Motor overload protection
When using the electronic thermal relay function as motor overload protection, set the rated motor current in Pr.9 Electronic
thermal O/L relay.
This function detects the overload of the motor and shut off the inverter output by stopping the operation of the transistor at the
inverter output side. (The operation characteristic is shown below.)
• When using the Mitsubishi Electric constant-torque motor
Set "1, 13 to 16" in Pr.71. (This setting enables the 100% constant-torque characteristic in the low-speed range.)
Set the rated motor current in Pr.9.
When setting Pr.9 to a value (current value) of 50% of the inverter rated output current.
The % value denotes the percentage to the inverter rated current. It is not the percentage to the rated motor current.
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 higher.
Transistor protection is activated depending on the temperature of the heat sink. The protection may be activated even with less than 150%
depending on the operating conditions.
• The internal accumulated heat value of the electronic thermal O/L relay is reset to the initial value by the inverter's power reset
or reset signal input. Avoid unnecessary reset and power-OFF.
• Install an external thermal relay (OCR) between the inverter and motors to operate several motors, a multi-pole motor or a
dedicated motor with one inverter. When setting an external thermal relay, note that the current indicated on the motor rating
plate is affected by the line-to-line leakage current. (Refer to the Instruction Manual (Detailed).)
• The cooling effect of the motor drops during low-speed operation. Use a thermal protector or a motor with built-in thermistor.
• 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 such case, use an external thermal relay.
• A dedicated motor cannot be protected by the electronic thermal relay. Use an external thermal relay.
• Motor over temperature sensing is not provided by the drive.
• The electronic thermal memory retention function is not provided by the drive.
Operational characteristic of the electronic thermal relay function
Pr.9 = 50% setting
of inverter rating
Inverter output power (%)
(% to the inverter rated current)
Pr.9 = 100% setting
of inverter rating
Region on the right of
Region on the left of
electronic thermal relay
function for motor
protection is turned off
(When Pr.9 setting is 0(A))
7.3 Instructions for compliance with the EU Directives