4.2.6 Electronic thermal relay function (Pr. 9, Pr. 48)
Pr. 9 "electronic thermal O/L relay
Pr. 48 "second electronic thermal
O/L relay "
Set the current of the electronic thermal relay function to protect the motor from
overheat. This feature provides the optimum protective characteristics, including
reduced motor cooling capability, at low speed.
*0.1K to 0.75K are set to 85% of the rated inverter current.
• Set the rated current [A] of the motor.
(Normally set the rated current at 50Hz if the motor has both 50Hz and 60Hz rated
• Setting "0" makes the electronic thermal relay function (motor protective function)
invalid. (The inverter's protective function is valid.)
• Set "1" in Pr.71 when using the Mitsubishi constant torque motor. (This provides a
100% continuous torque characteristic in the low-speed region.) Then, set the rated
motor current in Pr. 9.
• Pr. 48 "second electronic thermal O/L relay" is made valid when the RT signal is on.
Note: 1. When two or more motors are connected to the inverter, they cannot be
protected by the electronic overcurrent protection. Install an external
thermal relay to each motor.
2. 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
3. A special motor cannot be protected by the electronic thermal relay function.
Use an external thermal relay.
4. The RT signal serves as the second function selection signal and makes the
other second functions valid. Refer to page 161 for Pr. 180 to Pr. 183 (input
terminal function selection).
0 to 500A, 9999
Pr. 71 "applied motor"
Pr. 180 to Pr. 183
(input terminal function
0 to 500A
9999: Function invalid