looking for power distribution opinions

With all the Garmin stuff I'm installing, panel space went down, while power distribution needs went up. With that in mind, I'm planning fuse blocks on a swing down tray between the panel and sub-panel, as I've seen others do. Mission critical stuff and anything that might be prone to voltage nuisance trips like motors and whatnot will be on a breaker.

*before we get down in the weeds, i understand that the reason for circuit protection is for the wiring, and I understand how to size a wire/breaker for the load.

*probably not interested in going with the vertical power magic box in place of fuses/breakers- yeah, I get that it's easy and makes for a tidy installation, but I don't like the idea of being AOG because of the failure of one critical box that I can't work on, plus most of the additional features can be handled by the gad27

here's what I'm thinking;

Breakers-

Alt field
P mag 1
P mag 2
Boost pump
Pitot heat
Flaps
Autopilot controller & servos (gmc507 & gsa28 x2)
electric trim x2 (ray allen)
Fuse block /buss 1
Fuse block/buss 2


Fuse block- 1

PFD (gdu460)
transponder (gtr 45r)
AHRS/Magnetometer (gsu25 & gmu11)
engine monitor module (gea 24)
system controller (gad27)
Audio panel (gma245)
IFR GPS (gtn650)
comm 1 (gtn650)
spare
spare

Fuse block -2

Backup horizon (g5)
MFD (gdu460)
Comm 2 (gtr20)
backup battery power input (IBBS)
nav/taxi (flyLED)
strobe/land (flyLED)
cabin lights/panel lights
usb charger
spare
spare

One primary question you may have picked up on based on what I listed above;

What is the consensus of powering each of the fuse blocks from a breaker? I normally wouldn't be crazy about the idea of fuses downstream of a breaker, but it seems like it might make sense here. I'm a big fan of the ability to load shed. It would also be nice to power up stuff individually during software uploads. Putting big breakers upstream of each fuse block accomplishes both of those.

does this pass the sanity check?

PM Sent...

About those circuit breakers. If they are not installed, they can not fail.
Usually it is a bad idea to put circuit protection devices in series.
A hard fault could not only blow a fuse, but also trip the circuit breaker.
It is unlikely, but possible because it takes time for a fuse to blow.
You don't want a whole bus to go down.
Current much larger than the fuse rating will flow for a fraction of a second.
Have you ever noticed that some household circuit breakers have 10,000 amps
printed on them in fine print? How can a 15 amp breaker allow that much current to flow?
Because it takes time for the breaker to trip and the power company transformer is capable of putting out lots of current.
I know a guy who worked on an electric range outlet without shutting the power off.
He accidently shorted out the hot terminals with a screw driver. Not only did the circuit breaker for
the range outlet trip off, but so did the main breaker for the apartment building.

Joe, thanks for the input. That is a failure mode I hadn't considered and it bears thinking through.

does this pass the sanity check?

Click to expand...

A lot of this is preferences vs sanity. Here’s my 2 cents (I have a mix of switchable breakers that are accessible in flight and fuses that are not):

I have breakers for each major “screen” - reasoning:
- I’ve never met a computer/screen that didn’t occasionally lock up requiring a power-off reboot. Garmin has occasionally proven this to be true (though there is a 3-button push that reboots in most cases)
- for software updates, selective powering keeps the battery drain lower
- load shedding in an alternator failure can be mission specific as to what you can shed.

Note also, the GTN boxes have 2 functions - radio and GPS - that are powered separately and can be switched/breakered separately (mine are for the above reasons)

Switches for devices allow load shedding when using fuses - switchable breakers do the same (e.g. I have COM 1 switched/fused off an E-Bus, COM 2 is on a switchable breaker off the Avionics bus - personal preference)