Appendix C
162
Shield
Jacket
Insulation
Conductor
PE
PEconductorandshield
Jacket
Insulation
Conductor
Jacket
Insulation
Conductor
PE
Symmetrical shielded cable
Four conductor cable
-
Note:
A separate PE conductor is required if the conductivity of the cable shield is not sufficient for
the purpose.
To function as a protective conductor, the shield must have the same cross-sectional area as the
phase conductors when they are made of the same metal.
To effectively suppress radiated and conducted radio-frequency emissions, the 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. The better and tighter the shield is,
the lower the emission level and bearing currents.
Cross-section of the cable
Insulation course
Wire screen