Electrical Grounding Method for CNC Machine Help Required

Earth-to-neutral volts is more usually an indicator of out-of-balance currents on the supply phases, though 22-24 volts is a bit high. Chances are that the red phase is carrying a lot more current that the yellow or the blue (UK terminology). Maybe a load of lighting or single phase outlets are connected mainly to the red phase and not spread across the others? If so, then some effort might be needed at local distribution boards to address the problem.

What was the result of the earth loop impedance test for this particular piece of equipment? Can this test establish that the earthing arrangements are satisfactory despite the high neutral volts?

Is the outlet a dedicated circuit? Isolated? A separate neutral with dedicated ground back to the panel? Your neutral voltages sounds like a shared neutral.

Good luck,

James

I've read the other comments so far, but don't see one I completely agree with. I'll make an assumption (please forgive me) about you setup; your measurement was taken between the neutral at the machine and the metallic structure of the machine itself or some point like it - "equipment ground". If this is the case, there can be one of several problems.

1) The equipment itself is not properly bonded to the building grounding system. A high impedance connection within this path could explain these readings, especially if the machine was energized "on" when this reading was taken.

2) Voltage drop within the electrical system feeding the machine. The neutral should be bonded to the ground where the electrical service enters your building, and this is typically where the earth grounding system is connected. Depending on the load within your electrical system in combination with imbalance in a three phase system and the distance from your service, any voltage drop on a neutral would show up as a voltage between the neutral and ground where the equipment is.

3) Bad bond between the neutral and the ground at your point of service.

Take measurements at more locations about your facility between neutrals and grounds at other pieces of equipment. Note there location with respect to their distance from their service (feed length through wire).

Does the voltage decrease as you get closer to your service? Look at #2.

Is this problem only seen in this location? Look at #1

Does the voltage remain roughly the same from location to location, or is still significant even close to or at your service? Look at #3

Hope this helps....