Which of the listed devices is primarily used for voltage regulation?

The voltage regulator is specifically designed for the purpose of maintaining a constant voltage level in an electrical system. Its primary function is to ensure that the voltage delivered to electrical devices remains stable despite fluctuations in the supply voltage, which can occur due to varying load conditions or changes in the input supply. By providing this regulation, the voltage regulator helps protect sensitive electronic equipment from damage that can result from voltage spikes or drops.

In contrast, a circuit breaker is primarily a safety device that interrupts the current flow during overload or short circuit conditions to prevent damage to the electrical system. A surge protector safeguards electrical devices from voltage spikes, transient voltage events, and lightning strikes but does not actively regulate voltage levels. The transfer switch is used to switch between different power sources, such as from the mains to a generator during a power outage, and does not serve to regulate voltage itself.

Thus, the voltage regulator stands out as the device dedicated to the task of voltage regulation, ensuring stable electrical supply for connected devices.