A.2.5 Motor overload protection
When using the electronic thermal relay function as motor overload protection, set the rated motor current to Pr. 9 "Elec-
tronic thermal O/L relay".
Electronic thermal relay function operation characteristic (LD rating)
Pr. 9 = 50 % setting of
Inverter output current [%]
(% to the inverter rated current)
The internal accumulated heat value of the electronic thermal relay function is reset by inverter power reset and reset
signal input. Avoid unnecessary reset and power-OFF.
When using multiple motors with one inverter, or using a multi-pole motor or a specialized motor, provide an external
thermal relay (OCR) between the inverter and motor. And for the setting of the thermal relay, add the line-to line leakage
current to the current value on the motor rating plate (details in the FR-F800 Instruction Manual).
For low-speed operation where the cooling capability of the motor reduces, it is recommended to use a thermal
protector or thermistor-incorporated 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 an external thermal relay.
Motor over temperature sensing is not provided by the drive.
Pr. 9 = 100 % setting of
Region on the right of
Region on the left of
Characteristic when electronic
thermal relay function for
motor protection is turned OFF
(Pr. 9 = 0 (A))
This function detects the overload (overheat) of the
motor, stops the operation of the inverter's output tran-
sistor, and stops the output. (The operation character-
istic is shown on the left.)
When using the Mitsubishi Electric constant-torque
motor set one of "1", "13" to "16", "50", "53", "54" in
Pr. 71. This provides a 100% continuous torque char-
acteristic in the low-speed range. Set the rated current
of the motor in Pr. 9.
When 50% of the inverter rated output current (current
value) is set in Pr. 9.
The % value denotes the percentage to the inverter rated
output current. It is not the percentage to the motor rated
When you set the electronic thermal relay function
dedicated to the Mitsubishi Electric constant-torque motor,
this characteristic curve applies to operation at 6 Hz or
Transistor protection is activated depending on the
temperature of the heatsink. The protection may be
activated even with less than 120% depending on the