How does a voltage regulator function?

A voltage regulator is designed to maintain a steady output voltage despite variations in input voltage or load conditions. When we consider the function of a voltage regulator, it plays a crucial role in ensuring that the voltage supplied to electrical devices remains within a specified range, typically at a set value that is close to the line voltage.

The choice that states the regulator maintains voltage at 10% above or below line voltage highlights its primary function, which is to ensure that fluctuations in voltage do not exceed this threshold, providing consistent and reliable voltage to equipment. By doing so, it protects electrical devices from overvoltage or undervoltage conditions that could lead to malfunctions or damage.

The other options address aspects that do not encapsulate the core operation of a voltage regulator. Disconnecting circuits does not describe regulation but rather the action taken under fault conditions. Increasing the current is not an action of a regulator; rather, it is about maintaining voltage levels. Providing isolation from faults is more related to protective devices in electrical systems rather than the specific function of regulating voltage. Thus, the proper understanding of a voltage regulator's purpose aligns with maintaining voltage stability around a given nominal level.