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The kW figure in inverter catalogues is an approximate label assuming a typical motor. What actually limits an inverter is the continuous output current it can supply and its short-time overload capacity. Two motors of the same power can have different currents depending on the number of poles and efficiency.
Criteria to consider together:
| Criterion | Why it matters |
|---|---|
| Motor nameplate current | The inverter's continuous output current must cover it; current varies with poles and efficiency. |
| Load type | Fans and centrifugal pumps are light duty; conveyors, crushers and mixers count as heavy duty. |
| Overload class | Normal and heavy duty classes differ in short-time current capacity; a heavy start may need the next size up. |
| Starting and braking | Short ramp, large inertia or frequent start-stop; need for a braking resistor. |
| Ambient | High temperature, altitude and an enclosed panel may require derating the inverter current. |
| Cable length | A long cable causes extra capacitive current and may need a filter. |
For example, the 7.5 kW 132M-4 motor has a rated current of 14.3 A at 400 V; the continuous current of the selected inverter should not be below this. For the currents of other ratings and speeds, the electric motor current table can be used. The final inverter selection is made with the inverter manufacturer's catalogue and the application data.