Just to add another wee bit, you may see the other safety relay at the side of the red one, it is powered from the start/stop button on my panel, below the E-Stop, see pic.
What that button does is start the contacters for Drives and coolant however the power for the red E-Stop module is via the relays on it and also the E-Stop to CSMIO/Mach is via the red one. So I can start the computer and have Mach running but I can not take Mach out of reset unless the drives contacters are powered.
Hood