Z-14 circuit protection and diode-isolated power feeds

[Raiz]

Many of the avionics boxes now come with dual diode-isolated power feeds and I'm wondering what is best practice for circuit protection when using a Z-14 (dual bus) architecture.

With a separate feed to every box from both buses, you end up with a lot of fuses or breakers . It might also be confusing, because pulling the breaker or fuse for one feed still leaves the box powered via the other feed. On the other hand, powering each box from one bus only gives up the redundancy that the avionics designer intended.

Has anyone been down this route before? Any thoughts on best practice?

 

[Mich48041]

I recommend Z-13/8, which is Bob Nuckolls favorite. Keep it simple and light weight.
I am not necessarily recommending the suggestion below, but offer it only to meet your goals.
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If local regulations allow it, use two sets of fuse blocks that are NOT mounted on the instrument panel. The fuses will not be accessible in flight. But they do not need to be because if one fuse blows, its partner on the other fuse block will supply power to the device. If the second fuse also blows, there is a big problem with the device that no amount of new fuses will fix. As far as pulling fuses, that should only be done while safely on the ground with lots of time to find the correct fuses.
If a fuse should happen to blow, how will you know it? The glow type fuses require a load to be connected in order to glow. If the load is supplied by the other fuse, then the blown fuse might not glow. The fuses will need to be tested periodically.

 

[newtech]

I am wiring up a new RV-7A build with a complete Garmin touch panel. Garmin recently started using diode OR power inputs so some of the equipment has dual inputs and some doesn't. This build has dual isolated power buss', i.e. dual batteries, master solenoids, fuse blocks, etc. I have been holding off writing about our approach until the plane is a little farther along but now is as good a time as any to put it up for peer review.

Just a quick picture of the panel being built up on the work bench. Will post pictures and description of our approach tonight.