Is this normal?

[Pete147]

Controller build - 3 axis cnc router

In my build i have a central Earth Grounding point where all my earth connections run to.
I also have a separate central point for my DC common ground connections.

The build is complete and up until now there has not been any continuity between the two points listed above, but when I plug the VGA cable of my monitor into the control board, my central Earth Ground point and central DC Common point become connected.

Note: This is due to the VGA socket on the control board being grounded to the control board Ve- terminals and the VGA monitor cord being grounded to the Earth Ground wire in my monitor's power cord. So the connection is being made within the wall sockets which in turn link my two distribution blocks within the cabinet.

Can anyone tell me if this is normal? Can a ground loop occur if the central Earth Ground point is connected to the central Common ground point?

[JAZZCNC]

Need more info on the controller because don't understand why you would be connecting a VGA monitor cable directly to a controller.?

In a normal CNC controller that uses a PC, you should never ground the PC case to the controller's ground because you create a ground loop. So if you have the PC case connected to the controller's ground simply remove it.

[Pete147]

The controller is a MASSO so no PC involved. The Masso is mounted inside the Control unit and has it's own VGA port.

[JAZZCNC]

The controller is a MASSO so no PC involved. The Masso is mounted inside the Control unit and has it's own VGA port.

Never used this controller so can't advise on it really, I suggest you contact MASSO directly and ask the question.

[Neale]

You have all your DC connections taken to one point. You have earth connections (presumably cable screens and similar) taken to another point, and I'm guessing that this is connected to the control box metalwork, machine frame, etc, and includes the external mains earth. If these two points are ONLY connected via the VGA cable and monitor, then there isn't a loop. A loop means that current can get between any two points by two different routes. In your case, there is only one route between two points. However, what this means in terms of interference rejection (which is why you usually try to avoid ground loops) is pretty unpredictable.

Personally, I have combined DC grounds and all the screen and protective earths at one single point. But the only cables leaving my cabinet are to items on the machine (motors, etc) which are isolated, the mains cable itself with its protective earth taken to the common point, and the ethernet cable to the PC - and ethernet has ground isolation built-in, which is one of its advantages. I would be inclined to connect your two grounds together in the cabinet if only to ensure that there is a solid and reliable grounding throughout. I don't like the idea of a random "is it/isn't it connected" situation depending on a VGA cable.

[Pete147]

I would be inclined to connect your two grounds together in the cabinet if only to ensure that there is a solid and reliable grounding throughout. I don't like the idea of a random "is it/isn't it connected" situation depending on a VGA cable.

I will do this... cheers Neale