2.2 Wiring
2-10
2.2.4 Precautions for long wiring (between inverter and motor)
(1) When multiple motors are connected to one inverter, the wiring length is the total of all wire lengths.
(2) Precautions shall be taken for high frequency leak current when the wiring length from the inverter to the
motor is long, in this case the high frequency current may flow through the stray capacitance between the
wires with various phases. The effect may cause the inverter to become overheated, or trip due to
overcurrent. Leak current may increase and the accuracy of the displayed current may not be ensured.
Depending on the conditions, excessive leak current may damage the inverter. To avoid the above problems
when directly connecting an inverter to a motor, keep the wiring distance 50 m (164 ft) for inverters
FRN0020E2■-2/ FRN0012E2■-4 /FRN0011E2■-7 or below, and below 100 m (328 ft) for inverters
FRN0030E2■-2/ FRN0022E2■-4 or above.
To operate with longer wiring lengths than the ones above mentioned, reduce the carrier frequency or use an
output circuit filter (OFL--A).
When multiple motors are operated in parallel connection configuration (group operation), and especially
when shielded cables are used in the connections, the stray capacitance to ground is large. Reduce the
carrier frequency or use output circuit filters (OFL--A).
Without output circuit filter With output circuit filter
When the output circuit filter is used, the total wiring length should be below 400 m (1312ft) in case of using
V/f control.
For motors with encoders, the wiring length between the inverter and motor should be below 100 m (328ft).
The restriction comes from the encoder specifications. For distances beyond 100 m (328ft), insulation
converters should be used. Please contact Fuji Electric when operating with wiring lengths beyond the upper
limit.
(3) Precautions on the surge voltage when driving the inverter (especially for 400 V series motor)
When motors are driven by inverters using the PWM method, the surge voltage generated by the switching of
the inverter elements is added to the output voltage and is applied onto the motor terminals. Especially when
the motor wiring length is long, the surge voltage can cause insulation degradation in the motor. Please
perform one of the countermeasures shown below.
Use motor with insulation enhancement (Fuji’s standard motors have insulation enhancements)
Connect a surge suppression unit on the motor side (SSU50/100TA-NS)
Connect an output circuit filter (OFL--A) to the inverter output side (secondary side)
Reduce the wiring length from the inverter to the motor to less than 10 to 20 meters (33 to 66ft).
(4) When output circuit filters are attached to the inverter or when the wiring length is long, the voltage applied to
the motor will decrease due to the voltage drop caused by the filter or wiring. In these cases, current
oscillation and lack of torque may occur due to insufficient voltage.
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