Mitsubishi Electric FR-F740 EC Instruction Manual page 94

Precautions for use of the inverter
● 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 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.
● Do not use the inverter input side magnetic contactor to start/stop the inverter.
Since repeated inrush currents at power on will shorten the life of the converter circuit
(switching life is about 1,000,000 times), frequent starts and stops of the MC must be
avoided. Always use the start signal (ON/OFF of STF and STR signals) to start/stop the
inverter.
● 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 (10, respectively) and 5.
● Provide electrical and mechanical interlocks for MC1 and MC2 which are used for commer-
cial power supply-inverter switch-over.
When the wiring is incorrect or if there is a commercial power supply-inverter switch-over
circuit as shown below, 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.
Power
supply
● If the machine must not be restarted when power is restored after a power failure, provide
a magnetic contactor in the inverter's input side and also make up a sequence which will
not switch on the start signal.
If the start signal (start switch) remains on after a power failure, the inverter will automatically
restart as soon as the power is restored.
● Inverter input side magnetic contactor (MC)
On the inverter input side, connect an MC for the following purposes (also refer to section
3.1.1):
– To release the inverter from the power supply when a fault occurs or when the drive is
not functioning (e.g. emergency stop operation). For example, MC avoids overheat or
burnout of the brake resistor when heat capacity of the resistor is insufficient or brake
regenerative transistor is damaged with short while connecting an optional brake resistor.
– To prevent any accident due to an automatic restart at restoration of power after an
inverter stop made by a power failure.
– To separate the inverter from the power supply to ensure safe maintenance and
inspection work. If using an MC for emergency stop during operation, select an MC
regarding the inverter input side current as JEM1038-AC-3 class rated current.
4 - 2
M
3~
Undesirable current
Fig. 4-1:
Mechanical interlocks for MC1 and MC2
Operation
I001042E