jeffmeh said:Yes, it shunts hot to ground to trip the GFCI breaker. There are some religious arguments around whether that is a good approach, but it will work, assuming the GFCI is good. Another approach is to wire the e-stop to the coil of a normally open SPDT contactor, through which both hot lines pass upon entry into the control panel.
I don't think the e-stop is necessary, but I do highly recommend having the "main power contactor" that I described above, triggered by a switch. When the switch is off, the only hot wires in the panel are at the switch and at the line terminals of the contactor. When you plug in or unplug the control panel, all of the other components are powered down. You may not be able to switch it off as quickly as an e-stop, but close enough, and you could use the e-stop for the switch if you so desired.
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