Mitsubishi Electric FR-D720S-008SC Original Instruction page 20

PRECAUTIONS FOR USE OF THE INVERTER
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 10-5.
Provide electrical and mechanical interlocks for MC1 and MC2 which are
used for bypass operation.
When the wiring is incorrect or if there is a 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.
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 a MC for the following purposes. (Refer to the Instruction Manual.)
– 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.
Handling of inverter output side magnetic contactor
Switch the magnetic contactor between the inverter and motor only when both the inverter and motor are at a stop. When the
magnetic contactor is turned ON while the inverter is operating, overcurrent protection of the inverter and such will activate.
When MC is provided for switching to the commercial power supply, for example, switch it ON/OFF after the inverter and motor
have stopped.
Instructions for overload operation
When performing operation of frequent start/stop of the inverter, increase/decrease in the temperature of the transistor
element of the inverter may repeat due to a continuous flow of large current, shortening the life from thermal fatigue. Since
thermal fatigue is related to the amount of current, the life can be increased by reducing bound current, starting current, etc.
Decreasing current may increase the life. However, decreasing current will result in insufficient torque and the inverter may not
start. Therefore, increase the inverter capacity to have enough allowance for current.
Make sure that the specifications and rating match the system requirements.
When the motor speed is unstable, due to change in the frequency setting signal caused by electromagnetic noises from the
inverter, take the following measures when applying the motor speed by the analog signal.
– Do not run the signal cables and power cables (inverter I/O cables) in parallel with each other and do not bundle them.
– Run signal cables as far away as possible from power cables (inverter I/O cables).
– Use shielded cables as signal cables.
– Install a ferrite core on the signal cable (Example: ZCAT3035-1330 TDK).
14
Power
supply
Undesirable Current
Inverter
Interlock
M
3~