Power off and magnetic contactor (MC)
(1) Inverter primary side magnetic contactor (MC)
On the inverter primary side, it is recommended to provide an MC for the following purposes.
(Refer to page 3 for selection.)
To release the inverter from the power supply when the inverter protective function is activated or the drive
becomes faulty (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 electrical-discharge resistor can be prevented if a regenerative brake transistor is damaged
due to insufficient heat capacity of the electrical-discharge resistor and excess regenerative brake duty.
To prevent any accident due to an automatic restart at restoration of power after an inverter stop made by a
To rest the inverter for an extended period of time
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.
To separate the inverter from the power supply to ensure safe maintenance and inspection work
Since the MC on the inverter primary side is used for the above purposes, they correspond to the standard
duties. Therefore, when making an emergency stop during running, select a JEM1038 class AC3 MC for the
inverter input side currents.
The MC may be switched on/off to start/stop the inverter. However, since repeated inrush currents at power-on will shorten the
life of the converter circuit (switching life is about 100,000 times), frequent starts and stops must be avoided. Turn on/off the
inverter start controlling terminals (STF, STR) to run/stop the inverter.
(2) Handling of secondary side magnetic contactor
In principle, do not provide a magnetic contactor between the inverter and motor and switch it from off to on
during operation. If it is switched on during inverter operation, a large inrush current may flow, stopping the
inverter due to overcurrent shut-off. 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.
Inverter Start/Stop Circuit Example
As shown on the right, always use the start
signal (turn on/off terminals STF, STR-SD) to
start/stop the inverter.
(Refer to page 29.)
*1. Connect the power supply terminals R1 and S1 to the primary side of the MC to hold an alarm signal when the inverter`s
protective circuit is activated. At this time, remove jumpers across terminals R-R1 and S-S1. (For removal of jumpers,
refer to page 15)
Installation of power factor improving reactor
When the inverter is connected near a large-capacity power transformer (1000kVA or more and wiring length 10m (32.80
feet) max.) or when a power capacitor is to be switched over, an excessive peak current may flow in the power input circuit,
damaging the converter circuit. To prevent this, always install the power factor improving reactor.
* When connecting the DC reactor, remove the jumper across terminals P-P1. The wiring length between the DC reactor and
inverter should be 5m (16.4feet) maximum and minimized. Use the same wire size as that of the power supply wire (R, S, T).
DC reactor (*)
Wiring length (m)