The short circuit protection is triggered by a small hardware current sensing circuit, which will act as soon a certain current value is exceeded for a given amount of time (drive dependent and not user configurable - this protection will always disable the drive).
Normally this would only happen in case of a real short circuit on the drive motor outputs, but the current can increase to these levels in some other situations which don't imply a short circuit. It's possible that for a motor with a very low resistance and inductance and with an improper tuning on the current controller - the current can reach the threshold value in between 2 current loop samples (that is before the drive can try to regulate the current) and in this case the protection will be triggered.
While this is possible, is less likely to happen than the following scenario : the user will set the drive current limit to the near maximum measurable current on that drive (16.5A on an IDM680 for example) but because of the offset and measurement errors on the current, the drive will never be able to "see" the 16.5A, and while it will increase the voltage command "knowing" that it still needs to do so (because the imposed current is not yet reached), will result in quickly giving all the voltage available in an attempt to reach the 16.5A value (of course this will only happen if this much current is actually needed - you can very well have this setting but you won't see this happening until you really load the motor).
Now assuming that the motor resistance is small enough (which usually it is) then it becomes clear that the current will increase above the threshold level. In some cases the short-circuit protection can be followed by an under-voltage error which means that the power supply was overloaded and it automatically shutdown.
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