Power-OFF and magnetic contactor (MC)
PRECAUTIONS FOR USE OF THE INVERTER
71
3
3.4 Power-OFF and magnetic contactor (MC)
Converter unit input side magnetic contactor (MC)
On the converter unit input side, it is recommended to provide an MC for the following purposes:
(Refer to page 14 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.).
• 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 operation, select an MC regarding the converter unit 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.
• Inverter start/stop circuit example
As shown below, always use the start signal (ON or OFF of STF(STR) signal) to make a start or stop.
When the power supply is 400 V class, install a stepdown transformer.
Connect the power supply terminals R1/L11, S1/L21 of the control circuit to the input side of the MC to hold an alarm signal when the inverter's
protective circuit is activated. At this time, remove jumpers across terminals R1/L11 and S1/L21. (Refer to page 43 for removal of the jumper.)
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. (The commercial power supply operation is not available with
vector control dedicated motors nor 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.
MCCB
Converter
unit
Power
supply
To the
motor
Inverter
Stop
Start
Operation preparation
Start/Stop
P/+
N/-
P/+
N/-
A1
B1
C1
RDA
MC
R/L1
S/L2
T/L3
R1/L11
S1/L21
OFF
ON
MC
RA
MC
RA
MC
RA
U
V
A1
B1
C1
W
SD
STF/STR
R1/L11
S1/L21
X10
SE
SD
T
∗1
∗2 ∗2
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