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Power-off and magnetic contactor (MC)
3.3 Power-off and magnetic contactor (MC)
(1) Inverter input side magnetic contactor (MC)
On the inverter input side, it is recommended to provide an MC for the following purposes.
(Refer to page 4 for selection.)
1)To release the inverter from the power supply when the fault occurs or when the drive is not functioning (e.g. emergency
stop operation). When cycle operation or heavy-duty operation is performed with an optional brake resistor connected,
overheat and burnout of the discharging resistor can be prevented if a regenerative brake transistor is damaged due to
insufficient heat capacity of the discharging resistor and excess regenerative brake duty.
2)To prevent any accident due to an automatic restart at restoration of power after an inverter stop made by a power failure
3)The control power supply for inverter is always running and consumes a little power. When stopping the inverter for an
extended period of time, powering off the inverter will save power slightly.
4)To separate the inverter from the power supply to ensure safe maintenance and inspection work.
The inverter's input side MC is used for the above purpose, select class JEM1038-AC3 MC for the inverter input side
current when making an emergency stop during normal operation.
(2) 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 an MC is provided for switching to the commercial power supply, for example, switch it on/off after the inverter and
motor have stopped.
REMARKS
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. Turn on/off the inverter start controlling terminals (STF, STR) to run/stop the
inverter.
Inverter start/stop circuit example
As shown on the left, always use the start signal
(ON or OFF across terminals STF or STR-SD) to
make a start or stop.
∗1 When the power supply is 400V class, install a step-down
transformer.
Three-phase AC
power supply
R/L1
S/L2
T/L3
U
V
W
Moto
r
MCCB MC
SD
STF(STR)
A
B
C
RA
OFF
ON
MC
Stop
Operation
RA
MC
Operation preparation
Start/Stop
MC
RA
Inverter
T
*1