I remember vfd can reverse the motor rotation by local pad. And When I used a-b vfd this is the only way to change motor rotation. But when I work on ETN vfd, I change motor rotation by switching two wires. Why?
Etn? You mean Eaton? If you have an Eaton VFD that has a set of reversing contactors down stream of it, it's only because someone had no idea what they were doing. ALL VFDs can reverse a 3 phase motor, the direction of rotation on the output side is 100% manufactured by the VFD, so making it go ABC or ACB is just a matter of internal programming that can be changed either on the keypad, a communication port, or assigned to a digital input function.
I'm guessing that there is something different at play here. Most likely you are looking at an Eaton Soft Starter, not a VFD. Soft starters cannot change the direction of rotation. They are also not a Variable Speed technology, they can only ramp the torque temporarily and must eventually get to full speed.
A less likely but possible scenario is that someone has inappropriately used a 3 phase Eaton VFD to try to vary the speed of a single phase capacitor start motor. If that's the case, changing the rotation of two of the phases would not change the motor direction, you must change the internal motor connections to the capacitor, which would require swapping wires with a contactor. But if this is what's going on, failure of the motor, VFD or both is right around the corner, neither device is designed for this. Even though it's possible to make it appear to work, it's only an illusion that takes place right up to the point at which the magic smoke escapes.
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