Hi BRpilot,
unfortunately I am not referencing any data here just memory. Unlike a lot of medium twin helicopters, the AW139 bus tie is OPEN/OFF when in NORMAL position. I believe the QRH says to select bus tie ON in the event that the affected engine with chip may shut down thus losing the generator. Saying that I think the bus tie switch does automatically close if you lose and engine/gen anyway...is just to be on safe side.
I could be wrong and happy to be corrected
Regards, SS