Outline Table

Load Break Switch: Complete Technical Guide

A Load Break Switch (LBS) is one of the most essential components used in medium-voltage (MV) distribution networks. Its primary function is to switch electrical loads safely while providing visible isolation and reliable operation. Although it cannot break high short-circuit currents like a circuit breaker, an LBS is vital for feeder switching, ring main units, transformers, and distribution automation systems. Because the LBS operates with simplicity and high reliability, it has become a standard piece of equipment in 12kV, 24kV, and 36kV networks across utilities and industries.

The LBS is widely chosen for medium-voltage distribution because it is cost-effective, compact, and easy to operate. More importantly, it offers high safety through visible isolation and mechanical interlocking. These features help utilities reduce operational errors and enhance protection coordination in a distribution grid.

Understanding Load Break Switch Function

The LBS is designed to make, carry, and break normal load currents. However, it is not designed to interrupt fault currents. Instead, it should cooperate with upstream protective devices, such as fuses or vacuum circuit breakers. Therefore, the LBS plays a crucial role in load isolation, feeder switching, and sectionalizing, which are essential operations for system reliability.

Because it is used frequently in MV networks, the LBS must operate smoothly even under varying load conditions. Its arc extinguishing method ensures safe current interruption, while its mechanical linkages ensure visible and reliable position indication.

Application Areas of Load Break Switch

Load break switches are commonly applied in:

• RMU (Ring Main Unit)

• Compact substations

• 12kV / 24kV switchgear

• Distribution transformer protection

• Feeder automation schemes

• Solar and wind power distribution boxes

• Industrial distribution rooms

Because the LBS can safely switch load and isolate feeders, it is widely used in distribution networks requiring high reliability and low maintenance.

Types of Load Break Switches

There are three major types:

1. SF6 Load Break Switch

Uses SF6 gas for insulation and arc quenching.

2. Air Load Break Switch

Uses compressed or natural air as the insulating medium.

3. Vacuum Load Break Switch

Uses a vacuum interrupter for switching but still acts as an LBS.

Each type has different advantages depending on the environment and system requirements.

Internal Structure of a Load Break Switch

A typical LBS includes:

• Fixed contacts

• Moving blade contacts

• Arc extinguishing chamber

• Operating shaft

• Toggle mechanism

• Springs

• Insulating enclosure (air, epoxy, gas)

• Interlocks

• Position indicators

Everything is designed for safe and quick switching with controlled arc extinguishing.

Operating Mechanism

The LBS can be:

• Manually operated using a handle

• Motorized for remote switching

• Spring-assisted to ensure fast operation

The fast “snap action” mechanism ensures that switching speed does not depend on operator strength.

Arc Quenching Principles

Air LBS

Arc stretches and cools in air.

SF6 LBS

Gas provides strong arc cooling and de-ionization.

Vacuum LBS

Contacts separate in a sealed vacuum bottle.

Arc quenching must be reliable, consistent, and safe even under high load.

Electrical and Thermal Ratings

Common ratings include:

• Voltage: 12kV, 24kV, 36kV

• Current: 400A, 630A, 1250A

• Breaking load current: 16A–630A

• Making capacity: 2.5kA–6.3kA

• Peak withstand current: 40–80kA

Thermal design ensures stable performance at maximum load.

Insulation Methods

The LBS insulation can be:

• Air-insulated switchgear (AIS)

• Gas-insulated (SF6)

• Solid insulated

• Hybrid insulated

Each insulation type impacts dimensions, cost, and environmental impact.

IEC and IEEE Standards

Major standards include:

• IEC 62271-103 (Load break switches)

• IEC 62271-100 (Switchgear)

• IEEE C37 series

These standards ensure safety, performance, and interoperability.

Blade Contact Design

Blade contacts are typically silver-plated copper, offering:

• High conductivity

• Low wear

• Good mechanical strength

• Low resistance

The design allows smooth closing and opening.

image of medium-voltage load break switch device

Interlocking Systems

Interlocks prevent:

• Closing onto faults

• Opening under high current (for certain designs)

• Misoperation

• Access to energized compartments

Electrical interlocks can integrate with SCADA.

Visible Isolation

One of the major benefits of an LBS is that the operator can visually confirm whether the switch is:

• OPEN

• CLOSED

• EARTHED

This greatly enhances safety in maintenance operations.

Fault Behavior and Protection Coordination

Since the LBS cannot break fault currents, protection coordination is important:

• Upstream VCB clears faults

• Fuses can protect transformers

• Relays monitor conditions

This coordination ensures safe operation.

Installation Options

The LBS may be installed in:

• Indoor switchgear

• Outdoor pole-mounted boards

• RMUs

• Pad-mounted substations

It must be mounted securely and aligned correctly.

Maintenance Requirements

LBS devices require minimal maintenance:

• Periodic cleaning

• Contact inspection

• Interlock testing

• Mechanism lubrication

• Gas pressure check (SF6 types)

Maintenance interval is typically 2–5 years.

Safety Advantages

• Visible disconnect

• Reliable arc quenching

• Clear indication

• Simple mechanism

• High insulation level

• Suitable for automation

These benefits make the LBS a preferred switching device.

Environmental Impact

SF6-based LBS are being replaced with:

• Air-insulated LBS

• Solid-insulated LBS

• Vacuum-based LBS

This shift aligns with global environmental policies.

Comparison: LBS vs Circuit Breaker

Comparison: LBS vs Disconnector

Disconnector = isolation only
LBS = load switching + isolation

Modern RMU LBS Technology

RMUs often use:

• SF6 LBS

• Solid insulated LBS

• Vacuum LBS

They integrate automation and compact insulation.

Smart LBS Technology

Smart features include:

• Sensors

• Remote operation

• IoT monitoring

• Fault passage indication

• Load monitoring

This supports grid automation and smart city infrastructure.

Future Trends

• SF6-free designs

• High-durability materials

• Integrated vacuum switching

• Smaller, smarter, safer LBS

• Predictive maintenance

Conclusion

The Load Break Switch is a reliable, efficient, and essential component of modern MV networks. It provides safe switching, visible isolation, and long service life while supporting distribution automation and environmental sustainability. Regardless of insulation type, the LBS will continue to play a central role in 12kV–36kV power systems.

FAQs

What is a load break switch?
A device that can switch load current safely and provide visible isolation.

Can an LBS break fault current?
No, it must work with fuses or a circuit breaker.

What voltages are common?
12kV, 24kV, and 36kV.

What types exist?
SF6, air, vacuum, and solid insulated.

Is maintenance required?
Minimal periodic inspection.

Can an LBS be motorized?
Yes, for automation and remote control.