What Is The Difference between Circuit Breaker and Isolator / Disconnector? .Everyone is aware of the importance of electrical safety measures but many of us lack knowledge of the various types of electrical devices available in the market to ensure the safe functioning of electrical equipment. Switchgear is an umbrella term that comprises the most significant set of devices that augment such safety. The two most common names among switchgear, found almost in every electrical power system, are circuit breakers and isolators/disconnectors. These two devices are indispensable for electrical power systems.
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Both the circuit breaker and the isolator are entrusted with the common function of disrupting or isolating connections in electrical circuits in case there is a problem with the electrical system. This close functional association between the two leads many people to confuse the isolator with the circuit breaker and vice versa. In this article, we are going to bust this common misconception by looking at the difference between circuit breakers and isolators. Let’s get to know more about these essential safety devices.
What is a Circuit Breaker?
A circuit breaker is a device that works like a switch to ensure electrical safety. Circuit breakers are installed in series within an electrical circuit such that they are enabled to stop current flow whenever a fault is detected. The principal function of a circuit breaker is to safeguard against short-circuiting and overloading in a circuit. A relay system is used by the circuit breaker to detect such faults in the circuit. Once faults are detected, it automatically stops the flow of current to prevent damage to both the circuit and connected appliances or equipment.
Circuit breakers come with operating options. They can be switched on automatically as well as manually. They are also equipped with an extinguishing system that allows them to function even during on-load conditions. Circuit breakers are typically attached to electrical devices and equipment such as transformers. They are capable of dealing with heavy load currents.
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Characteristics of Circuit Breaker
- Surge protection: Circuit breakers are primarily designed to protect electrical circuits from overcurrent conditions. They automatically disconnect the circuit when an excessive current flows through it, preventing damage to equipment and mitigating the risk of fire.
- Interrupting capacity: Circuit breakers are rated for their ability to interrupt a fault current safely.
- Tripping mechanisms: Circuit breakers employ different tripping mechanisms, including thermal, magnetic, or a combination of both, to sense and respond to overcurrent conditions.
- Resettable: Unlike fuses, circuit breakers are manually or automatically resettable after they trip.
- Application in various voltage systems: Circuit breakers are used in a wide range of voltage levels, from low-voltage residential applications to medium and high voltage in industrial settings and power transmission.
Types of Circuit Breakers
- Miniature Circuit Breakers (MCB): Used in residential and small-scale setups.
- Molded Case Circuit Breakers (MCCB): Ideal for industrial applications.
- Air Circuit Breakers (ACB): Designed for high voltage systems.
- Vacuum Circuit Breakers (VCB): Suitable for medium-voltage systems.
Common Applications
- Power distribution systems
- Industrial machinery
- Electrical panels in homes
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What is an Isolator/ Disconnector?
Isolators are also often called disconnectors. It is a unit of switchgear that can be used to disconnect the entire circuit or even isolate parts of an electrical circuit. Essentially, an isolator or disconnector is a disconnecting switch that can be used only under off-load conditions, i.e., when there is no current flow in the circuit. This is a principal point of difference between a switch isolator and a circuit breaker.
The disconnector usually comes into use when an electrical system is to undergo repair or maintenance. Such an electrical system needs to be isolated to protect the technician as well as equipment. In the manner of a capacitor, an isolator allows the AC components to function while blocking the DC components.
An isolator is installed separately within the electrical circuit to ensure safe maintenance and repair of faulty sections. The most significant aspect of the isolator is that no current should be flowing through it when it is being operated.
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Characteristics of Isolators/Disconnectors
- Isolation function: Isolators are used to physically disconnect a part of the electrical system for maintenance or repair purposes.
- No current interruption: Isolators are not designed to interrupt current under normal operating conditions. Their primary function is to isolate a section of the circuit for maintenance, allowing personnel to work safely.
- Visible open/closed position: Isolators often have a visible open/closed position indicator to provide a clear visual indication of the state of isolation. This helps ensure that workers can easily determine whether a circuit is isolated or energised.
- Manual operation: Isolators are generally manually operated.
- Limited fault current interruption capability: While isolators can handle some fault current, their primary purpose is not to interrupt fault currents. Circuit breakers are responsible for handling fault currents and protecting the system.
Types of Isolators
- Single-Break Isolators: Common in low-voltage applications.
- Double-Break Isolators: Provide extra safety in medium to high voltage setups.
- Pantograph Isolators: Used in substations for vertical disconnection.
Where Isolators Are Used
- Maintenance of electrical equipment
- Load isolation in substations
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Difference between Circuit Breaker and Isolator / Disconnector
The following table highlights the major differences between Circuit Breaker and Isolator / Disconnector
| Basis of Difference | Isolator | Circuit Breaker |
|---|---|---|
| Description | An isolator is a type of disconnecting switch which is used in an electrical circuit to ensure that the circuit is totally isolated from the supply mains. | A circuit breaker is a protective electrical device that works as a switch and is used to stop the flow of electric current through the circuit wherever necessary. |
| Circuit symbol | 
|
|
| Construction | An isolator is a simple mechanical switch. | A circuit breaker consists of an electromechanical switch and a relay system in a single unit. |
| Operation Method | Isolator can only be operated manually. | Circuit breaker can be operated manually as well as automatically. |
| Type of device | Isolator is an off-load device, i.e. it can only be operated when there is no current flowing through the circuit. | Circuit breaker is an on-load device. Hence, it can be operated under power on conditions. |
| Functions | The major function an isolator is to disconnect the faulty part of an electrical system, so that it will be safe to repair. | The function of a circuit breaker is to protect the entire electrical system, if there is a fault. Also, it serves the function of a switch to cut off the supply wherever necessary. |
| Contacts | A typical isolator has main and moving arms. | A typical circuit breaker has main and arcing contacts. |
| Withstand capacity | Isolator has a low withstand capacity to currents. | A circuit breaker has high withstand capacity. |
| Insulation & quenching medium | Isolator does not need insulation or insulation medium. Isolator uses atmospheric air as arc quenching medium. | Circuit breaker requires insulation medium and arc quenching medium such as air, oil, vacuum, SF6 gas, etc. |
| Provide interruption | Isolator provides the interruption in the power supply only during inspection, maintenance or repair. | Circuit breaker interrupts the power flow during normal as well as fault like short-circuit and overload. |
| Removal of trap charges | Isolator can remove the trap charges. | Circuit breaker is incapable of removing the trap charges. |
| Need of relay system | Isolator does not require relay system for the operation. | Circuit breaker uses relay system to detect the errors in the system. |
| Earth switch | Single or double earth switches can be provided in an isolator. | No earth switch can be included in a circuit breaker. |
| Over voltage during switching | There is no rise of overvoltage during switching of an isolator. | There may be rise in overvoltage during switching of a circuit breaker. |
| Breaking capacity | The breaking capacity of isolator is less, as it cannot be used to break load faults. | The breaking capacity of circuit breaker is more, hence it can be used to break the load faults. |
| Safety | The isolator ensures the safety for technicians and switchgears. | Circuit breaker is not very safe, only professional and well trained technicians can operate it safely. |
| Cost | Isolator is less costly. | Circuit breaker is very expensive. |
| Applications | Isolators find applications only in industrial electrical systems to disconnect the circuit during maintenance | Circuit breakers are widely used in domestic, commercial, and industrial electrical systems for normal switching as well protection from fault. |
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When to Use a Circuit Breaker
Circuit breakers are ideal for scenarios requiring automatic response to electrical issues.
- Protects sensitive equipment from damage.
- Essential in high-risk environments like industrial plants.
When to Use an Isolator/Disconnector
Isolators serve best in maintenance situations, allowing workers to operate on circuits safely.
- Used in substations and distribution lines.
- Provides visual confirmation of power disconnection.
Advantages of Circuit Breakers
- Automation: Eliminates manual intervention during faults.
- Efficiency: Offers instantaneous protection.
- Flexibility: Can be reset after tripping.
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Advantages of Isolators/Disconnectors
- Simplicity: Easy to operate and maintain.
- Reliability: Minimal components reduce risk of failure.
- Cost-Effective: Affordable compared to circuit breakers.
Limitations of Circuit Breakers
- Higher initial and maintenance costs.
- Requires technical expertise for installation and troubleshooting.
Limitations of Isolators/Disconnectors
- Does not provide protection against faults.
- Cannot operate under load conditions.
How Circuit Breakers and Isolators Work Together
In most setups, circuit breakers and isolators complement each other.
- Circuit breakers handle automatic protection.
- Isolators provide a secure environment for maintenance.
Example: In substations, isolators disconnect power after a circuit breaker trips to ensure safe inspections.
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FAQs About Circuit Breaker and Isolator / Disconnector
What is the primary difference between circuit breakers and isolators?
Circuit breakers provide automatic fault protection, while isolators are manual switches for maintenance.
Can isolators operate under load conditions?
No, isolators cannot disconnect live circuits safely.
Are circuit breakers suitable for high-voltage systems?
Yes, specific types like ACBs and VCBs are designed for high-voltage applications.
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