Aileron trim installation power source?

I'm installing an electric aileron trim servo, should it be powered from a servo master switch, or can it be powered directly from a +12v source?

I used a switch to deal with the dreaded runaway trim problem. I doubt I will be able to react to a real runaway in time to make any difference, but I ran out of things to put on my switches. You could even double it up with your autopilot servos power switch.

What I did

I have electric aileron, elevator and flaps, each one controlled through the MAC stick grip switches, but their power source is individual breakers. I wanted capability to disable each one individually.

Aileron and Elevator trim on one pull breaker. Flaps on another. Autopilot servos on another pull breaker.

I use the auto trim feature on the SkyView autopilot to provide trim switching functions for the stick top hat switch. It also provides a three second lockout of trim motion (a mitigation for run away trim). This works both when autopilot is on and off.

Carl

In talking with a couple of other RV owner/builders in the area, neither of them have any "quick" remediation for runaway trim servos. It's clear that it's standard practice to be able to quickly disconnect all autopilot servos, but not necessarily the trim servos. I understand that there's a flight test to control the plane with a stuck trim, it's not something that's easy, but it can be flown.

I have an Aerotronics panel that was ordered by the previous builder, and it does not include a trim servo master switch, and also has an EXP Bus that uses solid state current limiters, meaning no physical CB to pull, even it you did catch and realize that a trim servo was "running away".

Is it actually more common to wire the trim servos, without a master switch?

TCW makes this for exactly what you’re trying to do. YMMV Bob.

https://www.tcwtech.com/product/safety-trim-intelligent-servo-controller/?v=7516fd43adaa

Wonderful looking device.... But, one more failure point in the system, lots of wires to install, expensive, another manufacturer to rely on.

If a runaway failure of a trim servo can be mitigated with brute force, and that's been the Van's philosophy with the design, why would I add another component into the system?