I have recently been troubleshooting a component on a CNC machine. The device is connected via etherCAT to the machines controller. There is also a power cable that goes to the component. Basically the component is one electronic board that controls some gas valves. I have been told that the electronic board can be “short circuited” if I removed the cables and insert them again while the power is on. Is this true-if so-why?
CMOS logic is notorious for SCR latchup if any voltage is applied to signals before power is applied including residual charge that has the capacity to exceed the forward current rating on the two stage 5~10mA ESD protection diode clamps to each rail.
Since long cables have more capacitance (100pF/m) than the human finger tip (100pF in the IEC model of HBM), they can damage CMOS with cable charges with static from dragging on a carpet for example or any other tribolectric generation.
You ought to know how SCR's are used as DC crowbars across the supply, you don't want your logic chips to do this. (e.g. STM, Microchip PIC or ARM chip)
This is an intrinsic SCR Latch-up effect in CMOS logic.