If you do tie your circuit ground to the case, make sure it is only at a single point, otherwise you can get ground loops and in some cases that can cause noise problems even in digital circuits. Many years ago my home-built computer had such a horrible mess of ground loops that I could hear radio interference on a pocket radio several houses away. Once I removed the ground loops, there was no detectable interference outside the metal cabinet.
If my project has a metal (conductive) case, I connect it directly to the ground terminal of the line cord with high-current wiring (no connectors, splices, etc). As far as I know, the reason consumer and industrial equipment do the same is to provide user protection in case the device gets damaged and the AC line contacts the exposed conductive areas. If that happens, the ground protects you until the circuit-breaker/GFCI trips. But, I dont tie the circuit gnd directly to the case; instead I use about 1 meg of resistance to bleed-off ESD and provide a DC path to GND. Circuit-wise, if you are using an isolated supply there's really no need for your circuit GND to be tied to the earth. Now for high-voltage circuits that have an isolated supply, if your circuit GND is tied directly to the earth, you probably will get shocked if you touch the high-voltage supply, depending upon your body resistance (varies wildly from 500 ohms to about 100K), and possibly additional protection from clothing. However, if your circuit GND has a 1Meg path to earth ground, you may not get shocked at all; even if you touch a 500V supply, the current will be less than 500uA which I think is below the threshold of sensitivity. Where things get tricky is if you are going to connect the device you built to another device, such as a USB port on a computer. If both devices have a low-impedance path from their respective circuit-gnd to the AC power-cord (earth) ground, you will get a ground loop. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/effa0838-26ff-4a98-bcea-902e2992a1c2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
