14
Installation and maintenance - Three-phase induction motors
4850 en - 2018.11 / f
ASSEMBLY
2.5.2 - Cross-section of the power supply cables
The higher the current, the greater the voltage drop in the
cables (standard NFC 15.100 or end user’s national standard).
The voltage drop should therefore be calculated
for the
starting current
to see if this is suitable for the application.
If the most important criterion is the starting torque (or starting
time), the voltage drop should be limited to 3% maximum (the
equivalent of a loss of torque of around 6 to 8%).
The chart below can be used to select the conductors according
to the length of the supply cables and the starting current, in
order to limit the voltage drop to 3% maximum.
This table does not allow the installer to dispense with checking the protective systems.
For motors with flying leads, the power supply cable must not be used for handling.
2.5.3 - Connection of the motor-drive unit
When controlling an induction motor by means of a variable
speed drive, certain rules must be adhered to in order to
guarantee correct system performance.
For variable speed applications, follow the recommendations
outlined in the good practice guide for Motor and drive
packages ref. 5626.
1
2
3
4
5 6 7 8 9 10
2
3
4
5 6 7 8 9 100
2
3
4
5
2
3
4
5
6 7 8 9 1000
10
20
30
40
50
60
70
80
90
100
200
300
400
500
600
700
800
900
1000
Length in m
Maximum voltage drop 3 % (3-phase circuits - copper cable)
Current in amps
Starting current
1 1.5 2.5 4 6
10 16
35 50 75 90
25
Conductor cross-section