Adding a hot bus for ignition

[toast]

My plane has an electrically dependent engine, currently the ignition power comes from the main bus. This means that a failure in 1. the battery, 2. the master solenoid 3. the master switch and 4. the ignition switch could cause the engine to stop (not the most ideal).

What I plan to do is run a second wire from the main battery to a small hot bus which could then power the ignition and cabin lights. This cuts my number of switches that can fail the engine down to 1. My ignitions have 3amp fuses (only one is ever active at a time) and my cabin lights use an additional 2amps. I'm planning to use 18 gauge wire, which is a little bit bigger than what's strictly necessary, but if I ever did have another component I wanted on the hot bus (unlikely but you never know).

I'm curious if this seems reasonable, or if there is something else I'm missing.

[Marc Zeitlin]

1 hour ago, toast said:

What I plan to do is run a second wire from the main battery to a small hot bus which could then power the ignition and cabin lights....

I'm not sure why Cabin Lights are at the same level of importance as "engine running" - if you have a flashllight (or your phone) in the cockpit with you, the Cabin Lights are superfluous.

In any case, as I've done about 14.3 bazillion times before, I will recommend that anyone architecting an electrical system for an airplane get Bob Nuckolls' book "The AeroElectric Connection". It has many prefab architectures from which one can choose to fit one's needs, and a fully electrically dependent engine is represented in a few of them. There are a number of his architectures that have an "Always Hot" bus, with redundancy in the case of system component failures.

Get it. Follow Bob's recommendations.

[toast]

The Aeroelectric Conversion is what gave me the idea to put the cabin lights on the hot bus. Though, in the age of led flashlights built into cell phones, cabin lighting is probably less of a concern that it used to be.