Difference Between Relay and Circuit Breaker

Main Differences between Circuit Breaker and Relay

A Relay is a switch used as sensing and controlling device which makes and closes the contacts electronically or electromechanically. Relay is also used as a protective device which sense the fault signal and sends to the circuit breaker which make decision to make or break the circuit based on the provided information by the relay. the energized coil as moving part (also known as armature) is connected to the relay contacts while the static coil produces the require electromagnetic field for armature to make or close the contacts for circuit protection.

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A Circuit Breaker is a controlling and protective device which makes and breaks the circuit manually or automatically in case of normal and fault conditions like short circuit and over-current etc. Inside circuit breaker, the relay sense the fault or specified amount of current and sends the signal to the electromechanical switch which open the contacts and protect the circuit in case of excessive current like overload and short-circuit conditions.

There may be a Relay in a Circuit Breaker, but Relay can’t be a Circuit Breaker.

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Differences between Circuit Breaker and Relay

Characteristics	Circuit Breaker	Relay
Symbol
Construction	Circuit Breaker is the combination of internal electromechanical switch and relay mechanism which interrupts the circuit in case of short circuit or overload.	The coil inside a Relay creates electromagnetic field while the solenoid as moving part known as armature opens and closes the contacts when coil is energized.
Function	Circuit Breaker provides interruption only. Faults detection is performed by relay inside circuit breaker.	Relay is a switching device that opens and closes the contacts electronically or electromechanically.
Working Principle	Circuit Breaker automatically breaks the connected circuit when receives an error signal sensed by a relay inside CB.	Relay act as a switching and sensing device and sends the fault signal occurred on power system to the circuit breaker.
Operation	Circuit Breaker makes or breaks the circuit contacts when needed.	Relay only sense the error signal and send it to the circuit breaker.
Types	MCB (Miniature Circuit Breaker), ACB (Air Blast), VCB (Vacuum), SF6 etc.	SPST, SPDT, DPST, DPDT, EMR, SSR, Electromechanical, REED and Hybrid Relay etc.
Type of Device	Circuit breaker is a switching device act as circuit disconnection or isolation.	Relay is a sensing and controlling device act as a switch when needed.
Voltage Level	Circuit Breaker operated on low as well as high power and voltage level and acts automatic on load devices.	Relay operates on low power and voltage input signal with guaranteed isolation when needed for operation.
Controlling the Circuit	Circuit Breaker used to control one per circuit same like a switch.	Relay is used to select or control one among number of circuits.
Used as an Amplifier	Circuit Breaker can’t be used as an Amplifier. I.e. It only receives signal from a relay and make decision based on it.	Relay act as an Amplifier. I.e. it turns one signal into many signals e.g. turn a low-voltage signal into a high voltage signal, or vice-versa.
Applications	Circuit Breaker are used in Low and High currents devices. Home electrical wiring. Industrial equipment and applications. Electrical Machines. power plants, & electricity sharing system (GND).	Relays are used in: Isolating a low voltage circuit from high voltage circuit. Controlling multiple circuits. Microprocessor to o control a heavy electrical load. Automatic change over. Overload relays for motor protection.

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Different Characteristic of Relay & Circuit Breaker

• A Relay can be Directional and Non-Directional, whereas Circuit Breaker is Non-Directional only.
• A Relay only provides signals to the circuit breaker in case of fault conditions while circuit breaker act as automatic circuit making or breaking device based on the information provided by relay signals.
• Relay only sense the error and inform the circuit breaker i.e. it won’t break the contacts. Circuit breaker has both abilities of making and breaking the circuit automatically, manually or by remote control.
• A Relay is a switch acting as a sensing device whereas, circuit breaker is is used for disconnection and isolation of the circuit.
• Relay can be used as amplifier in case of discrete signals i.e. it converts one signal into many, amplify a low voltage signal into a high voltage signal and vice versa. Circuit breaker can’t be used as amplifier. 
• A relay operates on low power and voltage input signals whereas, circuit breakers can be used for low as well high power circuit as its operation is automatic on load devices.
• Relays are controlling devices whereas Circuit Breakers are switching devices.
• A Relay can divert signals between two different electric circuits, whereas circuit breaker can only stop or flow the current in the circuit.
• A Relay won’t be able to prevent the arc. There may be a mechanism to detect the formation of arc and prevent it.
• Finally, a relay may be included in a Circuit breaker, but circuit breaker is not included in the relay.

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