Difference between OFF1 ,OFF2, OFF3

I did not know the answer to that as well, but I checked it out, and see what I found

on this link: http://www.automation.siemens.com/WW/forum/guests/PostShow.aspx?PageIndex=1&PostID=215029&Language=en

Here is some brief but you can find it in the Manual also.

OFF1: OFF-1 means Normal Stop. Motor will stop in time defined as in Parameter i.e. Ramp Down time

OFF2: OFF-2 means Coast to Stop. Means drive will inhibit pulses and Motor will stop by it self with its own Inertia

OFF3: OFF-3 also means Normal Stop but it will stop in time defined in Parameter for OFF3. Like P466 in Master Drive.

Basically OFF-1 and OFF-3 will do same function but OFF-3 is generally defined for Emergency Stop. Drive will stop on OFF-3 on some fault to protect from high damage

As it is, it might not even just relate to AC drives only but even Siemens drives, I'm yet to confirm that though.

I add one score to Mr.Toba.

The OFF-3 is NOT normal stop. It is called "QUICK STOP". On activation of this input, the VFD brings the motor to a quick stop. This feature is permitted only in case of an EMERGENCY as this will stress the mechanical equipment. The shaft of the drive will be subjected to a large shear stress.

Hence this feature is activated in case of an emergency to avert damage to human / process conditions.