ESC Wiring

I'm putting together my first electric model and purchased the Flite Test Power Pack F. I don't understand how the 20A ESC is configured. It has the 3-phase motor outputs on one side, and on the other it has the XT30 connector for input power, a 3-wire BEC that goes to the receiver/FC, and an additional 2-wire connector with medium gauge red and black wires. I assume those carry some kind of current, but what is it for? I have Googled every ESC diagram I could find but none of them have that extra connector. Thx