Electromechanical assemblies are an important part of industrial applications today. In fact, many companies still use contactors and relays, but some people don’t understand the difference between the two devices. Here is important information to help you know where to use contractors and relays in your circuits.
Contactors
A contactor is a switch, used to connect power directly to large equipment like compressors and motors. They are commonly used for switching high current applications. A single phase 240 volt compressor circuit typically uses a contactor to control the compressor.
Contactors are electromechanical assemblies with coils of wire that turn into electromagnets when they receive electric current. The metal contacts are normally open, and a spring mechanism keeps them apart. Each contact connects to a coil of wire, and when the coils receive power, they magnetically attract the contact to form a connection between the line and load terminals. As long as the coil stays magnetized with electricity, the contact remains closed, and power runs to the device. When power to the contactors ceases to flow, it’s no longer magnetic, and a spring forces the contact away from the power terminals, opening the circuit.
A contactor is essentially a switch which opens and closes automatically without the need for manual operation. For example, when a thermostat sends power to a contactor it turns on the compressor of an AC system. Contactors run on control circuit power which is considerably lower than the power they switch.
Relays
Relays are electromechanical assemblies which work on the same principle as contactors. However, relays switch power on and off within lower voltage control circuits. Relays perform important roles like shutting down entire systems when there’s a power overload. They also switch power between control circuit devices. The main difference between contactors and relays is the amount of power they switch.
