HD65 & HD130 STEPPER DRIVES USER GUIDE 3
Where signal connections pass between units mounted in different enclosures and separately energised from the mains, optical isolation of all communication lines is recommended. It is still desirable that all such isolated systems have their 0v rails directly connected to earth.
Motor leads should be collectively screened if they run close to power switching lines, particularly those driving unsuppressed inductive loads. Whilst noise picked up on the motor leads is unlikely to affect the motor directly, the noise gets coupled back into the drive system and can cause problems as a result.
Contactors and relays feeding inductive loads should be adequately suppressed.