Emergency Alternator Field Switch


Well-Known Member
I am reviewing the systems on the 310 in preparation to do some instructing in it and I was trying to come up with a good explanation on why the emergency alternator field switch is installed, what it does, and scenarios where the switch would be used.

The POH says, "The emergency alternator field switch is used when the alternators will not self excite. Placing the switch in the ON position, provides excitation from the battery even though the battery is considered to have failed." The only time the emergency procedures call for the use of the switch is when a dual alternator failure occurs and the field fuses are still good and the circuit breakers have not tripped.

My understanding, is if the alternator field is disrupted and the alternator ceases to provide current, the emergency field switch is used to provide a battery charge to the alternators to try and restart the field. Am I correct with that statement?

Also, what are some reasons that the alternator field may be disrupted?