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benbell4140

Well Known Member
I'm starting to wire up everything and have a question about the avionics buss. I plan on using a breaker switch for the avionics master, this will protect the buss. Do I need to fuse or breaker each component after the buss?? Like transponder, nav, com etc.. I'm new to this whole wiring thing and want to get it right the first time.

Thanks
 
Hi Ben, breakers aren't there to protect the component, although that is a nice side-effect. Breakers are put in to protect the wiring. So while your big switch-breaker will blow if something starts eating 40 or 60 amps or more, if one single component fed by a single tiny wire starts drawing that kind of current the wire could overheat and possibly ignite.

So any item on the bus should have its own fuse or breaker. Auto fuses are a good cheap way to protect things, with the downside that you can't easily re-set them in flight (although that's a whole other debate in itself). The fuse or breaker should be sized to the wire, and it's acceptable to use a lower value fuse or breaker if you want but never a larger one than the wire was designed for.

AC 43.13 is a good reference, although wordy.
 
My understanding is that if you use a single fuse/breaker for all your avionics connected to the avionic bus, in the event of a malfunction of one item, you'll loose all the avionics at once. I think is better to protect each single item with it's own fuse/breaker. This way, in the event of a malfunction of one item, all other avionics will continue to work properly.
 
I'm working on converting all my hand drawn electrical notes to CAD, so I happen to have my electrical drawing on my desk. I used the architectures from AeroElectric Connection to develop my architecture.

I have 4 main fuse blocks and a few breakers.

I have an "Always Hot" fuse block with a few items (clocks) that are always on.

I have my Main Bus on a 12 position fuse block with Starter, Alternator Field, fuel pump, lights, etc.

The same lug that is the Input to the Main Bus is used has the Output to my Essential Bus (via a Shotky Power Diode).

The E-Bus consists of 2 fuse blocks. The first fuse block just powers my Engine Monitor and the control relay to my backup alternator.

The second fuse block in the E-Buss (another 12 position block) is wired through my Avionics Master Switch. So the 2nd fuse block on the E-Buss is really my Avionics Bus.

Each of my avionics components has it's own fuse. In fact, my GNS480 Nav/Comm uses 2 power inputs, so it has 2 fuses - one for the Comm side and the other for the Nav side.

I run Breakers off the Main Bus for Flaps and Trim - in case I should want to pull a breaker for one of these systems
 
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