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Mitsubishi Electric FR-F740-00023 Instruction Manual: Precautions For Use Of The Inverter

F700 series.
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3.5 Precautions for use of the inverter

The FR-F700 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.
Refer to page 17 for the recommended cable sizes.
(5) The overall wiring length should be 500m maximum.
Especially for long distance wiring, the fast-response current limit function may decrease or the equipment connected to the
secondary 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 19.)
(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
(Refer to page
(7) Do not install a power factor correction capacitor, surge suppressor or capacitor type 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) For some short time after the power is switched off, a high voltage remains in the smoothing capacitor. When accessing the
inverter for inspection, wait for at least 10 minutes after the power supply has been switched off, and then make sure that
the voltage across the main circuit terminals P/+-N/- of the inverter is not more than 30VDC using a tester, etc.
(9) A short circuit or earth 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 fault caused by wiring inadequacy or reduced motor insulation resistance
may damage the inverter modules.
· Fully check the to-earth insulation and phase to 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) Do not apply a voltage higher than the permissible voltage to the inverter I/O signal circuits.
Application of a voltage higher than the permissible voltage 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.
(12) Provide electrical and mechanical interlocks for MC1 and
MC2 which are used for bypass operation.
When the wiring is incorrect or if there is an electronic
bypass circuit as shown on the right, the inverter will be
damaged when the power supply is connected to the
inverter U, V, W terminals due to arcs generated at the time
of switch-over or chattering caused by a sequence error.
Precautions for use of the inverter
(Refer to page
Undesirable current


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