Functions of a Relay

4 Core Functions

1. Automatic Control
A small control signal (from a microcontroller, sensor, or PLC output) is used to energize the relay coil. When the coil is energized, the contacts are activated to automatically switch on a high-power load, eliminating the need to manually operate high-voltage circuits.

Example: When a thermostat detects that the temperature is too high, it activates the relay, which then starts a high-power fan.

2. Electrical Isolation (Separation of Low and High Voltage)
The control side (low-voltage circuit) and the load side (high-voltage circuit) are electrically isolated from each other. The relay transfers the switching action through a magnetic field, protecting the control board and preventing high voltage from entering and damaging low-voltage components.

3. Increased Control Capacity
A low-voltage signal of only a few volts and several tens of milliamps can control high-power equipment through the relay contacts, such as devices operating at 220V/380V and carrying tens of amperes.

4. Multi-Circuit Switching and Interlocking
Some relays have multiple sets of contacts, allowing several circuits to be switched on or off simultaneously. They can also be used for interlocking to prevent two circuits from being energized at the same time, which is commonly used for motor forward/reverse control.