Difference between Circuit Breaker and Isolator / Disconnector

Electrical Technology

Main Differences between Isolator / Disconnector and Circuit Breaker

Table of Contents

Isolator and Disconnetor

As the name suggests, An Isolator or Disconnector is an isolating or disconnecting switch which disconnects or isolate the whole or a specific part of the circuit. It is used where we need to disconnect a portion of the circuit in case of faults from the main power supply for maintenance purposes. Isolator blocks the DC current and allow the AC current to flow through it (same like a capacitor). HV and MV Switch Disconnectors and Isolators are used in high voltage equipment such as transformer, substation etc. Switch Disconnectors are used in MV installation nowadays. HV/MV Switch Disconnectors And Isolators are used where power installations exceeding 1 kV AC (IEC-61936-1).

Keep in mind that isolator or disconnector should not open when the current is flowing through it.
There may a physical and construction difference between Switch Disconnectors, Load Switches, Disconnectors as Isolating Switches but the function is almost same.

Circuit Breaker

A Circuit Breaker is a protective device used to control the flow of current same like a fuse. It break the circuit in case of fault conditions like short circuit and overload. It also capable to operate automatically, manually or by remote control in normal and faulty conditions. A relay inside the circuit breaker sense the errors signal and sends to the mechanical switch which make and close the contacts.

Related Post: Main Difference between Fuse and Circuit Breaker

Differences between Circuit Breaker and Isolator / Disconnector

The following table shows the main differences between Isolators, Disconnectors and Circuit Breakers.

Characteristics	Circuit Breaker	Isolator / Disconnector
Symbol
Construction	Circuit Breaker consists of electromechanical switch and a relay in a single box.	Isolators and Disconnectors are types of simple mechanical switch.
Working	Circuit Breaker is operated Automatically and Manually.	Isolator and Disconnector are operated Manually.
Type of Device	Circuit Breaker is an Electromechanical or electronic device and relay mechanism.	Isolator is a Mechanical Device act as Switch and provides isolation functions.
Function and Operation	Circuit Breaker is a protection device (such as MCB, ACB, SF6, OCB etc) which disconnects the circuit 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.
Types	MCB (Miniature), ACB (Air Blast), OCB (Oil), SF6 etc.	Pantograph ,Knee, Double Break, Center Break, Earthing etc.
ON-Load Operation	Circuit Brekaer is an ON-Load and OFF-Load Device i.e. it operates when the power supply in ON or OFF.	Isolator is an OFF-Load Device i.e. Disconnector can be operated when the power supply is totally OFF.
Withstand Capacity	At ON-Load Conditions, Circuit breaker has the high withstand Capacity.	Isolators have low withstand Capacity as compared to circuit breakers.
Thermal Capability	High	Low
Contacts	It has Main as well as Arcing Contacts.	It has Main and Moving Arms / Blades.
Power Routes	Circuit Breakers can be used to re-route the power Supply.	Disconnector can be used to re-route the power supply.
Trap Charges	It can’t remove the trap charges.	It can remove the trap charges.
Insulation	In CB, Air, Oil, Vacuum or SF6 gas are used as insulation medium.	Isolators don’t require insulation or insulation medium.
Over-voltage During Switching	In Circuit Breakers, there is a chance of rise in overvoltage during switching operation.	In Isolator, there is no overvoltage rise during switching as it is an OFF-Load device.
Earth Switch	Earth Switches are not included in the 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 / Disconector should not be opened when the current is flowing through it. Current flow should be disconnected by Turning off the circuit breaker before.

Related Post: Difference Between MCB, MCCB, ELCB & RCB, RCD or RCCB Circuit Breakers

Different Characteristic of Isolator, Switch Disconnector and Circuit Breaker

Characteristics of Switch Disconnectors

Rated voltage: 2 kV – 36 kV
Rated current: 400 A – 1,250 A
Rated short-time withstand current (3 s): 5 kA – 25 kA

Characteristics of Isolator

Rated voltage
MV: 2 kV – 36 kV
HV:5 kV – 800 kV
Rated current
MV: 400 A – 1,250 A
HV:2,000 A – 5,000 A
Rated short-time withstand current (3 s)
MV: 5 kA – 25 kA
HV:50 kA – 80 kA

Characteristic of Circuit Breaker

Rated Current 10k A and above.
Electromagnetic Circuit breaker must trip in case of over current.
Thermal circuit breaker must trip in case of continues overload.
Mechanical Circuit Breaker must open and close the circuit like a switch.
A Circuit breaker must prevent the re-connection of the circuit in case of existing short circuit current in the circuit.
A Circuit breaker must reconnect the load circuit to the power supply automatically or manually in case of no faults currents i.e. short circuit and overload.