Created by: Glen Zhu | Updated Date: February 21st, 2025
Isolator Switch and Circuit Breaker are two commonly used electrical components for circuit protection. While both are used to disconnect current, they differ in their functions and applications. This article will explain the differences between an Isolator Switch and a Circuit Breaker in detail.
The isolation switch is a mechanical switch used to manually cut off the current. Its main function is to disconnect the circuit or equipment from the power supply to ensure that electrical equipment is in a power-off state during maintenance, inspection, or testing, effectively ensuring the safety of operators.
It should be noted that the isolation switch cannot be operated when there is a load on the circuit; it can only be used when the circuit is powered off or has no current flowing. When the load current is still present, operating the isolation switch may cause arcing.
Arcing can not only damage the isolation switch itself, but also damage the contacts of the isolation switch, causing it to fail and affecting the normal operation of the entire electrical system. Continuous arcing can lead to fires, especially in environments with flammable materials. If operators operate an isolation switch with a load, arcing may cause electric shock or burns to operators, even fatal.
The isolation switch can be divided into AC isolator switch and DC isolator switch according to the type of current it is suitable for.
Conductive Part: This mainly consists of moving and stationary contacts, contact fingers, terminal blocks, etc., and is responsible for conducting current.
Insulating Part: Includes support insulators, operating insulators, etc., which provide insulation between the conductive parts, the ground, and other components, ensuring the safety of electrical equipment and personnel.
Operating Mechanism: There are various operation methods, mainly manual control of the opening and closing actions of the isolation switch.
Base: Used to fix and support other components, ensuring that the isolator switch is securely installed in the designated position.
The working principle of the isolator switch is relatively simple. It mainly relies on manual operating mechanisms to separate or close the moving and stationary contacts, thus achieving isolation or connection of the circuit.
In the open position, a clear air gap is formed between the moving and stationary contacts, reliably isolating the power source and ensuring the safety of maintenance personnel. In the closed position, the moving and stationary contacts are in close contact, allowing current to flow through the circuit.
Circuit Breaker is an automatic electrical switch used to disconnect current when a fault such as overload or short circuit occurs, thereby protecting electrical equipment and circuits from damage. It can quickly disconnect the circuit when the current exceeds the safe range, preventing fires, equipment damage, or other hazardous incidents.
Contact System: This is the executing component of the circuit breaker, responsible for opening and closing the circuit. It includes moving and stationary contacts, usually made of silver alloy or other materials to ensure good conductivity and corrosion resistance.
Arc Extinguishing System: This system is used to extinguish the electrical arc generated when the circuit breaker disconnects the circuit. Common arc-extinguishing methods include oil arc extinction, gas arc extinction, compressed air arc extinction, SF6 arc extinction, and vacuum arc extinction.
Operating Mechanism: This is used to control the opening and closing actions of the circuit breaker. It can be a manual operating mechanism, electromagnetic operating mechanism, spring operating mechanism, pneumatic operating mechanism, or hydraulic operating mechanism.
Tripping Mechanism: This is the protective component of the circuit breaker. When a fault such as overload or short circuit occurs, the tripping mechanism quickly operates, causing the circuit breaker to trip and disconnect the circuit. Common tripping mechanisms include thermal, electromagnetic, and electronic trip units.
Insulating Components: These components ensure the insulation between different parts of the circuit breaker and between the conductive parts and the ground. They are generally made of insulating materials such as ceramics or epoxy resin.
Normal Operation: During normal operation, the contacts of the circuit breaker are in the closed position, allowing current to flow smoothly through the circuit. The operating mechanism remains in the closed position, ensuring the contacts stay tightly connected to maintain the circuit’s conductivity.
Fault Condition: When a fault such as overload or short circuit occurs, the current flowing through the circuit breaker exceeds its rated current. In this case, the tripping mechanism operates based on the magnitude and duration of the fault current, causing the operating mechanism to release, which drives the contacts to quickly separate and disconnect the circuit, thus protecting the circuit and equipment from damage.
Characteristics | Circuit Breaker | Isolator Switch |
Description | Circuit Breaker is an automatic electrical switch used to disconnect current when a fault such as overload or short circuit occurs, thereby protecting electrical equipment and circuits from damage. | Isolator switch is a type of disconnect switch used in electrical circuits to ensure complete separation of the circuit from the main power supply. The isolation switch is a mechanical switch used to manually cut off the current. |
Circuit Symbol |
|
|
Type of Device | Circuit Breaker consists of an electromagnetic switch and a relay in a single box. | Isolator Switch is a type of simple mechanical switch that provides isolation functions. |
Working | Circuit Breaker is operated Automatically. | Isolator Switch is operated Manually. |
Function | The Circuit Breaker trips the entire system in case of overload and short circuit faults. | The isolator switch provides an isolating function. The other apparatus works without any intrusion. |
ON-Load Operation | Circuit Breaker is an-load device i.e. It operates when the power supply is ON or OFF. | Isolator switch is an off-load device i.e. Disconnector can be operated when the power supply is totally OFF. |
Withstand Capability | The circuit breaker has a high withstand capacity at the condition of on-load. | The isolator switch has a low withstand capacity when compared to the circuit breaker. |
Earth switch | Earth Switches are not included in the circuit breakers. | Single or double earth switches can be included in the disconnector. |
Interruption | Circuit Breaker interrupts the normal as well as short circuit currents during faults. | The isolator switch doesn’t interrupt any current. It only isolates the circuit for maintenance purposes. |
Arc Quenching Technique | A circuit breaker is always provided with some arc quenching techniques. | The isolator switch is not built with arc quenching methods. |
Installation | A circuit breaker is installed within the circuit. | The isolator switch is provided on both sides of the circuit breaker. |
Applications | Circuit breakers find their applications in industrial as well as domestic applications. | Isolators are used in industrial applications. |
Expense | More expensive | Less expensive |
1、Equipment maintenance and repair
Scenario: When it is necessary to maintain, inspect or replace electrical equipment (such as transformers, electric motors, distribution cabinets, etc.).
Scenario: In a complex electrical system, isolation switches are used to divide the system into multiple independent parts.
4、Safety isolation
Scenario: In areas where electrical hazards may exist (such as wet environments, flammable and explosive places).
5、Backup power switch
Scenario: In a dual power supply system, the isolation switch is used to switch between the main power supply and the backup power supply.
6、Testing and debugging
Scenario: When electrical equipment is installed or troubleshooting is needed, the circuit needs to be tested or debugged.
7、Emergency power cut-off
Scenario: In the event of electrical fires, equipment failures, or other emergencies.
1、Circuit overload protection
Scenario: When the current in the circuit exceeds the rated value (for example, when connected devices have excessive power).
2、Short circuit protection
Scenario: When a short circuit occurs in the circuit (such as direct contact between wires).
3、Ground fault protection
Scenario: When a circuit experiences a ground fault (such as a wire touching a grounded object).
4、Equipment protection
Scenario: Used to protect important electrical equipment (such as motors, transformers, generators, etc.) from overcurrent or short circuit damage.
5、Distribution system protection
Scenario: In distribution boxes, distribution cabinets or distribution panels.
6、Frequent operation occasions
Scenario: In situations where circuit switching is frequently required (such as lighting control, motor control).
7、Prevent fires
Scenario: In situations where wire aging, loose connections, or equipment malfunctions may cause a fire.
8、Backup power switch
Scenario: In a dual power supply system, circuit breakers are used to switch between main power and backup power.
9、Temporary fault handling
Scenario: When a temporary fault occurs in the circuit (such as momentary overload or short circuit).
No. The purpose of a circuit breaker is to automatically disconnect the circuit in case of overload or short circuit, but it may not always provide a clear or complete disconnection. In some cases, due to internal faults, mechanical issues, or residual currents, the circuit breaker may fail to fully isolate the circuit. This means that even when the circuit breaker is in the “off” position, the circuit may still be energized, or there may be residual voltage present.
Relying on a circuit breaker for isolation during maintenance poses a risk of the circuit not being completely de-energized. This could expose maintenance personnel to electrical hazards. In worst-case scenarios, failure of the circuit breaker to fully disconnect the circuit during operations could result in electric shock, serious injury, or even death.
Therefore, an isolation switch is specifically designed to ensure complete disconnection and isolation of circuits before maintenance work is carried out. An isolation switch can provide a clear and definite disconnection of circuits, ensuring that there is no power supply to them. It guarantees the safety of maintenance personnel by ensuring that electrical systems are completely de-energized before any physical work or inspection takes place.
When cutting off the power supply, the isolation switch is always operated after the circuit breaker, while the circuit breaker must be operated before the isolation switch. When reconnecting the power supply, the isolation switch should be operated before the circuit breaker, and then the circuit breaker is turned on after operating the isolation switch.
1、Increase safety and reliability.
Installing isolation switches on both sides is equivalent to setting up double isolation protection. Even if one of the isolation switches fails or is operated incorrectly, the other isolation switch may still act as a barrier to prevent accidental electrification.
2、Operational flexibility
When replacing or repairing some components of the circuit breaker, it may only be necessary to disconnect the isolating switch on one side of the circuit breaker, while the other side remains connected, in order to use the power from the other side for testing or inspection work, facilitating step-by-step maintenance and testing of the circuit breaker by maintenance personnel and improving maintenance efficiency.
3、Limit the scope of fault impact
When a circuit breaker and connected lines or equipment fail, timely disconnecting the isolation switches on both sides can completely isolate the faulty part from other normally operating parts, preventing the fault from further expanding to the entire power system and avoiding more serious consequences such as widespread power outages.
4、Meet the needs of different wiring methods
In various complex power system wiring methods, such as single busbar segmented wiring, bridge wiring, etc., the isolation switch on both sides of the circuit breaker is an important component to achieve different wiring functions and can meet different power supply requirements and operational characteristics.
5、Optimize system operation.
By operating the isolation switches on both sides of the circuit breaker in different operating conditions of the power system, the operation mode of the system can be adjusted to achieve economic distribution and optimized operation of electricity.
6、Complies with standards
Many electrical safety standards and regulations require the use of isolators to ensure safe operation and maintenance practices. This helps ensure that installations comply with legal and safety requirements.
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
Copyright © 2010-2025 Wenzhou Arrester Electric Co., Ltd. All Rights Reserved. Privacy Policy
