What is the primary function of a relay in electrical systems?

The primary function of a relay in electrical systems is to control high voltage appliances with a low voltage signal. A relay is essentially an electrically operated switch that uses a small amount of electrical current to control a much larger current. This is achieved by using an electromagnetic coil that, when energized by a low voltage signal, creates a magnetic field that actuates a mechanical switch, allowing high voltage devices to be turned on or off safely.

This capability allows for greater isolation between the control side and the higher power side of the system, protecting sensitive components that operate at low voltages from the hazards associated with high voltages. This function is particularly valuable in various applications, such as automotive systems, industrial automation, and home appliances, where different voltage levels need to be managed effectively.

The other options refer to functions that are served by different components or systems. While increasing voltage is done through transformers, converting AC to DC requires rectifiers, and monitoring circuit resistance is typically handled by ohmmeters or similar devices.