Electrical Isolator: Types, Working and its Application

What is Isolator

An isolator is a mechanical switch designed to completely disconnect a part of an electrical system from the power source for safety purposes. Its primary function is to isolate electrical circuits for maintenance or repair by ensuring there is no residual voltage or current present in the isolated section. Isolators are often used in high-voltage and low-voltage electrical systems to provide a visible break in the circuit, indicating that it is safe to work on. Isolators are designed in compliance with IEC 60947-3 and performs below functions:

• Switching : ON / OFF
• Isolation

Unlike circuit breakers or fuses, which are used to protect systems from faults such as overloads or short circuits, isolators do not have automatic tripping functions. They are operated manually and used to disconnect or reconnect a circuit under no-load conditions, meaning the current flow should already be interrupted by other protective devices, such as circuit breakers.

What is an isolation?

Isolation refers to the process of completely disconnecting an electrical circuit or equipment from the power supply to ensure safety during maintenance or troubleshooting. It guarantees that no electrical current or voltage is present in the isolated section of the system. Isolation is critical to protect workers from electric shocks and prevent equipment damage.

When isolation occurs:

• All power connections are physically separated.
• Any stored energy, such as capacitive or inductive loads, is discharged.
• There is no possibility of accidental energization of the system, as the isolator provides a visible open gap that confirms the disconnection.

Isolation means complete disconnection of supply from the circuit. Isolator in OFF position must satisfy the conditions required for isolation as per IEC 60947-3.

Working of an Isolator Switch: The “ON/Off” Operation

The working principle of an isolator is Based on dielectric strength. To stop electricity from flowing, there must be a medium between the contacts so that the voltage cannot “punch” through. In LV isolators switches, that medium is usually ambient air.

The No-Load Requirement

The most critical aspect of an isolator’s operation is that it is a “No-Load” device.

1. Current Interruption & Isolation: An isolator is not designed to “break” an active current flowing through conductor. If you open an isolator while high current is flowing through it, the electricity will try bridge the closing gap, and that will create a dangerous arc.
2. The Sequence: To work safely, a Circuit Breaker should trip first to stop the flow of current. Only then the isolator should move to the “Off” position to provide a better safety barrier.
3. Contact Material: LV isolators switches use high-grade copper or brass contacts, or even silver-plated contacts to minimize oxidation and ensure low contact resistance when the isolator is closed.

Functionality of the Isolator in Transmission Lines

While we are talking about LV isolator switches, it is important to understand about their “big brothers” in the transmission sector. In high-voltage grids, isolators are the “visible safety barrier of the Substation.”

• Sectionalizing: They allow grid operators to isolate a specific transformer or a section of a line for repair or maintenance, without shutting down the regional grid.
• Grounding: Many transmission-level isolators are connected with “Earth Switches.” when the isolator is open, the earth switch closes to drain any residual capacitive charge in the line to the ground, that makes it safe for linemen to touch or operate.
• System Flexibility: They allow for the “re-routing” of power through different busbars during peak load times or emergencies.

Applications of Isolators

Isolators are ubiquitous across every vertical of the built environment:

• Industrial Manufacturing: most heavy machine (lathes, CNCs, conveyor belts) must have an isolator switch. This ensures that if any mechanic is at maintenance or replacing, the remote PLC command or any other remote command cannot accidentally start the machine.
• Renewable Energy: In Solar PV systems, DC isolators are mandatory. Because solar panels produce power if there is light, you need a way to “sever” the connection between the panels and the inverter.
• Data Centers: For PDU (Power Distribution Unit) maintenance, isolators allow for the replacement of components without risking an accidental arc-flash in a high-density environment.

Types of isolators.

Classification on basis of Construction

• Single Break Isolator: A single contact arm moves to disconnect from one fixed contact. These are simple and cost-effective isolator used for low & medium voltages (up to 33 kV).
• Double Break Isolator: This type has three post-insulators. The central insulator rotates, causing a long conductive arm to disconnect from two fixed contacts simultaneously. This creates two gaps in the circuit, providing a higher level of safety and reliability for medium to high voltages (33 kV to 132 kV)We can operate this in two ways:

• Manually: Using a simple hand lever and rod at the bottom.
• Motorized: Using a motor for remote or automatic operation.
• Pantograph Isolator: It uses a scissor-like mechanism that moves vertically to connect or disconnect from an overhead line. Because it moves vertically not horizontally, it saves ground space in high-voltage substations (132 kV to 765 kV).
• Vertical Break Isolator: The conductive blade rotates upward into a vertical position to open the circuit. These are commonly used in outdoor substations because they are less affected by outer environment like ice or heavy wind.

Classification by Location in the System

Isolators are also named based

Classification by Number of Poles

• 1-Pole (1P): Disconnects one live wire; commonly used in residential applications
• 3-Pole (3P): Standard for industrial 3-phase systems; it disconnects all three “live” phases.
• 4-Pole (4P): Disconnects three phases as well as the neutral wire, make sures the total isolation from any potential current.

Special Types: MCB Isolators

In modern homes, you might see an MCB Isolator. While a standard MCB (Miniature Circuit Breaker) trips automatically during a fault, an MCB Isolator is a manual operated switch. It looks like a MCB but don’t have the internal “trip” mechanism—it is used solely to on/off power of the entire consumer unit.

Point to remember: Regardless of the type, a standard isolator has no “arc-quenching” ability. It should not be opened while the circuit is under load (carrying current). Always turn off the circuit breaker first.

Utilization Category for an Isolator according to the type of load

Difference Between Isolator and Circuit Breaker

“If we have a circuit breaker, why do we need an isolator?”

The answer lies in the difference of protection and safety.

A Circuit Breaker is a simple device designed to sense transient such as overcurrent or short-circuit faults and execute a high-speed interruption of the current path under load.

An Isolator Switch is a device that provides a mechanical rupture of the conductive path. It is a “passive” safety device that ensures zero-potential across the downstream circuit by maintaining a visible dielectric gap that cannot be bypassed by errors or mechanical welding of contacts

Electrical Isolator for Air Conditioners

One of the most common consumer-facing applications of an LV isolator is the AC Isolator. If you look at an outdoor condenser unit for a commercial or residential HVAC system, you will see a sturdy, weatherproof box mounted nearby.

Why is this specific application so important?

1. Local Control: A technician working on a roof or behind a building cannot see the main electrical panel inside. The AC isolator ensures they have the “Off” switch within arm’s reach.
2. Weatherproofing (IP Ratings): Since AC units are outdoors, these isolators are usually rated IP66, meaning they are dust-tight and protected against powerful jets of water.
3. Motor Isolation: AC compressors are inductive loads that pull high “in-rush” current. A dedicated isolator ensures that the specific high-draw circuit of the compressor is isolated from the more sensitive control electronics of the indoor unit.

Maintenance of Isolators: Preventing the “Frozen” Switch

Because isolators are not operated frequently, people usually ignore them after they are installed. This is dangerous. if an isolator gets stuck, it becomes useless during an emergency.

Maintenance points:

• Mechanical Exercise: Timely switching the isolator on and off (during scheduled downtime) prevents the internal linkages from seizing due to corrosion.
• Thermal Imaging: By using an infrared camera to check for the “hot spots.” If an isolator contact is getting hot while system is running, it indicates high resistance, which is commonly caused by oxidation or loose termination.
• Cleaning Insulators: In industrial environments, dust or salt can accumulate on the housing of isolator. This can cause a “creepage path” where electricity can leak from the surface of the plastic (Housing).
• Terminal Torque: High vibrations from the machinery present nearby the isolator can also loosen the wire connections. regularly torque checks ensure that the cables remain tight at the screw terminals

Conclusion:

The isolator is a high-value, low-cost electrical safety device. While it may be considered as an “extra” component compared to a circuit breaker, it is the component that provides a clear guarantee of safety and isolation

When designing systems, choosing a high-quality isolator with a clear “ON/OFF” indicator. it is not just a technical choice it’s a commitment to operational excellence and worker safety

Frequently Asked Questions