Difference between Isolator and Circuit Breaker

Isolators and Circuit Breakers both are electrical devices used to isolate a section of power system. But what are the differences between them? In this video we are gonna make clear the differences between Isolators and Circuit Breakers which are to be explained considering factors such as type of device and their action, operation of both appliances, their functions, withstand capability and applications, etc.

Difference between isolator and circuit breaker

Before getting down to the point, let’s first figure out the definitions of disconnector (or isolator) and circuit breaker.

Isolator

Isolator is a manually operated mechanical switch that isolates electrical equipment when it needs to be repaired or inspected as part of a regular maintenance schedule for safety reasons. It is used to ensure that the whole or a specific part of the circuit is completely de-energized for service or maintenance. It is also called disconnector or disconnecting switch.

They are only used for breaking the circuit and are often found in electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Unlike load switches and circuit breakers, isolators lack the mechanism to suppress the electric arcs that happens when the high currents are interrupted electrically. Therefore, isolators are called off-load devices. They will not break and make currents. Instead, they will completely isolate currents. So keep in mind that isolator or disconnector should not open when the current is flowing through it. And they may be paired with an earthing switch to ground the portion that has been isolated from the system for ensuring the safety of equipment and the personnel working on it.

Circuit breaker

Circuit breaker on load device

A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by overcurrent/overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault. A circuit breaker can make, carry, and break the current under standard circuit conditions. Hence it is called as an on load device.

A circuit breaker can be used as a protective device that can control the flow of the current just like a fuse. This is a benefit you might not expect from a switch disconnector. It breaks the circuit in case of fault conditions like short circuit and overload. Unlike a switch, a circuit breaker automatically does this and shuts off the power immediately. In this way it works as an automatic service protection device.

MCB (Miniature circuit breaker) has overload and short circuit protection functions. It is also capable of isolation.

Difference between isolator and circuit breaker

Characteristics	Circuit Breaker	Isolator/Disconnector
Type of Device	Circuit Breaker consists of electromechanical switch and a relay in a single box.	Isolators and Disconnectors are types of simple mechanical switch that provides isolation functions.
Working	Circuit Breaker is operated Automatically.	Isolator and Disconnector are operated Manually.
Function	The circuit breaker such as an automatic circuit breaker (ACB) or miniature circuit breaker (MCB) trips the entire system in case of overload and short circuit faults.	Disconnector and Isolator switches provide isolating function i.e. disconnecting the supply from all or a portion of installation e.g. in power plants. The other apparatus works without any intrusion.
ON-Load Operation	Circuit Breaker is an on-load device i.e. it operates when the power supply is ON or OFF.	Isolator is an off-load device i.e. disconnector can be operated when the power supply is totally OFF.
Contacts	It has Main as well as Arcing Contacts.	It has Main and Moving Arms / Blades.
Earth Switch	Earth Switches are not included in the circuit breakers.	Single or Double Earth Switches can be included in Disconnector.
Interruption	Circuit Breaker interrupts the normal as well as short circuit currents during faults.	Isolator doesn’t interrupt any current. It only isolates the circuit for maintenance purpose.
Current Flow Operation	Circuit Breaker can be opened during the flow of current through it. i.e. It can be operated in both cases where the power supply from utility pole is ON or OFF.	Isolator / Disconnector should not be opened when the current is flowing through it. Current flow should be disconnected by turning off the circuit breaker before.
Operation Order	Isolator should be operated after switching off the circuit breaker. Isolator always operates after CB, a CB should operate before isolator.
Installation	The isolator is provided on both sides of the circuit breaker, while a CB is installed within the circuit.
Applications	Isolators are used in industrial applications while CBs find their applications in industrial as well as domestic applications.
Load and fault current	Isolators are never used to make or break load and fault currents while CB is designed to make or break load and fault currents.
Arc quenching technique	The isolator is not built with arc quenching methods, while a circuit breaker is always provided with some arc quenching techniques.

View the video below to know more about difference between isolator and circuit breaker.