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Mitsubishi Electric FR-F700PJ Instruction Manual Page 56

Air-conditioning inverter.
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(2)
Line-to-line leakage currents
Harmonics of leakage currents flowing in static capacitances between the inverter output cables may operate the external
thermal relay unnecessarily. When the wiring length is long (50m or more) for the 400V class small-capacity model (7.5kW or
less), the external thermal relay is likely to operate unnecessarily because the ratio of the leakage current to the rated motor
current increases.
Line-to-line leakage current data example (400V class)
Motor Capacity
Rated Motor
(kW)
Current (A)
0.4
1.1
0.75
1.9
1.5
3.5
2.2
4.1
3.7
6.4
5.5
9.7
7.5
12.8
Power
supply
Measures
 Use Pr. 9 Electronic thermal O/L relay.
 If the carrier frequency setting is high, decrease the Pr. 72 PWM frequency selection setting.
Note that motor noise increases. Selecting Pr. 240 Soft-PWM operation selection makes the sound inoffensive.
To ensure that the motor is protected against line-to-line leakage currents, it is recommended to use a temperature
sensor to directly detect motor temperature.
Installation and selection of moulded case circuit breaker
Install a moulded case circuit breaker (MCCB) on the power receiving side to protect the wiring of the inverter input side.
Select the MCCB according to the inverter input side power factor (which depends on the power supply voltage, output
frequency and load). Especially for a completely electromagnetic MCCB, one of a slightly large capacity must be selected
since its operation characteristic varies with harmonic currents. (Check it in the data of the corresponding breaker.) As an
earth leakage current breaker, use the Mitsubishi earth leakage current breaker designed for harmonics and surge
suppression.
Leakage Current (mA) *
Wiring length 50m
Wiring length 100m
620
680
740
800
880
980
1070
*The leakage current of the 200V class is about a half.
MCCB
MC
Inverter
Line-to-line leakage currents path
EMC and leakage currents
Motor: SF-JR 4P
Carrier frequency: 14.5kHz
Used wire: 2mm
1000
Cabtyre cable
1060
1120
1180
1260
1360
1450
Thermal relay
Motor
M
Line-to-line static
capacitances
2
, 4 cores
3
43

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