4
 
I roll my own "bus bars"..., not as elegant as Airbus but works just the same.
I prefer this over 'open/exposed' copper bars, doesn't need to be massive as most brks are under 5A.
Another reason I like breakers is the ability to 're-boot' the box (computer) in flight by a simple breaker reset.

Thinking more about Walt's proposed "bus" as depicted here. Under the doctrine that the breakers (fuses) protect the wiring, what breaker protects those bus wires? The 60A main breaker on the alternator feed? How hot would a 20AWG wire get passing 30A in Walt's example voltage drop? What does AC43.13 say about appropriate wire gauge for 30A? I'm just suggesting paying attention to the worst-case loads and sizing wires appropriately. In the case Walt posted, perhaps there is a 20A Avionics bus breaker upstream of that chain of smaller breakers?

Really - I'm not trying to pick an argument with Walt here. But there are reasons why it is customary to use a hefty conductor as a main bus off of the 60A main breaker. Whether it is a flex bus as used apparently by Airbus, or a copper bar (which can be covered with shrink tubing where it is exposed between breakers), it needs to be able to carry a lot of current without getting hot or causing any voltage drop.

I don't think there's 3 lbs of wire in my whole airplane if I discount the 2AWG cable from the battery to the starter, which in my case is 2 lbs (I weighted it) because my battery is in the back. How much can you really save by scrimping on wire gauge?
 
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Very true, but if all the breakers were actually carrying 5A they would all pop. The Garmin GDU460 10" display for example specs a 5A brkr but actually lists the load at 2A, so basically all those numbers are less than half worst case values calculated above.

Walt, I disagree with this design philosophy. The point of the CB is to protect the wire in case of a malfunction; in case the device pulls 4.5 amps instead of 2 the wire must handle it since the breaker won’t trip. A wire feeding 6 five amp breakers must handle 30 amps safely.
 
Thinking more about Walt's proposed "bus" as depicted here. Under the doctrine that the breakers (fuses) protect the wiring, what breaker protects those bus wires? The 60A main breaker on the alternator feed? How hot would a 20AWG wire get passing 30A in Walt's example voltage drop? What does AC43.13 say about appropriate wire gauge for 30A? I'm just suggesting paying attention to the worst-case loads and sizing wires appropriately. In the case Walt posted, perhaps there is a 20A Avionics bus breaker upstream of that chain of smaller breakers?

Really - I'm not trying to pick an argument with Walt here. But there are reasons why it is customary to use a hefty conductor as a main bus off of the 60A main breaker. Whether it is a flex bus as used apparently by Airbus, or a copper bar (which can be covered with shrink tubing where it is exposed between breakers), it needs to be able to carry a lot of current without getting hot or causing any voltage drop.

I don't think there's 3 lbs of wire in my whole airplane if I discount the 2AWG cable from the battery to the starter, which in my case is 2 lbs (I weighted it) because my battery is in the back. How much can you really save by scrimping on wire gauge?

Walt, I disagree with this design philosophy. The point of the CB is to protect the wire in case of a malfunction; in case the device pulls 4.5 amps instead of 2 the wire must handle it since the breaker won’t trip. A wire feeding 6 five amp breakers must handle 30 amps safely.

Bob: The math in my previous post shows that the bus method I use can easily handle the worst case load.

Steve: maybe you should review some of the Z diagrams, the 60A bkr I assume you are referring to is the alt feed, it has nothing to do with the bus feed which is protected by the main contactor only, main bus feeds are generally not fused.
 
...in case the device pulls 4.5 amps instead of 2 the wire must handle it since the (edit: 5 amp) breaker won’t trip. A wire feeding 6 five amp breakers must handle 30 amps safely.

I understand your point, so this is just a practical check. The probability of all six 2-amp devices drawing 4.5 at the same time is pretty low. In fact, the probability of all six devices even being turned on at the same time is low.
 
I understand your point, so this is just a practical check. The probability of all six 2-amp devices drawing 4.5 at the same time is pretty low. In fact, the probability of all six devices even being turned on at the same time is low.

To further this practical check just a little, my full Garmin panel (3 screen/GTN750/dual comm/xpdr/AP etc) with everything on pulls about 8 amps with the GTN being about 1/3 of that.
 
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To further this practical check just a little, my full Garmin panel (3 screen/GTN750/dual comm/xpdr/AP etc) with everything on pulls about 8 amps with the GTN being about 1/3 of that.
I feel like I’m beating a dead horse here. If we could always count on things behaving there would be no need for CB’s at all. A decent circuit breaker/wire size design should keep you from burning up even when the attached devices all conspire to kill you.
I’ll also say again, that for short runs it’s the heat load you need to be concerned with.
 
....
I’ll also say again, that for short runs it’s the heat load you need to be concerned with.

Which is why I asked about Walt's example. 6" of 20AWG wire with 30A. From his resistance and voltage drop calc, that's 4.5 watts. I don't have a sense of how hot that piece of wire is going to get. Seems like a piece of 20AWG wire with 30A running thru it would have a new name. "Fuse".
 
Which is why I asked about Walt's example. 6" of 20AWG wire with 30A. From his resistance and voltage drop calc, that's 4.5 watts. I don't have a sense of how hot that piece of wire is going to get. Seems like a piece of 20AWG wire with 30A running thru it would have a new name. "Fuse".

35C rise for AWG20 @ 7 amps. AeroElectric Chart. and 200C @ 17 amps per Mil HDBK 508

I am guessing pretty hot if on for very long.
 
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35C rise for AWG20 @ 7 amps. AeroElectric Chart. and 200C @ 17 amps per Mil HDBK 508

I am guessing pretty hot if on for very long.

Of course that assumes a long wire in ambient air. In this particular example, a lot of the heat will flow thru the copper - to the circuit breaker! I don’t know what happens from there.
 
Good discussion but let’s get back to reality, If I use the rating of all the breakers I installed in the panel according to you guys I will need a a wire the size of the battery cable running to the avionics bus... mind you for a panel that draws 8 amps. Hmmm, reality vs meltdown theory, which one to believe, (starting to sound like a debate on vaccines with my kids which I can’t win either, so I'm out!).
 
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I wired my RV6 just like Walt’s picture in post number 71 of this thread. Not one single circuit breaker pop in 25 years.

I’ve been flying around thinking I was safe, when in reality, according to some of you, I’m just a nanosecond away from my first circuit breaker pop and turning into a flaming fireball.
 
Going back to OP's question:
The amount of confusion demonstrated by this thread around the relatively simple question of ground wire thickness might argue for going with an ECB blackbox as a safer choice for many. Despite it being a single point of failure one would think it was competently designed by professionals who knows how to compute the total amps through a simple parallel circuit.
-c
 
Hear the valiant knights of the Holy Grail… “Run away!”

I’m having flashbacks of the new technology called the Global Positioning System and how we should only let our ADF’s be pried from our cold, dead hands…

This whole “fear the solid state device” thing is humorous for me.

If you’re building an airplane on a budget, use fuses. But for everyone else building a $200K+ airplane, enjoy life a little… use a VP-X. I have heated seats too. ;)

If you’re poo-poohing the VP-X because it’s somehow a “black box” (which isn’t really accurate) and not to be trusted, as in “if you want to use that device, go somewhere else”, you should really study the available data on solid state versus mechanical device reliability. Full disclosure, I built two aircraft using circuit breakers and bus bars, which worked fine. But I’ve also had zero issues with my “black box” VP-X systems that I’ve installed, both the Sport and Pro.

While concerned about the reliability of the solid state technology in the VP-X, compare your Garmin or Dynon ADAHRS to your old vacuum pump and consider which is more reliable and which you’d prefer in IFR conditions. And then consider a backup anyway. And that’s what I did with my VP-X installations.

I’m on my second VP-X build, this one being a Pro and built-out fully, much like Bob’s -10, with every circuit used - actually every pin in the device is in use. But then I also have a separate emergency bus for my critical loads, such as my EFII (oh, wait, we might need to rehash EFII vs carburetors again as well). And I also have a G5 with a separate backup battery. And an auxiliary battery. And a backup alternator.

There is risk to everything in life; the key is determining your level of acceptable risk, and then managing to that.

There’s a lot of variability with our experimental aircraft, with a big variable being how we perform component installation. Pointing to a single failure, or even multiple ones, shouldn’t preclude someone else from venturing into using the technology. Using the logic that a failure occurred with a particular component, therefore we should not use that component, leads to the logic that if an RV-10 crashes because the Lycoming engine stopped, we stop using Lycoming engines. Or maybe we just shouldn’t install the engine with RTV in the fuel system.

There’s lot’s of details to be learned about so many things… a curious detail is the dearth of information on supposedly unreliable VP-X systems. Food for thought: I still have the stinging memory of the cost that came with replacing all of my circuit breakers on my Baron after an AD came out years ago declaring the models I had no longer airworthy.

Closing thought: A black box is defined by Oxford’s encyclopedia as: “any complex piece of equipment, typically a unit in an electronic system, with contents that are mysterious to the user”. Having pulled the cover off of the VP-X and having become familiar with the internal components, I find that it’s a fairly simple design and well laid out - significantly the dual bus system. Maybe becoming more familiar with the technology will make it less daunting for folks.
 
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Good discussion but let’s get back to reality, If I use the rating of all the breakers I installed in the panel according to you guys I will need a a wire the size of the battery cable running to the avionics bus... mind you for a panel that draws 8 amps. Hmmm, reality vs theory, which to believe (starting to sound like a debate on vaccines with my kids so I'm out!).

Honestly all we are talking about here is using a 10AWG wire for the first daisy chain bridge and the feed to it, and 12AWG for the rest. No one said anything about a battery cable.
 
Consider the needs of the load

One very important consideration when runnning power to modern electronics is to remember that most units have switched mode power supplies powered from primary power producing all the secondary equipment voltages. Switched mode power supplies are generally sensitive to primary power input impedence- the control loop stability margins are directly related to supply power impedence. Putting a large capacitor (22,000 microfarads) on the distribution bus can improve the situation. Having a highly loaded piece of 20awg goes in the other direction. If a number of pieces of equipment are supplied through one 20awg wire the total current average load may be within acceptable limits from a voltage drop or heat load but the instantaneous current draw when all switched mode converters just happen to align may be a couple of orders of magnitude greater resulting in drop outs and converter instability. Such intermittent issues are really hard to troubleshoot and resolve.
KT
 
Going back to OP's question:
The amount of confusion demonstrated by this thread around the relatively simple question of ground wire thickness might argue for going with an ECB blackbox as a safer choice for many. Despite it being a single point of failure one would think it was competently designed by professionals who knows how to compute the total amps through a simple parallel circuit.
-c

Agreed. One would think. But what if a single USB power port connected to one alleged isolated circuit feed takes down the whole ECB system and the competent design professionals exhibit indifference to finding out what caused it?

You can have the best hardware in the world that when combined with buggy software or unforeseen mechanical or circuit issues in the field that can cause surprises. Just ask Boeing about the ingenious suction lavatory introduced on airlines in the 1960s. It was a real wonder of science and technology. A rare proud moment for payloads designers everywhere. Who said the glory days of aviation was dead? And then on one of the first revenue flights the fat lady sat on one and flushed it sucking here down tight against the seat where she stayed for the duration of the flight until ground crew could help her by releasing the vacuum. So Boeing try as hard as it might during the design had only thought it had covered all possible worse case scenarios. I guess not. They added a pressure relief to the design and everything was hunky dory until the same thing happened again on a 767 flight from Scandinavia to the USA 20 years ago. Are we getting fatter or did some new hire at Boeing miss the lessons learned section left over from the 60's? Maybe both. But it sure didn't help the fat lady.

So competent initial design is tempered and optimized through lessons learned in the field. Refining and improving design requires tackling any problems that raise their head after release and I didn't get the feeling that the VPX guys were very interested at all in investigating a total system failure. Even after the fat lady had a red oval impression in her thighs. Just sayin'
 
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