VLT ® 2800 Series■ Earthing of screened/armoured control cablesIn general control cables must be screened/armoured,and the screen must be connected to the unit’s metalcabinet with a cable clamp at each end.The drawing below shows the correct way to performthe earthing, and what to do when in doubt.1. Correct earthingControl cables and cables for serialcommunication must be attached with cableclamps at both ends to ensure maximumpossible electrical contact.2. Incorrect earthingDo not use twisted screen ends thatare plaited together (pigtails), as these increasescreen impedance at higher frequencies.3. Protection with respect to earthpotential between PLC and VLTIf the earth potential between the VLTfrequency converter and the PLC (etc.) is different,electric noise may occur that will disturb the wholesystem. This problem can be solved by fitting anequalising cable, to be placed next to the controlcable. Minimum cable cross-section: 16 mm 2 .4. In the event of a 50/60 Hz earth loopIf very long control cables are used, 50/60 Hzearth loops can arise, and these can interferewith the whole system. This problem is resolvedby attaching one end of the screen to the earthvia a 100 nF capacitor (short pin length).MG.28.E9.02 - VLT is a registered Danfoss trademark46
