Power-OFF and magnetic contactor (MC)
PRECAUTIONS FOR USE OF THE INVERTER
77
3
3.4
Power-OFF and magnetic contactor (MC)
Inverter input side magnetic contactor (MC)
On the inverter input side, it is recommended to provide an MC for the following purposes:
(Refer to
for selection.)
• To disconnect the inverter from the power supply at activation of a protective function or at malfunctioning of the driving
system (emergency stop, etc.). For example, an MC prevents 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 power restoration 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 motor driving, select an MC regarding the inverter input side current as JEM1038-
AC-3 class rated current.
NOTE
• 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 magnetic contactor must be avoided. Turn ON/OFF the inverter start controlling
terminals (STF, STR) to run/stop the inverter.
Handling of the magnetic contactor on the inverter's output side
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 to switch to a commercial power supply, for example, it is recommended to use the commercial
power supply-inverter switchover function
Pr.135 to Pr.139
(Refer to the FR-F800 Instruction Manual (Detailed)). (The
commercial power supply operation is not available with PM motors.)
Handling of the manual contactor on the inverter's output side
A PM motor is a synchronous motor with high-performance magnets embedded inside. High-voltage is generated at the motor
terminals while the motor is running even after the inverter power is turned OFF. In an application where the PM motor is
driven by the load even after the inverter is powered OFF, a low-voltage manual contactor must be connected at the inverter's
output side.
NOTE
• Before wiring or inspection for a PM motor, confirm that the PM motor is stopped. In an application, such as fan and blower,
where the motor is driven by the load, a low-voltage manual contactor must be connected at the inverter's output side, and
wiring and inspection must be performed while the contactor is open. Otherwise you may get an electric shock.
• Do not open or close the contactor while the inverter is running (outputting).
• Inverter start/stop circuit example
As shown on the left, always use the start
signal (ON or OFF of STF(STR) signal) to
make a start or stop.
Install a stepdown transformer.
To hold an alarm signal when the inverter's
protection circuit is activated, input a 24 V
external power supply across ter24
and SD. (Refer to
Power
supply
MCCB
RA
U
V
A1
B1
C1
W
To the
motor
Inverter
SD
MC
STF/STR
R/L1
S/L2
T/L3
+24
SD
OFF
ON
MC
Stop
Start
RA
MC
Operation preparation
Start/Stop
RA
MC
24 V
External
power
supply
T
∗1
∗2
