Hey Atroz,
if you search for “Emergency Stop” in the forum, you will notice that there are two very different kinds of Emergency Stop or Poweroff. For the one which we discussed above, which is described here and which means to prevent the spindle to run in case you open the enclosure door or during a bit change (or simply quickly halt the program to prevent it doing something with the workpiece you did not intend), you don’t forcibly need some special switch, in fact you only need a pushbutton (see circuit) and also a reset button to release the emergency state afterwards. Note that such a circuit can be wired to integrate the “estop” mode of the Onefinity Controller. A smart Emergency Stop mode, with no power cut off, just everything halted safely.
The completely different “Emergency Power Off” means, in case of fire, you quickly want to separate the whole installation from electricity. This is usually a big red/yellow button near the door of the room. Since such a total power cutoff does not take into account the state of the machine (spindle may still have been running), it’s not the ideal way to switch the spindle off and it can do harm to your VFD in case the spindle still runs. But, of course, this is a type of Emergency where the state of your machine doesn’t matter that much anymore, you just want the firefighters to be sure that the installation is cut off from electricity so they can spill water on it to prevent the building burn down.