Username Protected wrote:
A separate field switch with connection between the main bus and regulator power replaced it.
The concern is if the battery master is turned off with the alternator operating the main bus will continue to be powered by the operating alternator with already excited field.
I don't understand the concern. Are you thinking about a scenario where the pilot turns the master off in response to an electrical fire or burning smell and the alternator keeps the bus powered? It is true that if the battery master doesn't remove power to the regulator(s) with a separate pole or mechanically linked alternator switch, the bus would remain powered with the master off until the engine stopped or the alternator was overloaded. I think the solution to that would be to simply turn the alternator off along with the battery if you want to depower the bus.
My airplane (B55) doesn't have a mechanical interconnect between the battery master and the alternator switches but it's battery master does remove power to the regulators (via the alternator switches) when off.
I was working on a Cessna 340 today and noticed that there's a bail that the pilot can use to simultaneously move the battery master and both alternator switches off but it's also possible to turn the battery off and leave the alternators on. I suspect that in that case the alternators would power the bus with the battery out of the circuit.