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.