Planning the electrical installation 75 Motor cable shieldIf the motor cable shield is used as the sole protective earth conductor of the motor,make sure that the conductivity of the shield is sufficient. See subsection Generalrules on page 69, or IEC 61800-5-1. To effectively suppress radiated and conductedradio-frequency emissions, the cable shield conductivity must be at least 1/10 of thephase conductor conductivity. The requirements are easily met with a copper oraluminum shield. The minimum requirement of the motor cable shield of the drive isshown below. It consists of a concentric layer of copper wires with an open helix ofcopper tape or copper wire. The better and tighter the shield, the lower the emissionlevel and bearing currents. Additional US requirementsUse type MC continuous corrugated aluminum armor cable with symmetrical groundsor shielded power cable for the motor cables if metallic conduit is not used. For theNorth American market, 600 V AC cable is accepted for up to 500 V AC. 1000 V ACcable is required above 500 V AC (below 600 V AC). For drives rated over 100amperes, the power cables must be rated for 75 °C (167 °F).ConduitCouple separate parts of a conduit together: bridge the joints with a ground conductorbonded to the conduit on each side of the joint. Also bond the conduits to the driveenclosure and motor frame. Use separate conduits for input power, motor, brakeresistor, and control wiring. When conduit is employed, type MC continuouscorrugated aluminum armor cable or shielded cable is not required. A dedicatedground cable is always required.Note: Do not run motor wiring from more than one drive in the same conduit.1 Insulation jacket2 Copper wire screen3 Helix of copper tape or copper wire4 Inner insulation5 Cable core123 4 5
