Some one help me make sense of what I'm seeing.

I bought an old desktop CNC machine and at some point some one replaced the control electronics with their DIY version which uses a parallel port breakout board and microstep controllers. I'm in the process of rehousing the electronics and what I'm seeing with the wiring doesn't make any sense to me.

They've got two opto relay blocks wired in series with the main power, one of them to switch on the spindle motor and one of them...appears to do nothing except be a terminal block for wires since I'm pretty sure it's always on.

They've taken a wire from the emergency stop button which is parallel to the main power and put it on the control side of the opto relay and then put the output of the emergency stop to the load side of the opto relay. So from what I can tell the e-stop button bears the full weight of cutting power to the machine while the opto relay does nothing.

They've also put something that looks like a PTC thermistor or a MOV across the control terminals of the opto relay, between the main power and the common neutral, any idea why they would do this?