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?
Electrical – How to electronics “short circuit” when you plug in cables
cablespower supplyshort-circuit
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I'd be willing to bet that the J1 connector provides access to a pair of remote sense leads. These would be extended to the actual load so that the power supply can account for the voltage loss in the power leads. With up to 63A getting pumped out the voltage at the load could have dropped a fair bit. You can read more about how it works here: http://power-topics.blogspot.com/2008/07/what-is-remote-sensing.html
Usually these kinds of arrangements have either a switch or a pair of jumper wires attached that tie the sense leads to the local output of the power supply but that doesn't seem to be present on that jumper block.
A motor is an inductor, which attempts to maintain a constant current. When the motor is switched off, the current that was flowing in the motor prior to turn-off must continue flowing. Since the previous power source (the battery) has been disconnected, the only way for current to continue to flow is for the motor to drive that current with a voltage of its own. The voltage across the inductor (motor) will be whatever voltage is required for the current to continue flowing, and if this current must flow through an open switch (a device designed to prevent current flow), the voltage will be very high.
This alone doesn't blow the fuse. Your typical automotive fuse works essentially by melting from excessive current. But, the motor can't make current higher than it was; it's just increasing voltage to maintain current.
However, there is also overvoltage protection in the car's electronics, most commonly in the form of a crowbar circuit:
Here, the LM431 and triac normally do not conduct. However, if the voltage becomes higher than a threshold determined by the designer, the LM431 triggers, in turn triggering the triac. The triac essentially shorts out the power supply, as if someone threw a crowbar across the rails (thus the name of the circuit). This brings the voltage down, and the excessive current blows the fuse, disconnecting the power source and isolating the fault.
The solution is to put a snubber across the motor, providing a path for the current associated with the magnetic field collapse that isn't through the protection circuitry. In this application, the snubber can be a simple flyback diode. I'm guessing that your car vacuum was manufactured in China and was very inexpensive. By the sounds of it, they could not justify the cost of a power cord of significant gauge, so I doubt they could justify a diode, or the engineer to tell them that it's necessary. Alternate solution: buy a less crappy vacuum.
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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.
https://en.wikipedia.org/wiki/Latch-up