Planning the electrical installation 37
Alternative power cable types
Motor cables (also recommended for supply cabling):
Allowed for AC power cabling
Motor cable shield
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 aluminium 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, the lower the emission level and bearing
currents.
Symmetrical shielded cable: three phase
conductors and a concentric or otherwise
constructed PE conductor, and a shield.
Check with local / state / country electrical
codes for allowance.
Note: A separate PE conductor is required
if the conductivity of the cable shield is not
sufficient for the purpose.
A four-conductor system: three phase
conductors and a protective conductor.
1 Insulation jacket
2 Copper wire screen
3 Helix of copper tape or copper wire
4 Inner insulation
5 Cable core
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