Planning the electrical installation
46
Selecting the power cables
General rules
Dimension the mains (input power) and motor cables according to local
regulations:
• The cable must be able to carry the drive load current. See chapter Technical
data for the rated currents.
• The cable must be rated for at least 70
°C maximum permissible temperature of
conductor in continuous use. For US, see Additional US requirements.
• 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 VAC cable is accepted for up to 500 VAC. 750 VAC cable is accepted for up
to 600 VAC. For 690 VAC rated equipment, the rated voltage between the
conductors of the cable should be at least 1 kV.
For drive frame size R5 and larger, or motors larger than 30 kW (40 HP),
symmetrical shielded motor cable must be used (figure below). A four-conductor
system can be used up to frame size R4 with up to 30 kW (40 HP) motors, but
shielded symmetrical motor cable is recommended.
A four-conductor system is allowed for input cabling, but shielded symmetrical cable
is recommended. To operate as a protective conductor, the shield conductivity must
be as follows when the protective conductor is made of the same metal as the phase
conductors:
Compared to a four-conductor system, the use of symmetrical shielded cable
reduces electromagnetic emission of the whole drive system as well as motor
bearing currents and wear.
The motor cable and its PE pigtail (twisted shield) should be kept as short as
possible in order to reduce electromagnetic emission.
Cross-sectional area of the phase
conductors
S (mm
2
)
Minimum cross-sectional area of the
corresponding protective conductor
S
p
(mm
2
)
S < 16 S
16 < S <
35 16
35 < S S/2
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