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Inrush current


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I have a 110vdc to 380vac rotary inverter. At startup the inrush current is 250A which drop to below 50A within 1,5 seconds. the normal running current is 20A. This rotary inverter is only used in emmergencies in case of mains power failure. I rate the wire size at 4 or 6mm2 (for the running current) and the circuit breaker at either 32A or 40A double pole "D" curve. Is this sufficient to accommodate the high inrush current? Will appreciate your input. Thx.
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Hello pieterd1


The correct cable sizing is very much dependent on your local codes and rules.

As a minimum, the cable should be rated above the rated current of the motor (not the current that the motor actually runs at) The start current is very short and so will not cause the cable to fail, but voltage drop cold be significant. This is covered by rules of maximum voltage drop in some regions.


For the best circuit breaker selection, I wold recommend that you talk to the corcuit breaker supplier, that way, if it causes problems, you have someone to go back to. Plus, they are in the best position to give advise (or should be) as they should have all the relevent documentation.


Best regards,

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