Mitsubishi Electric FR-A872-E Instruction Manual page 122

 Short circuit ratings
Suitable for use in a circuit capable of delivering not more than 100 kA rms symmetrical amperes, 600 V maximum.
 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 (overheat) 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.)
*1 When setting Pr.9 to a value (current value) of 50% of the inverter rated output current.
*2 The % value denotes the percentage to the inverter rated current. It is not the percentage to the rated motor current.
*3 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 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 configuring 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 (Function).)
• 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.
Operational characteristic of the electronic thermal relay function
Pr.9 = 50% setting
of inverter rating *1, 2
70
30Hz
or more
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
105%
52.5%
50
Inverter output power (%)
(% to the inverter rated current)
Pr.9 = 100% setting
of inverter rating *2
30Hz
Operation region
or more
Region on the right of
characteristic curve
20Hz
Non-operation region
10Hz
Region on the left of
characteristic curve
6Hz
Characteristic when
0.5Hz
electronic thermal relay
function for motor
protection is turned off
(When Pr.9 setting is 0(A))
Range for
the transistor
*3
protection
100
150 230
7. APPENDIX
7.3 Instructions for UL and cUL
1
2
3
4
5
6
7
8
9
10
121