E6582062ï‚‚
2-69 2. Installation and wiring
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â– Influence of leakage current across lines (in case of thermal relays)
The high frequency component of current leaking into electrostatic capacity between inverter output
wires will increase the effective current values and make externally connected thermal relays operate
unnecessarily. When the wires are long (50 m or more) or in case of models with motors of low rated
current (several A (ampere) or less), especially the 480 V class low capacity (4.0 kW or less, 5.5 kW
or less with ND) models, it will be easy for the external thermal relay to activate unnecessarily,
because the ratio of leakage current against the motor rating will increase.
Here are some examples of measures against leakage current across lines.
• Use the electronic thermal of the inverter.
The setting of the electronic thermal is done with <tHrA: Motor overload protection current 1>. For
details, refer to [5. 2. 5].
• Decrease <F300: Carrier frequency>.
However, note that the motor magnetic noise is increased.
For details, refer to [6. 14].
• Install 0.1 to 0.5μF - 1000 V film capacitor to the input/output terminals of each phase in the
thermal relay.
Inverter
Power
supply
Thermal relay
M
A
CT
Leakage current path across wires
Thermal relay
Inverter
M
U/T 1
V/T 2
W/T 3
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