No-load current

The no-load current is the electrical current that flows in an electrical device, such as a transformer, when it is connected to the rated voltage but no load is being operated.

Even without a connected load, an open-circuit current is required as it is needed to magnetize the iron core. It is made up of a predominantly inductive reactive current component and a small active current component that covers the iron losses.

The power consumed by the no-load current is largely converted in the form of heat losses in the core. From an energy point of view, it therefore makes sense to keep idle losses as low as possible and to disconnect electrical appliances from the mains when they are not in use.

The no-load current is an important parameter for assessing the losses and magnetic properties of a transformer in an unloaded state.