52 Planning the electrical installation
Motor cable shield
If 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 section General rules
above, or IEC 61439-1.
To effectively suppress radiated and conducted radio-frequency emissions, the cable
shield conductivity must be at least 1/10 of the phase conductor conductivity. The
requirements are easily met with a copper or aluminum shield. The minimum
requirement of the motor cable shield of the drive is shown below. It consists of a
concentric layer of copper wires with an open helix of copper tape or copper wire. The
better and tighter the shield, the lower the emission level and bearing currents.
Additional US requirements
Use type MC continuous corrugated aluminum armor cable with symmetrical grounds
or shielded power cable for the motor cables if metallic conduit is NOT USED. For the
North American market, 600 V AC cable is accepted for up to 500 V AC. 1000 V AC
cable is required above 500 V AC (below 600 V AC). For drives rated over 100
amperes, the power cables must be rated for 75
°C (167 °F).
Conduit
Couple separate parts of a conduit together: bridge the joints with a ground conductor
bonded to the conduit on each side of the joint. Also bond the conduits to the drive
enclosure and motor frame. Use separate conduits for input power, motor, brake
resistor, and control wiring. When conduit is employed, type MC continuous
corrugated aluminum armor cable or shielded cable is not required. A dedicated
ground cable is always required.
Note: Do not run motor wiring from more than one drive in the same conduit.
1 Sheath
2 Copper wire shield
3 Helix of copper tape or copper wire
4 Filling
5 Cable conductors
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