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Relay vs Circuit Breaker vs Isolator | Difference between Relay, Circuit Breaker and Isolator

This page compares Relay vs Circuit Breaker vs Isolator and mentions difference between Relay, Circuit Breaker and Isolator.

What is Relay?

• The relay is controlled device which opens and closes contacts in order to effect operation of other devices in the same or another electric circuit.
• The relay is used in circuits with lower ampere capacity i.e. Max. 20A.
• They are smaller in size.
• They have at least two NO/NC contacts.
• They are used in control circuits, automation circuits, protection circuits and switching circuits.

Relay vs Circuit Breaker vs Isolator

What is Circuit Breaker?

• It is used to protect electrical circuit from damage as a result of over current due to short circuit.
• It basically interrupts current flow when a fault is detected. It can be reset to normal operation after fault is handled or repaired. Hence circuit breaker can be reused multiple times unlike fuse which can be used only once.
• It is a device which can make or break the circuit under normal conditions either manually or through remote control.
• The main reason for its popularity is that, it can break the circuit automatically under faulty conditions.
• Examples: Air blast circuit breaker, S56 circuit breaker, vaccum circuit breaker etc.

What is Isolator?

• The device used to disconnect part of system for maintenance purpose and repairs is known as Isolator or Isolating Switch.
• It can open the circuit under no load condition only.
• Due to the above characteristic, when two isolators are connected on either sides of a circuit breaker, it must be opened before opening isolators.
• After the maintenance work on circuit breaker is completed, isolators must be closed first and later circuit breaker need to be closed in order to bring system into operation.

Following table mentions difference between Circuit breaker and Isolator.

Specifications Circuit Breaker Isolator
Function Circuit breaker is ON LOAD device. Isolator is OFF LOAD device.
Where used? It is found in power distribution and power generation stations as well as homes. It is found in power generation stations and electrical distribution plants.
Arc Quenching technique Provided Not provided
Location It is connected in circuit. It is connected on both the sides of an area.
Automatic/Manual It is automatic device. It can be operated both automatically or manually.
Maintenance requirement It requires maintenance check after every 10 to 15 years. It requires maintenance check after every 2 to 5 years.
Sequence of use when they are in the same circuit It should always operate before the isolator device. It should always operate after the circuit breaker.

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