What does 'inrush current' refer to?

Inrush current refers to the initial surge of current that occurs when an electrical device is powered on. This phenomenon happens because many electrical devices, especially inductive loads like motors and transformers, require a significant amount of current to start up.

When power is first applied, the device may draw several times its normal operating current for a brief moment. This spike is due to the need to overcome inertia in motors or to charge capacitors in power electronic devices. Understanding inrush current is critical when designing electrical systems, as it can affect circuit breakers, fuses, and overall system stability.

Recognizing this initial surge is important for safe and effective circuit designs, and it informs decisions regarding equipment ratings and protections to prevent potential damage from excessive currents.