Answer 5—The magnetizing current is the reactive current that flows in the primary of a transformer when the secondary is not loaded. Under these conditions, the primary looks like a relatively pure inductance. The current waveform lags the voltage by 90°.

If a resistive load is placed across the secondary, an in-phase current component is added to the magnetizing current. The wire used in the primary must be sized to handle the vector sum of both currents.

Contributor: David Tweed