Drivers,BOB and PSU are in a PC case, do i earth the case

[deannos]

Which cable are you referring to? While, in principal if the PSU is built to Class 2 insulation specs it is not necessary to earth it, I would recommend earthing everything. The point of not earthing the screen at both ends is to prevent currents flowing in the screen which could compromise the screening efficiency. If necessary a separate earth conductor could be included. inside the screened cable.

Russell.

The cable is 4 core screened and i have used this to connect the motors to the drivers and also to connect the drivers to the BOB

[russell]

The cable is 4 core screened and i have used this to connect the motors to the drivers and also to connect the drivers to the BOB

If both the drivers and BOB are inside the case they do not need screened cable between them. The screen of the motor cable should be connected to the case and left unconnected at the machine end. Both the machine and the computer case should be earthed via the mains cable.

Russell.