Hi PosClimb,
The Source Off light is necessary to show when the last manually selected source is no longer powering the Transfer bus, but the Transfer bus is still powered.
For example if a generator was lost, providing the bus transfer switch is in Auto, the Bus Tie breakers will automatically close allowing the offside generator to power the affected side's Transfer bus. In this case as both Transfer busses are still powered, the Transfer Bus Off lights will not be lit.
Hope this is of some help.
Regards,
MHA.
Last edited by MaxHelixAngle; 17th October 2010 at 01:59.
Reason: Punctuation.