Mitsubishi Electric 700 Series Installation Manualline page 22

APPENDIX
A.2.4 Motor overload protection
The inverter FR-A 740 is equipped with an internal UL certified electronic motor overload protection.
When using the electronic thermal relay as motor overload protection, set the rated motor current to Pr.9 Electronic thermal
O/L relay.
Electronic thermal relay function characteristic
Pr. 9 = 50% setting of
*1, 2
inverter rating
*3
or more
Inverter output power (%)
(% to the rated input current)
CAUTION
Protective function by electronic thermal relay function is reset by inverter power reset and reset signal input. Avoid unnecessary reset
and power-off.
When multiple motors are operated by a single inverter, protection cannot be provided by the electronic thermal relay function. Install
an external thermal relay to each motor.
When the difference between the inverter and motor capacities is large and the setting is small, the protective characteristics of the
electronic thermal relay function will be deteriorated. In this case, use an external thermal relay.
A special motor cannot be protected by the electronic thermal relay function. Use a external thermal relay.
18
Pr. 9 = 100% setting of
*1, 2
inverter rating
*3
or more
Operation: left side of
characteristic curve
Non-Operation
(motor protection):
right side of charac-
teristic curve
Characteristic when
electronic thermal relay
function for motor
protection is turned OFF
(Pr. 9 = 0 (A))
For transistor
protection electronic
thermal relay
function
This function detects the overload (overheat) of the
motor, stops the operation of the inverter's output
transistor, and stops the output.
When using the Mitsubishi constant-torque motor set "1"
or any of "13" to "18", "50", "53", "54" in Pr. 71. This
provides a 100% continuous torque characteristic in the
low-speed range. Set the rated current of the motor in
Pr. 9.
*1
When a value 50% of the inverter rated output current (current value)
is set in Pr. 9.
*2
The % value denotes the percentage to the inverter rated output
current. It is not the percentage to the motor rated current.
*3
When you set the electronic thermal relay function dedicated to the
Mitsubishi constant-torque motor, this characteristic curve applies to
operation at 6Hz or higher.