Earthing?

[JAZZCNC]

A couple of questions regarding earthing in a control box
I'm going to run the screened 4 core wire from steppers to sockets on the metal case and run the screened wire from the inside of the the case (soldered pins on the stepper connector insulated with heat shrink) is it sensible to cover the inside of the socket with copper tape as a screen and to continue the screen continuity?

It's not that critical really but won't hurt if you want to go to that much trouble.

Would I be right in thinking that as the case is earthed I won't need an extra wire from the connector to the bus bar ? I'm going to use a bus bar to connect the earth wires (star earthing) should I bolt the bus bar to the case or insulate it?

Bolt the Bus bar to Cabinet and run all screen wires back to this. Because case is Earth via bus bar then won't need wire from connector body if that's what you mean.

The switching power supply has a metal case I assume as it will be bolted to the case it doesn't need an extra earth wire. I assume all metal cased items such as stepper drivers are earthed by the mounting bolts, or is it better to insulate them and run extra earths to the bus bar.

Just bolt them down to the case.

One last thing is that the boxes holding the connections from the steppers are plastic. Is it worth screening the inside of the boxes but having no electrical contact to the machine frame so that the earthing is only connected at the busbar. I hope this makes sense.

No they will be fine. Don't over complicate things because you can easily introduce problems in your attempts to avoid issues. All you need to do is run all Screens and Earth's back to Star point. If you introduce extra Earth wires etc you can easily create ground loops.

Mains things are.
Shields & earths back to Star point.
Stepper sheilds Earthed at star point only not motor end.
Run all signals wires far away from Mains voltage wires as possible.

[the great waldo]

Thanks Jazz
As the screen for the steppers is connected at the socket via the chassis should I leave both ends of the screen unconnected or is it better to run the driver end of the screen to the bus bar?
Thanks again
Andrew

[Clive S]

Thanks Jazz
As the screen for the steppers is connected at the socket via the chassis should I leave both ends of the screen unconnected or is it better to run the driver end of the screen to the bus bar?
Thanks again
Andrew

Others might have a different view but I have done it like you and grounded the screens at the sockets and the plugs. But then I connected a ground wire bolted to the panel close to the sockets and ran that to the star point.

Then you don't ground the other ends of the cable ie at the driver or motors

[the great waldo]

Thanks Clive.
Just for other forumites make sure there is continuity on the chassis holes for the sockets. On my box only one socket made a connection, all the others were insulated by the case coating/finish. This needs to be corrected.
Cheers.
Andrew

[Neale]

Thanks Clive.
Just for other forumites make sure there is continuity on the chassis holes for the sockets. On my box only one socket made a connection, all the others were insulated by the case coating/finish. This needs to be corrected.
Cheers.
Andrew

I'm also using an epoxy finish steel cabinet, and don't trust any mounting bolts to earth to the cabinet. I've used ground wires from sockets back to the star point, which is a stud welded to the inside of the cabinet.

[Clive S]

I'm also using an epoxy finish steel cabinet, and don't trust any mounting bolts to earth to the cabinet. I've used ground wires from sockets back to the star point, which is a stud welded to the inside of the cabinet.

Yes I should have said that as I have also done the same thing with the mains earth to the star point.

[m_c]

The key thing with grounding, is to avoid ground loops, which you potentially create anytime a screen had more than one ground connection.

However, in power wiring, ground loops aren't likely to be a problem. The point of grounding in power wiring is to contain noise. A ground loop there is unlikely to cause any problems. A prime example is if you wire up a VFD as per most manufacturers recommendations, you ultimately create a ground loop in the wiring, as the motor is likely to be grounded through the machine.

It's in signal wiring, especially low voltage i.e. 5V, where ground loops are far more likely to cause problems.