How are heavier currents controlled in a thermostat, considering electrical contacts must be small?

In a thermostat, controlling heavier currents is effectively achieved using a relay. Relays are electromechanical devices that function as switches to control a circuit. When a small input signal, typically from the thermostat, activates the relay, it allows a larger current to flow through a different circuit. This operation is essential for thermostats, as they often need to manage high power loads for heating or cooling systems while maintaining small electrical contacts that cannot handle the high current directly.

The relay contains an electromagnet that, when energized, closes the contacts and completes the circuit for the heavier current. This setup protects the delicate components of the thermostat from damage caused by high currents and ensures that the system operates safely and efficiently. Relays thus serve the essential role of acting as an intermediary that effectively bridges low-power control signals with high-power applications.