Connection of Gen. B and Master relay

I would pull the 30A breaker to cut power.  

Thanks Mike,  No issue with the Gen B circuit not having any load?

I imagine it could overheat the components but that would be the least of my concerns if there was a fire or other issue that warranted pulling ship power.  

From what I hear the upcoming RS regulator would fix that issue.  

All makes sense, thank you.

Pulling the breaker will work, but be aware that doing so will create what's known as a load dump.  This is a large inductive voltage spike that occurs when the load is suddenly removed from a charging system.  The spike can exceed 100V and take nearly half a second to decay.  This can affect the regulator and anything connected to the bus.

Of course, if the airplane is filling with smoke that's the least of your concerns, but it's not a technique you should practice just to see if it works.  It will, but possibly not without consequences.

Other than the 30A breaker, there's no way to shut down the airframe electrical system once the Gen B circuit is online.  The Lane B switch controls the B side of the ECU; it doesn't control Gen B (it's not even monitored by the EMS).

Also, there's no overvoltage protection in the Gen B system, so a failed-short SCR in the regulator could potentially apply full rectified stator voltage to the bus.  Rotax warns about this in the 912iS Installation Manual, §24-00-00, page 15 (attached below).  Hopefully the RS regulator that Mike mentioned will solve this problem as well.