Drop-Out Fuse vs. Expulsion Fuse vs. Current-Limiting Fuse: Key Differences You Must Know

When it comes to high-voltage protection, fuses aren’t one-size-fits-all. There are key differences between drop-out fuses, expulsion fuses, and current-limiting fuses — each designed for specific environments, fault levels, and safety needs.

What Is a High-Voltage Drop-Out Fuse?

A drop-out fuse cutout is a high-voltage protective device installed on overhead power lines and pole-mounted transformers. It protects power distribution systems from short circuits, overloads, and equipment failures by interrupting excessive current flow.

These fuses are called “drop-out” because they visibly disconnect （drop down）when they blow, providing a clear indicator of a fault.

How Does a Drop-Out Fuse Work?

In a normal state, current flows through the fuse element. But if a fault current occurs (like a lightning strike or short circuit), the element melts, triggering the fuse holder to swing down and break the circuit.

Most modern drop-out fuses — like the GRL DNHRW12 and DNRW12 series — include an arc-extinguishing tube and spring release mechanism for fast and visible disconnection.

GRL offers a wide range of drop-out fuse options. In addition to the standard models, optional arc-extinguishing hoods are available for faster arc quenching. The insulation material can also be customized, with choices including ceramic or silicone rubber.

Application Scenarios for GRL Drop-Out Fuses

High-voltage drop-out fuses are widely used in:

🏭 Distribution Transformer Protection: Installed on the high-voltage side of transformers.

🌲 Overhead Rural Lines: Isolates faults quickly to prevent power loss to entire sections.

💡 Capacitor Banks: Offers current-limiting protection with visual fault indication.

⚡ Maintenance Switching: Enables safe disconnection during repairs.

Types of High-Voltage Fuses: Understanding Expulsion, Current-Limiting, and Drop-Out Fuses

In medium- and high-voltage distribution systems, choosing the right fuse is critical to ensure safe fault interruption, equipment protection, and service reliability. While the terms drop-out fuse, expulsion fuse, and current-limiting fuse are often used together, they refer to different technologies with distinct structures and applications.

Let’s break them down one by one:

1. Drop-Out Fuse – A Hybrid Design, Often Expulsion-Based

A drop-out fuse refers to the mechanical structure of the fuse, not the arc interruption method. Most drop-out fuses use expulsion techniques, but some advanced types integrate current-limiting elements.

Working Principle:

The fuse is mounted on a hinge or pivot. When the internal fuse element melts, the tube swings open, visibly indicating the blown phase. This makes it easy for line crews to spot and replace the fuse.

Drop-out = mechanical action
Expulsion/Current-limiting = interruption technology

Key Features:

• Clear blown-fuse indication
• Commonly mounted on poles
• Load-break versions can safely interrupt live current

Typical Applications:

• Overhead feeders and lateral lines
• Distribution transformers
• Maintenance switching points in medium-voltage grids

Example – GRL DNHRW12-24/200

This composite-insulated drop-out fuse is rated for 24kV and 200A with load-breaking capability. It integrates an arc extinguishing chamber, making it suitable for rural feeders that require occasional manual load switching.

2. Current-Limiting Fuse – Fast, Silent, and Safe

A current-limiting fuse (CLF) interrupts short-circuit currents without releasing external energy. It limits the peak fault current, providing high-speed protection for sensitive electrical components.

Working Principle:

The fuse contains a precision-melt wire wound inside a ceramic tube filled with quartz sand. When a fault occurs, the element melts and creates a high-resistance arc. The surrounding sand quenches the arc rapidly, limiting the let-through energy and preventing explosion or noise.

Key Features:

• Silent and smokeless operation
• Arc is fully contained
• Reduces mechanical and thermal stress on downstream equipment
• Suitable for indoor or fire-sensitive installations

Typical Applications:

• Indoor switchgear and ring main units (RMUs)
• Transformer primary protection (especially in urban or industrial networks)
• High-rise buildings, metro substations

Example – GRL XRNT1-24/100-40

This 24kV ceramic-body current-limiting fuse can safely break up to 40kA. It’s ideal for compact substations where quiet, reliable fault interruption is essential.

3. Expulsion Fuse – The Traditional Outdoor Protector

An expulsion fuse is a type of high-voltage fuse designed to interrupt faults by expelling hot gases and arc debris through a vent. It is commonly used in outdoor applications like pole-mounted transformers.

Working Principle:

When a fault current flows, the fusible link melts and forms an arc. The arc vaporizes a filler material (typically boric acid), which generates gases to blow out the arc. The tube then “drops out” from the hinge, visibly disconnecting the line.

Key Features:

• Loud operation and visible drop-out
• Expels gas and arc products
• Simple and cost-effective

Typical Applications:

• Rural distribution lines
• Pole-mounted transformer protection

Example – GRL DNRW12 Series

This porcelain-insulated expulsion-type drop-out fuse is ideal for 10–36 kV networks. It’s affordable, rugged, and widely used in overhead rural feeders where cost-effectiveness and visible fault identification are priorities. 

（Because the fuse tube of a drop-out fuse link can fall out, the drop-out fuse is also called an expulsion fuse.）

Why Choose GRL MV Fuses?

1. Over 30 Years of Manufacturing Excellence

GRL Electric boasts over three decades of experience in the electrical protection industry. Our seasoned team of professionals and dedicated R&D department enable us to offer customized solutions tailored to diverse clients

2. Superior Quality Materials and International Standards Compliance

At GRL, we prioritize quality by utilizing premium materials in our manufacturing processes. Our products adhere to international standards, ensuring reliability and safety in various applications.

3. Certified Performance and Reliability

Our Medium Voltage (MV) Drop-Out Fuses have successfully passed TÜV Rheinland’s comprehensive testing, meeting both IEEE and IEC international standards. This certification underscores our commitment to delivering products that perform reliably across diverse power systems.

4. Designed for Challenging Environments

Engineered to handle complex and demanding electrical environments, our Drop-Out fuses come with tailored structural enhancements and insulation choices (porcelain or polymer), providing targeted protection for conditions like high pollution, coastal regions, and areas prone to voltage fluctuations.