Inrush Current

Definition - What does Inrush Current mean?

Inrush Current, also known as Input Surge Current or Switch on Surge, is a large and instantaneous current which exceeds the steady state current value when electrical equipment is switched on. Electric motors, pumps and transformers undergo the Inrush Current immediately they are switched on. The equipment draw several times more current from their full load current when they are first energized.

Petropedia explains Inrush Current

There are many factors due to which an Inrush Current occurs in electrical equipment. They are:

  • The decoupling capacitors or the large capacity smooth capacitors need to be charged first whenever the machine is switched on, which is one of the necessities of powering up the equipment.
  • Whenever a machine is switched on, the filaments and the other parts have low resistance and since the current is indirectly proportional to resistance, higher current is flown through low resistance filament and other parts of machine.

The figure below shows the waveform of a current through an electrical machine when it is just switched on.

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