OK, I think this whole thing is being over-thought.:-)
1) Good and accepted practice is if it is enclosed in metal, ground the metal to the negative terminal of the power supply. Look at a PC. If you have ever put PCs together yourself from components, you may have noticed some of the supplied standoffs for the motherboard were brass, not plastic. The brass standoffs were placed where motherboard mounting screws connected to the groundplane holes of the mother board.
2) Take an Ohmmeter. Touch one probe to the ground pins of the parallel port. Touch the other lead to any unpainted metal on the computer case. You will read a dead short. The computer case is grounded to GND from the PC power supply.
3) The same thing applies to our drives. Our drives have metal enclosures. Grounding the metal enclosure insures no matter what happens in the drive, the 'hot' side of the power supply will never appear on the case of the drive. The case is firmly connected to the GND terminal of the drive. This is both a shielding issue and a safety issue. You cannot have the case floating because you don't know what may touch it.
4) This has no effect on how you use the drives. They should be in a metal chassis. You should follow the same good practice and ground the chassis. Have a single wire run from the GND side of your supply to the chassis metal.
5) Never use the chassis as a GND distribution to the motor drives. Every drive GND input gets a separate wire going back to a single GND terminal on your power supply. Do the same for +VDC distribution to the drives. Every drive gets its own wire going from +VDC back to a single point on your power supply. This is called 'star distribution' because each drive gets two wires (+/-) emanating from the supply like sunrays.
6) Screw the drives down to your chassis. It makes no difference if the screw grinds through the drive's hard-anodized or not. The drive's case is grounded internally, your chassis grounded and you have a copper wire running from power supply GND to the drive power supply GND. Electricity prefers the path of least resistance and that is the copper wire.
7) That takes care of the DC side of proper grounding and power GND distribution. If you have the power supply inside the control box chassis and you are using a 3-prong AC receptacle, wire the receptacle GND to the same chassis point as you wired the power supply GND to. This carries your chassis ground to earth ground (that big pipe pounded 10' into the ground near your circuit breaker box) so that even lighting can hit your chassis without harm. If you live in an area where there are no thunderstorms (Southern California), don't bother. Just use a two terminal receptacle.:-)
Mariss  |