Inverter with motor needed

Generally I would ideally screen a motor cable at both ends so that the cable screen extends around the teminal housing on the motor and the motor casing. The object being to limit emissions from high current conductors.

For signal cables I generally want to screen one end only to obtain some shielding of my signals from external noise and to avoid ground loops and multiple earth points.

Generally for control gear using low impedance sensors (such as switches and pots) the main thing you are concerned about is EM radiation rather than noise immunity so it doesn't really matter too much unless the neighbors complain.

You have to remember that currents case magnetic fields and voltages cause electric fields so how you ground bond, ground reference and earth protect depends on what you are required to do and what you wish to achieve.

Have a go at building a PA sound system and earth everything at both ends and have a listen to the hum.

Connect your system according to the manufacturers instructions. If it works leave it alone. If you have problems like you cannot hear the test match on long wave or your tacho doesn't work properly then think about changing your arrangement.

regards Martin

I've seen both methods recommended by motor drive manufacturers and ABB certainly count as credible authorities. That looks like a pretty sensible guide from them.

Bottom line is you need to test the final installation for compliance to the required EMC standards (EN55011 for industrial, scientific and medical appliances in the EU). As the manufacturer, you can recommend and sell filters etc that will typically enable the system to meet the requirements but each implementation is different so it's not possible to provide a definitive solution.

You can certainly find problems if you leave one end of the motor screen floating. The screen forms a rather nice undamped half wave stub that will resonate if you provide it with the correct stimulus eg a PWM voltage - I can tell you myself from experience that in that situation, grounding both ends can indeed be very helpful. There should be a separate protective earth anyway (for electrical safety) and usually any sizeable motor will be firmly bolted to a large conductive (and thus earthed) assembly, so the motor isn't going to start flapping up and down (electrically) either way. However, a resonant stub aerial isn't going to do anyone any EMC favours.

Murray