I've found a reference to e-stop in the HY VFD manual - it seems that it's possible to define one of the digital input pins to accept an e-stop signal. I need to go through the manual in more detail to find out which of the many parameters will control things like e-stop ramp-down time, or if it just chops output and uses DC braking. I also assume (I'm doing a lot of assuming at the moment) that it will need an external braking resistor to give best results. More research...

My current e-stop switches are built from modular components and are single pole at the moment but could easily have a second pole added, wired either as an independent mechanism or via the second channel of the safety relay. But again, I have to come back to the appropriate level of protection. But then, I'm the guy who removed the chuck guard from his vertical mill as the first action after installing. Instead, I bear in mind that it would be an error to insert finger into revolving cutter.

This thread has drifted some way from the original question about enable pins on drivers, but I don't think that there has been a definitive answer to that one yet...