Difference between Relay and Circuit Breaker

Relay is a protective device which senses the faulty conditions in a power system line and initiates the operation of circuit breaker to isolate the faulty part from the rest of the healthy power system. That means a relay senses a condition (voltage, flow, amperage, pressure, level, etc.) and allows component actuations (circuit breaker operation, pump start, valve open/close etc.) to occur Examples of relays are Over Current relay, Directional relay, etc.

A circuit breaker is a device for the limiting of current supplied to a circuit.  Circuit Breaker is a device which can

• Make or break circuit under normal conditions either manually or through remote control.
• Break circuit automatically under faulty conditions.
• Make or break circuit under faulty conditions either manually or through remote control.

Some types of circuit breakers are Air blast circuit breakers, Vaccum Circuit Breakers, SF6 Circuit Breakers etc. You can notice the circuit breakers near to the transformers. Next time, when you will see a transformer search for the circuit breaker. Mostly it will be SF6 Circuit Breakers.

What is the difference between Relay and Circuit Breaker?
• The relay is used for controlling a circuit with isolation between control circuit and the controlled circuit. Circuit breaker is used for disconnecting or isolating a circuit from the power source or a higher level circuit.
• The relay operates on a low power voltage input while circuit breakers are automatic on-load devices.
• Circuit breakers are used one per circuit while relays can be used to control/select one among many connected to it.
• A relay may be included in a circuit breaker, but not the other way around.
• A relay can also be considered as an electrical amplifier for discrete signals.