What does the term "in-rush" refer to in coil specifications?

The term "in-rush" specifically refers to the momentary surge of voltage that occurs when a coil is initially energized. When current first flows into the coil, there can be a significant spike in voltage as the magnetic field begins to build. This initial in-rush current can be much higher than the normal operating current, which can cause stress on the components if not properly accounted for in the design and operation of the circuit.

Understanding in-rush is critical for applications involving coils, such as relays or solenoids, because it can impact the performance and longevity of the device. It helps engineers to design circuits that can accommodate these brief surges safely and effectively, ensuring that they work properly without damage or failure during startup.

In contrast, the other choices describe different voltage-related concepts: the maximum voltage rating pertains to the highest voltage the component can handle safely, the steady operational voltage refers to the voltage maintained during regular functioning, and the voltage drop across the coil describes the voltage lost as current flows through the coil's resistance.