PDMX 126 with AM822 drivers and relays.

[m_c]

You need to split the power into two distinct groups. One being control power, the other being motion power.

Control power you generally want to remain permanently on, and powers things like the controller, input sensors, buttons, etc. Basically anything that being still active isn't going to cause motion.

Motion power is anything that powers things that move i.e. stepper drives, spindles, solenoids. Motion power you want to kill as quickly as practical in the event of an E-stop.

If you don't want to go to the expense of using a higher voltage for controls, use a 5V version of the relay I linked to previously, and do what Jazz said to create a latch. That way you can use the contact that's providing the latch, to also control the E-stop input on the BOB.

[Neale]

...and to get the fault signal to trip the latching relay, you can wire the fault outputs from the drivers in series with the estop switches, and any fault output or estop operation will trip the relay. I have three driver fault outputs and three estop switches all wired in series and it works a treat. It's that easy. The set of "switches" are wired into the supply to the relay and you just have to watch the polarities of the fault outputs when you wire them in.