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Selecting the power cables
General rules
Select the input power and motor cables according to local regulations:
•
Select a cable capable of carrying the drive nominal current.
•
Select a cable rated for at least 70
conductor in continuous use.
•
The inductance and impedance of the PE conductor/cable (grounding wire) must be
rated according to permissible touch voltage appearing under fault conditions (so that
the fault point voltage will not rise excessively when a ground fault occurs).
•
600 V AC cable is accepted for up to 500 V AC. 750 V AC cable is accepted for up to
600 V AC. For 690 V AC rated equipment, the rated voltage between the conductors
of the cable should be at least 1 kV.
Use symmetrical shielded motor cables. Ground motor cable shields 360° at both ends.
Keep the motor cable and its PE pigtail (twisted shield) as short as possible to reduce
high-frequency electromagnetic emissions.
Note: When continuous metal conduit is employed, shielded cable is not required. The
conduit must have bonding at both ends.
A four-conductor system is allowed for input cabling, but shielded symmetrical cable is
recommended.
Compared to a four-conductor system, the use of symmetrical shielded cable reduces
electromagnetic emission of the whole drive system as well as the stress on motor
insulation, bearing currents and wear.
The protective conductor must always have an adequate conductivity. The table below
shows the minimum cross-sectional area related to the phase conductor size according to
IEC 61439-1 when the phase conductor and the protective conductor are made of the
same metal.
Cross-sectional area of the phase
conductors
2
S (mm
S < 16
16 < S < 35
35 < S < 400
400 < S < 800
°
Minimum cross-sectional area of the
corresponding protective conductor
)
Guidelines for planning the electrical installation 63
°
C (158
F) maximum permissible temperature of
2
S
(mm
)
p
S
16
S/2
200
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