Why does my PowerFlex 525 Fault every time the Safe Torque Off is activated?

This article describes how to disable the PowerFlex 525 STO Fault without compromising Safety

A fault F059 (Safety Open) on a PowerFlex 525 drive can indicate that both of the safety inputs (Safety 1, Safety 2) are not enabled. 

If you do not want the drive to fault on a F059 (Safety Open) when removing the  Safe Torque Off (STO) inputs then you can change Parameter T105 [Safety Open En] to be a 1 [Fault Disable]. The STO circuit will still function in this configuration but will no longer announce a fault.