How many of us have an avionics master system that if it fails will take out way too much?

How about the panel master switch? In my Certified Bonanza there is such a switch that can take down all the electrons. With vacuum gyros this is probably OK.

In my IV-P I had such a contactor, it is an all electric airplane. Having been burned once I now have two contactors that operate in parallel. The two panel split rocker switches that control the two alternators control the master contactors independently.

How does the Avionics master switch work in your plane? What happens if something simple happens like the control wire breaks.

All excellent questions.  My approach (not the best, but the best I could think of at the time):

1)     I have dual busses and dual alternators that feed an essential buss via diodes.

2)     I have an avionics switch.  But it is double pole, so I can select power from the A buss or the B buss.  Diode feed from either A or B is probably simpler and automatic.   I also have a cross feed relay.

3)     In case the A buss relay or B bus relay fail, my sequence is load shedding, and then to feed power to the failed bus via a by pass switch running through a 30 amp fuse.  Thus I can also fly with both A and B buss relays out (to save power) and operate at reduced load with the manual switch bypass.  I labelled this switch “Emergency Power.”  Call me paranoid, but relays (and that means big relays including contactors) do fail.

So I have two ways to feed to each buss, and two ways to supply power to the avionics buss and the essential buss.

Paranoid Fred