Radio master/breaker

[gbarrier]

Was talking with a friend today about radio masters. We both agreed that neither of us were very happy with all of our avionics running through one switch. Several of the light twins we had operated used a relay which actually made contact when the power to the relay was off (switch mounted upside down) while others had a switch and a second switch labeled emer. avionics. Think I'll install a second switch. As I look the install over I am reminded that my radio master is actually a 30 amp breaker switch and I have to ask "why did they do that". Are they all like that or has someone along the way installed the breaker switch. Sure would like to know why Maule chose to limit total avionics use to 30 amps. How is your's wired?

[riverbuggy]

A 30A breaker is what you would use for a household clothes dryer. You must have some pretty powerful transmitters in your avionics stack.
Just make sure that any wire downstream of the breaker is at least #10 gage. Doesn't sound like an original equipment installation to me.

[gbarrier]

Don't see the need for the breaker at all since all it does is tie the avionics buss to the main buss. Most installations just have a toggle switch or relay. All avionics have their own breakers on the avionics buss.

[riverbuggy]

In that case it is not being used as a protection device at all. It's only function is just a switch to control power to the avionics buss. However it would still protect the main buss upstream of the switch if a major short should happen on the avionics buss itself.

[gbarrier]

Yep, that's the case. Been doing some reading. Understand if the Avionics buss is more than a couple of inches from the main buss a breaker switch is in order in case the wiring between them short. Now, in our Maules they are right next to each other but guess it does provide some protection to keep the main buss onboard if there is a short on the Avionics buss.

Think I'll move all the avionics breakers one hole to the right and add a second breaker switch. I'll paint the bat handle red and label it Aux avionics master. Guess if I want to retain the 30A protection I should also placard something to the effect of only one master on at a time.

[ajak]

Some larger aircraft I have flown use split (dual) avionics masters to avoid a single point of failure. I know of at least one incident in a company I used to fly for where that would have come in handy. Many turboprops with more complex electrical systems also use current limiters to protect entire busses. They're kind of like "last chance" slow burn fuses. They'll only burn out if there's something major wrong on the bus, like a shorted power lead that's not on an individual circuit breaker. If they do ever burn out, it requires maintenance action to replace.

I've been thinking about doing something similar, i.e. a current limiter right at the battery, to protect everything else downstream.