Precautions For Use Of The Inverter - Mitsubishi Electric FR-A720-0.4K Instruction Manual

3.5 Precautions for use of the inverter

The FR-A700 series is a highly reliable product, but incorrect peripheral circuit making or operation/handling method
may shorten the product life or damage the product.
Before starting operation, always recheck the following items.
(1) Use crimping terminals with insulation sleeve to wire the power supply and motor.
(2) Application of power to the output terminals (U, V, W) of the inverter will damage the inverter. Never perform such wiring.
(3) After wiring, wire offcuts must not be left in the inverter.
Wire offcuts can cause an alarm, failure or malfunction. Always keep the inverter clean. When drilling mounting holes in
an enclosure etc., take care not to allow chips and other foreign matter to enter the inverter.
(4) Use cables of the size to make a voltage drop 2% maximum.
If the wiring distance is long between the inverter and motor, a main circuit cable voltage drop will cause the motor torque
to decrease especially at the output of a low frequency.
22
Refer to page for the recommended cable sizes.
(5) The overall wiring length should be 500m maximum.
(The wiring length should be 100m maximum for vector control.)
Especially for long distance wiring, the fast-response current limit function may be reduced or the equipment connected to
the inverter output side may malfunction or become faulty under the influence of a charging current due to the stray capacity
of the wiring. Therefore, note the overall wiring length. (Refer to page 25.)
(6) Electromagnetic wave interference
The input/output (main circuit) of the inverter includes high frequency components, which may interfere with the
communication devices (such as AM radios) used near the inverter. In this case, set the EMC filter valid to minimize
interference. (Refer to page 15)
(7) Do not install a power factor correction capacitor, surge suppressor or radio noise filter on the inverter output side.
This will cause the inverter to trip or the capacitor, and surge suppressor to be damaged. If any of the above devices is
installed, immediately remove it.
(8) Before starting wiring or other work after the inverter is operated, wait for at least 10 minutes after the power supply has
been switched off, and check that there are no residual voltage using a tester or the like. The capacitor is charged with high
voltage for some time after power off and it is dangerous.
(9) A short circuit or earth (ground) fault on the inverter output side may damage the inverter modules.
· Fully check the insulation resistance of the circuit prior to inverter operation since repeated short circuits caused by
peripheral circuit inadequacy or an earth (ground) fault caused by wiring inadequacy or reduced motor insulation
resistance may damage the inverter modules.
· Fully check the to-earth (ground) insulation and inter-phase insulation of the inverter output side before power-on.
Especially for an old motor or use in hostile atmosphere, securely check the motor insulation resistance etc.
(10) Do not use the inverter input side magnetic contactor to start/stop the inverter.
Always use the start signal (ON/OFF of STF and STR signals) to start/stop the inverter.
(11) Across P/+ and PR terminals, connect only an external regenerative brake discharge resistor.
Do not connect a mechanical brake.
(12) Do not apply a voltage higher than the permissible voltage to the inverter I/O signal circuits.
Contact to the inverter I/O signal circuits or opposite polarity may damage the I/O devices. Especially check the wiring to
prevent the speed setting potentiometer from being connected incorrectly to short terminals 10E-5.
(13) Provide electrical and mechanical interlocks for MC1 and
MC2 which are used for electronic bypass.
When the wiring is incorrect or if there is an electronic
bypass circuit as shown on the right, the inverter will be
damaged by leakage current from the power supply due to
arcs generated at the time of switch-over or chattering
caused by a sequence error.
(Commercial operation can not be performed with the vector
dedicated motor (SF-V5RU, SF-THY).)

Precautions for use of the inverter

(Refer to page 63)
Power
R/L1 U
supply
S/L2 V
T/L3 W
Undesirable current
Inverter
3
MC1
Interlock
IM
MC2
65