The green wire is the factory installed bonding jumper between the neutral and the frame. The other end of it is connected to the center screw on the terminal strip but you can't see it from the picture because its connected on the back side. If a 4-wire cord is used then this green wire needs to be disconnected from the frame screw and taped up or many instructions tell you to connect it to the center terminal with the neutral wire which connects it to itself.
Curt
