FN18-12 FN18-24 Indoor High Voltage Load Break Switch and Fuse Combination

The FN18-12 and FN18-24 series indoor high voltage load break switches and fuse combinations are medium voltage air insulated switch disconnectors designed for 12kV and 24kV distribution systems.

Equivalent to ABB NAL/NALF type load break switches, the FN18 series combines advanced puffer-type arc extinguishing technology with compact modular construction, providing reliable load switching and transformer protection for switchgear, ring main units (RMU), and compact substations.

Product Features

• Rated voltage: 12kV / 24kV
• Rated current: 400A / 630A / 1250A
• Indoor air insulated structure
• Puffer-type arc extinguishing system
• Fuse-switch combination available
• Optional earthing switch configuration
• Compact modular design
• Reliable load switching performance
• Manual or motorized operating mechanism
• Mechanical and key interlocking supported
• Suitable for metal enclosed switchgear and RMU systems
• Equivalent replacement for ABB NAL/NALF load break switch

Technical Specifications

Working Principle

The FN18 load break switch adopts a compressed-air and gas-generating puffer arc extinguishing chamber. During opening operations under load conditions, the mechanism generates airflow that rapidly cools and extinguishes the arc, ensuring safe interruption of load current while minimizing contact erosion. In fuse combination versions, high voltage current-limiting fuses provide short-circuit protection and automatic tripping functionality.

Main Configurations

FN18 Standard Load Break Switch

• Three-pole load switch
• Suitable for cable and line switching
• Compact switchgear installation

FNR18 Fuse Combination Type

• Integrated high voltage fuse holders
• Transformer and motor protection
• High short-circuit interruption capability

FN18 with Earthing Switch

• Quick-make grounding switch
• Enhanced maintenance safety
• Mechanical interlocking system

Applications

The FN18 indoor load break switch is widely used in:

• Ring Main Units (RMU)
• Medium voltage switchgear
• Compact substations
• Transformer protection systems
• Industrial power distribution
• Utility substations
• Urban distribution networks
• Renewable energy substations
• High-rise building power systems

Product Advantages

Equivalent to ABB NAL/NALF

Compatible design and performance suitable for replacement and OEM switchgear applications.

Reliable Arc Interruption

Puffer-type air insulation technology ensures efficient and stable load switching operations.

Compact Modular Design

Flexible configurations allow integration into various switchgear and RMU systems.

Integrated Protection

Fuse combination type provides reliable overload and short-circuit protection for transformers and cables.

Optional Accessories

• Motor operating mechanism
• Auxiliary contacts
• Fuse trip mechanism
• Grounding switch
• Shunt trip device
• Mechanical door interlock
• Key interlock
• Remote control system

Compliance Standards

• IEC 60265-1
• IEC 62271-103
• IEC 62271-105

Outline Dimensions

FN18 12kV 17.5kV and 24kV load break switch