46 Planning the electrical installation
Motor cable shield
To function as a protective conductor, the shield must have the same cross-sectional
area as a phase conductor 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 with an open helix of copper tape. The better and tighter the shield, the lower
the emission level and the bearing currents.
Insulation jacket Copper wire screen Helix of copper tape
Cable core
Inner insulation
Selecting the control cables
It is recommended that all control cables be shielded.
Double-shielded twisted pair cable is recommended for analog signals. For pulse
e
ncoder cabling, follow the instructions given by the encoder manufacturer. Use one
individually-shielded pair for each signal. Do not use a common return for different
analog signals.
Double-shielded cable (Figure a) is the best al
ternative for low-voltage digital signals
but single-shielded twisted multi-pair cable (Figure b) is also usable.
Run analog and digital signals in separate cables.
Never mix 24 VDC and 240 VAC signals in the same cable.
Connection of a motor temperature sensor to the drive
See page 58.
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