What is an Electrical Isolator : Working & Its Applications

The isolator is one type of switching device, and the main function of this is to make sure that a circuit is totally not triggered in order to perform the preservation. These are also recognizable like isolation switches to isolate the circuits. These switches are applicable in industrial, distribution of electrical power, etc. High voltage type isolation switches are utilized in substations for permitting isolation of equipment like transformers, circuit breakers. Usually, the disconnector switch is not proposed for circuit control but it is for isolation. Isolators are activated either automatically or manually. This article discusses an overview of what is an electrical isolator, its types, and its applications.

What is Electrical Isolator?

The isolator can be defined as; it is one type of mechanical switch used to isolate a fraction of the electrical circuit when it is required. Isolator switches are used for opening an electrical circuit in the no-load condition. It is not proposed to be opened while current flows through the line. Generally, these are employed on circuit breaker both the ends thus the circuit breaker repair can be done easily without any risk.

Electrical Isolator
Electrical Isolator

Electrical Isolator is used to separate any type of electrical component from the system while the system is offline/ online. Isolator doesn’t include any kind of system for avoiding arching throughout disconnection. As in an electrical substation, an electrical isolator switch is mainly used for disconnecting a power transformer once it is in a no-load situation otherwise a little load is there. In full load condition, isolators don’t operate.

Working Principle

An electric isolator working principle is extremely easy as it operates in different ways like manually operated, semi-automatic, and fully-automatic. Sometimes, these are used like switches so-known as electrical isolator switches. This switch can be opened or closed depending on the necessity. However, several times, these are arranged in a fixed position permanently to maintain isolation like transformers, in electrical transmission lines, grid stations.

An electrical isolator switch is one kind of device used to isolate a specific circuit by maintaining as well as preventing flowing currents. These switches are used in electrical appliances like kitchen tools, power grids, etc. Isolator switches are available in different types like a single-pole, double-pole, 3-pole, 4-pole, fused, and battery isolator switches.

Operation of Electrical Isolator

When there is no arc quench method is offered in the electrical isolator, it should be worked once there is no possibility of current flow throughout the circuit. So, no live circuit must be open otherwise closed through the isolator process.


A complete live closed-circuit should not be opened through the isolator process & also a live circuit should not be closed as well as completed through the isolator process to keep away from huge arcing among isolator contacts. So, this is the reason isolators should be open once the circuit breaker is open. Similarly, the isolator must be closed once the circuit breaker is before closed.

The operation of an isolator can be done through hand locally & using mechanical mechanism from a remote location. The arrangement of motorized operation is expensive as compared with hand operation; therefore choice must be taken before selecting an electrical isolator for the system which operates manually or mechanically is best for the system.

The isolators which operate manually can be operated by using the system with up to 145 kV whereas, for high voltage systems using 245 kV otherwise 420 kV, motorized isolators are utilized.

Types of Electrical Isolator

The electrical isolators are classified based on the requirement of the system which includes the following.

  • Double Break Type Isolator
  • Single Break Type Isolator
  • Pantograph Type Isolator
Types of Electrical Isolators
Types of Electrical Isolators

Double Break Type Isolator

This type of isolator consists of three loads of post insulators. The middle insulator holds a flat male or tubular contact that can be turned straightly by a spin of the middle post insulator. The rotation of the middle post insulator can be done by a lever method at the bottom of the post insulator, as well as it is related to manual operation (operating handle) or motorized operation motor (using motor) of the isolator via a mechanical knot rod.

Single Break Type Isolators

In this type of isolator, arm contact is separated into two elements. The first arm contact holds male contact, as well as second arm contact, holds female contact. The arm contact shifts because of the post insulator rotation upon which the arm contacts are fixed.

The post insulators’ rotation stacks in reverse to each other which makes to shut the isolator by shutting the arm contact. Post insulators counter-rotation stacks to open the arm contact, as well as an isolator, rotate into an off condition. Generally, the motor-operated isolator is used however an emergency manual operated isolator is also offered.

Pantograph Type Isolator

The pantograph type isolator permits current switchgear installation, and it requires the least space. This type of insulator includes a post insulator as well as an operating insulator.

According to the power system location, the isolator can be classified into three types namely bus side, line side, and transfer bus side isolator.

Power System Location based Isolators
Power System Location based Isolators
  • Bus Side Isolator is a type of Isolator that connects by the major bus.
  • Line Side Isolator stay connected by a feeder inline side.
  • Transfer Bus Side Isolator stay connected by the major bus of a transformer.

Electrical Isolator Operation

The operation of an electrical isolator can be done by the following two operational methods namely opening and closing.

Opening Operation of Electrical Isolator

  • In the beginning, open the major circuit breaker.
  • Then divide the load from a system with an isolator opening
  • Close the earth switch. Earth switch can become an interlock system with an isolator. That’s means when the isolator is open only that time earth switch can be closed.

Closing Operation of Electrical Isolator

  • Detach the earth switch.
  • Shut the isolator.
  • Shut the circuit breaker.

Difference between Electrical Isolator and Circuit Breaker

The main difference between the isolator as well as the circuit breaker is that the isolator detaches the circuit at the OFF-load situation while the circuit breaker detaches the circuit at the ON-load situation.

But these two have a similar principle like disconnection for isolating the parts of the electrical circuit from the system. This cannot function in an on-load situation where there is any fault that occurs in the system then the circuit breaker will trip routinely. The main differences between these two are discussed below.

Type of Device

An isolator is an off-load apparatus whereas a circuit breaker is an ON-load apparatus.


The operation of the isolator is manual whereas the operation of the circuit breaker is automatic.

Device Action

The isolator is one type of mechanical apparatus that works like a switch whereas a circuit breaker is an electronic apparatus made with BJT or MOSFET.


When a fault occurs in a substation, the isolator cuts out a portion of a substation. The other apparatus works without any intrusion.

The circuit breaker is like an MCB or ACB that trips the complete system if there is an error occurs

Withstand Capacity

  • Isolators have a small withstand capacity when contrasted to Circuit Breaker.
  • Circuit breakers have a high withstand capacity at the condition of ON-load.

An insulator is one type of detaching switch which works under the condition of off-loading. It separates the circuit part in which the error takes place from the power supply. Isolators are applicable for high voltage devices like transformers. The main function of the Isolator is, it blocks the DC signals & allows the AC signals to flow.

Circuit Breaker is one kind of protection device which works like a switch. When the fault happens in the system, it opens as well as closes the circuit contact. It separates the circuit automatically when a short circuit or overload takes place.

Earthing Switches

The arrangement of earthing switches can be done on the bottom of the line side isolator. Usually, these switches are broken vertically. Earthing arms are connecting horizontally at off-state throughout switching on the process where these arms turn as well as a move to a vertical place to make contact with earth female contacts which are fixed at the peak of the post insulator stack at its outgoing face.

So, these arms are interlocked by the moving contacts of the main isolator that can be closed simply once the main contacts of the isolator are in an open situation. Likewise, the contacts of the main isolator can be closed simply once the earthing arms are in an open situation.

What is the Role of Isolator in Transmission Line?

Electrical isolators play a key role within a transmission line like insulators isolate the transmission line from the conductor. Here, isolators are mainly useful to eliminate grounding loops like lowering the hazard of accidental lanes for the flow of current towards the ground.

How to Maintain Electrical Isolators?

Electrical isolators suffer from different mechanical problems, so to overcome this, proper maintenance is required. In power systems, isolators are switches where their opened and closed positions are visible clearly. Generally, isolators are operated in offload conditions whereas some isolators operate in on load conditions. There are two essential parts in an isolator like the insulating part as well as conducting part. So some actions need to take for maintaining isolators properly from mechanical issues.

  • We need to clean the insulator body by removing salt cement as well as acid fumes if build-up.
  • If we found any defect, then we have to replace the isolator with a new one. If the defect on an isolator is very small, then we can rub to clean it by using sandpaper. And, contact rods proper arrangement must be checked while maintaining.
  • We must connect the bolts and their connections like power and earth tightly. Before closing the isolators, we need to cross-check whether the male contacts are fitted properly into female contacts or not, otherwise, we need to adjust.
  • We need to check the working of the mechanical interlock by closing the earth switch once the isolator is closed. If the physical operation is not possible then we can use the mechanical operation to rectify it.
  • Frequently, we need to grease the assembly of shaft bearing with mechanical connections of auxiliary switches.
  • We should determine the contact resistance for every contact of every phase. For that, we can employ a ‘Digital Micro Ohm Meter’.
  • Finally, we must verify the electrical interlocking method for every isolator.

Electrical Isolator for Air Conditioner

The cheaper option while installing AC is to connect the aircon unit to the switchboard directly. When doing this connection, still meets production standards.. Isolator switches are arranged on the outdoor units once we set up home AC for two main reasons. Initially, it means you can separate your unit to defend it from strikes in a cloudburst.

Secondly, you can avoid your home security switch from frequently tripping if your AC system has an error. So in this situation, the power supply toward the unit can be disconnected easily with the help of the isolator switch till the electrician comes to repair it.

Electrical Isolator Selection Guide

Electrical isolators operate at no-load conditions, therefore many factors need to be considered while selecting isolators include the following.

  • Voltage level
  • Rated continuous current carrying capability
  • Selection of short duration current capacity
  • Breaker tripping & closing timing
  • Breaker open & close capacity is also significant

Applications of Isolator

The applications of isolators include the following.

  • The applications of Isolators involve high voltage devices such as transformers.
  • These are protected with a locking system on the external or with a lock to stop accidental usage.
  • Isolator in Substation: When a fault occurs in a substation, then the isolator cuts out a portion of a substation.

Thus, this is all about an overview of the electrical isolator. The characteristics of this isolator include it is an offload device, operated manually, De-energize the circuit, entire isolation for secure maintenance, includes a padlock, etc. Here is a question for you what is an isolator in the microwave?