72 Guidelines for planning the electrical installation Motor cable shieldIf the motor cable shield is used as the sole protective earth conductor of the motor, makesure that the conductivity of the shield is sufficient. See subsection General rules on page69, or IEC 61800-5-1. To effectively suppress radiated and conducted radio-frequencyemissions, the cable shield conductivity must be at least 1/10 of the phase conductorconductivity. The requirements are easily met with a copper or aluminum shield. Theminimum requirement of the motor cable shield of the drive is shown below. It consists of aconcentric layer of copper wires with an open helix of copper tape or copper wire. Thebetter and tighter the shield, the lower the emission level and bearing currents. Additional US requirementsUse type MC continuous corrugated aluminum armor cable with symmetrical grounds orshielded power cable for the motor cables if metallic conduit is not used. For the NorthAmerican market, 600 V AC cable is accepted for up to 500 V AC. 1000 V AC cable isrequired above 500 V AC (below 600 V AC). For drives rated over 100 amperes, thepower 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, brake resistor,and control wiring. When conduit is employed, type MC continuous corrugated aluminumarmor cable or shielded cable is not required. A dedicated ground cable is alwaysrequired.Note: Do not install motor wiring from more than one drive in the same conduit.Armored cable / shielded power cableSix conductor (3 phases and 3 ground) type MC continuous corrugated aluminum armorcable with symmetrical grounds is available from the following suppliers (trade names inparentheses):• Anixter Wire & Cable (Philsheath)• BICC General Corp (Philsheath)• Rockbestos Co. (Gardex)• Oaknite (CLX).Shielded power cables are available from Belden, LAPPKABEL (ÖLFLEX) and Pirelli.1 Insulation jacket2 Copper wire screen3 Helix of copper tape or copper wire4 Inner insulation5 Cable core123 4 5
