Mitsubishi Electric 800 Series Instruction Manual page 319

(H) Protective function parameter
Electronic thermal O/L relay operation characteristic for induction motor
(Pr.9, E.THM)
• This function detects the overload (overheat) of the motor and trips the inverter by stopping the operation of the transistor at
the inverter output side.
• Set the rated current (A) of the motor in Pr.9. (If the motor has both 50 Hz and 60 Hz ratings and the Pr.3 Base frequency
is set to 60 Hz, set to 1.1 times the 60 Hz rated motor current.)
• Set "0" in Pr.9 to avoid activating the electronic thermal O/L relay function; for example, when using an external thermal
relay for the motor. (Note that the output transistor protection of the inverter is activated. (E.THT))

When setting Pr.9 to a value (current value) of 50% of the inverter rated current

The % value denotes the percentage to the inverter rated current. It is not the percentage to the rated motor current.

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.
NOTE
• The internal accumulated heat value of the electronic thermal relay function is reset to the initial value by the inverter's power
reset and 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
operation. Use a thermal protector or a motor with built-in thermistor.
• The protective characteristic of the electronic thermal O/L relay is degraded when there is a large difference in capacity
between the inverter and motor, and when the set value is small. In such case, use an external thermal relay.
• A dedicated motor cannot be protected by an electronic thermal O/L relay. Use an external thermal relay.
• The transistor protection thermal O/L relay is activated early when the Pr.72 PWM frequency selection setting is increased.
• When using a PM motor, set the free thermal parameters (Pr.600 to Pr.604) in accordance with the motor characteristic.
318
PARAMETERS
Pr. 9 = 50% setting Pr. 9 = 100% setting
1, 2
of inverter rating∗ of inverter rating∗
70
30Hz
or more
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
52.5% 105%
100
50
Inverter output power (%)
(% to the inverter rated current)
1, 2
30Hz or more
20Hz
Operation region
Region on the right of
10Hz
characteristic curve
6Hz
Non-operation region
Region on the left of
0.5Hz
characteristic curve
Characteristic when
electronic thermal relay
function for motor
protection is turned off
(When Pr. 9 setting is 0(A))
Range for
the transistor
∗3
protection
150 230
page 68.) The cooling effect of the motor drops during low-speed