Precautions When Using Peripheral Devices; Selecting And Installing A Ground Fault Interrupter Or Molded-Case Circuit Breaker; Using A Magnetic Contactor On The Power Supply Side; Using A Magnetic Contactor On The Motor Side - YASKAWA Varispeed G7 Series Instruction Manual

Precautions when Using Peripheral Devices


Selecting and Installing a Ground Fault Interrupter or Molded-Case
Circuit Breaker
A ground fault interrupter (ELCB) is recommended as a general rule to protect Inverter wiring and to prevent
secondary damage when a fault occurs. A molded-case circuit breaker (MCCB) can also be used if permitted
by the power system. We recommend that you select an ELCB designed for Inverters (one with high-fre-
quency countermeasures). The MCCB to select depends on the Inverter's power supply-side power factor
(which depends on the power supply voltage, output frequency, and load). Refer to page 2-4 for the standard
settings. Select an MCCB with a rated current that is 1.5 to 2 times higher than the rated current of the Inverter
in order to avoid nuisance trip caused by harmonics in the drive input current.


Using a Magnetic Contactor on the Power Supply Side

Use a magnetic contactor (MC) to ensure that power to the Inverter can be completely shut off when neces-
sary. The MC should be wired so that it opens when a fault output terminal is triggered.
Avoid switching the magnetic contactor more frequently than once every 30 minutes, even when a magnetic
contactor has been installed on the power supply side to prevent accidents due to automatic restarts when the
power has been restored after a power loss, including momentary power losses (Frequent switching can cause
damage to the Inverter.) Automatic restarts are not performed for Digital Operator operation, so operation can-
not be started with the magnetic contactor. Operation can be stopped with the power supply-side magnetic
contactor, but the motor will coast to a stop without using the Inverter's regenerative braking mechanism. If
the Braking Unit or the Braking Resistor Unit is used, program the sequence so that the magnetic contactor is
turned OFF by the Braking Resistor Unit's thermal overload protector contact.


Using a Magnetic Contactor on the Motor Side

Never turn the magnetic contactor ON or OFF during operation when connected between the Inverter and
motor. If the magnetic contactor is turned ON while the Inverter is operating, a large inrush current will be cre-
ated and the overcurrent protection in the Inverter will operate. When using a magnetic contactor to switch to
a commercial power supply, always stop the Inverter and motor before operating the magnetic contactor. Refer
to page 6-65 for information on switching during operation.
If countermeasures for momentary power loss are required and a magnetic contactor will be used, use a
delayed-release magnetic contactor.


Installing a Thermal Overload Relay

The Inverter has an electronic thermal protection function to protect the motor from overheating. If, however,
more than one motor is operated with one Inverter or a multi-polar motor is used, always install a thermal
relay (THR) or thermal overload protector between the Inverter and the motor. In this case, set L1-01 (Motor
Protection Selection) to 0 (Disabled), and set the thermal relay or thermal overload protector to 1.0 times the
motor nameplate value at 50 Hz and 1.1 times the value at 60 Hz.
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