A switching relay can be used to control which of the following?

A switching relay is designed to control the operation of devices by electrically switching them on and off. It can be effectively used in systems that involve both low voltage and line voltage operations. The primary function of a switching relay is to allow a low voltage signal to control a higher voltage circuit, which can include line voltage devices.

When a low voltage signal is applied to the relay, it activates the electromagnetic coil within the relay, causing the contacts to close and allowing electrical current to flow to the line voltage devices. This means that it is capable of integrating low voltage control systems with line voltage loads, making it a versatile component in HVAC and other electrical systems.

This capability to control both low and high voltage allows technicians to use switching relays in a variety of applications, such as managing heating systems, where a thermostat (low voltage) activates a heater (line voltage). The versatility of using a low voltage device to control line voltage equipment is crucial for safety, efficiency, and meeting regulatory standards in installations.

Thus, the correct choice acknowledges this important function of switching relays, distinguishing them from options that limit their application to only one type of device.