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sparkjon69:
Can you give us some EGC current values and under what machine conditions?
A general comment about any small CNC or similar machine. This kind of machine consists of a big chunk of cast iron and heavy steel all attached together as one unit with a heavy steel electrical cabinet. This whole combination is a rather low electrical impedance viewed from many different points on the machine.
Within the electrical enclosure is an EGC terminating point. In a HAAS machine this is a bus bar at the top inside of the electrical cabinet and bonded to the electrical cabinet. Any additional grounding conductors would be expected to be terminated at this same bus bar.
Make no electrically conductive connections to this machine except the NEC required EGC (as defined by NEC) and the hot (ungrounded) power wires. Support the machine on insulators. This creates a condition where there is no ground loop. If there is any EGC current, then it is the result of HAAS internal circuits. If this EGC current is greater than what it should be, then there is a failure within the HAAS machine. From my limited measurements so far this current should be less than 1 A.
Put the machine on a concrete floor and this might create a very minor ground loop path. Add a metallic air line system to the machine and there should be a good moderately low impedance ground loop path. Add auxiliary equipment and various other conductive ground loop paths may be created.
Go back to a basic machine sitting on insulators and the one required EGC connection. Add a supplemental ground rod at the machine and bonded to the machine ground bus bar.
Now a ground loop has been created. Suppose this causes 10 A of EGC current. This current only flows thru the EGC wire, a small section of the ground bus bar, and the wire to the supplemental ground rod. How does that have any affect on any circuits within the CNC machine? It doesn't. There is virtually no voltage drop in the machine, just a very small drop (millivolts) in a small part of the ground bus bar.
Had the supplemental ground rod been terminate at some arbitrary point on the CNC machine frame, then there would be a small voltage drop across some portion of the machine. Again at a 10 A level only millivolts.
What does happen from the ground loop current is an increase of the voltage of the CNC frame relative to remote earth ground. But unless this is from hugh currents and energy sources there is no problem, and then it is the potential of the machine chassis relative to other objects close by that are at remote ground potential, shock hazard. But this does not affect the components within the CNC except as to how the EGC voltage at the machine changes relative to the hot AC lines.
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