FN3-12 Indoor High-Voltage Load Break Switch Thomas Electric

Product Overview

The FN3-12 and FN3-12R/S series are indoor high-voltage load break switches designed for 50 Hz AC systems operating at 6 kV or 12 kV. They provide reliable switching of load currents and support protection applications when used with compatible high-voltage fuses. Engineered for frequent operation with minimal maintenance, these switches integrate seamlessly into medium-voltage indoor switchgear panels and can be equipped with CS2 or CS3 manual operating mechanisms for enhanced safety and control.

Product Display

FN3-12 Indoor High-Voltage Load Break Switch - poster_display

Model Designation

FN3-12 Indoor High-Voltage Load Break Switch - model

Model format: FN3-12 R(S)

F: load break switch
N: indoor application
3: design sequence number
12: rated voltage, kV
R: with load breaking capability
S: with integrated earth (grounding) switch

Service Conditions

Ambient temperature: standard service conditions apply
Altitude: 1000 m or less standard; consult the technical team for higher altitudes
Humidity: non-condensing, per IEC 62271 practice
Special requirements: custom configurations available upon request

Construction

The switch incorporates an RN3-type arc-extinguishing vacuum interrupter for reliable load current interruption. Terminal markings include P1/P2 for power input and output and S1/S2 for fuse connections where applicable.

The frame is arranged for compact indoor mounting with standardised interface dimensions for ease of integration into switchgear panels, and the CS2 or CS3 manual mechanism is linked to the switch shaft at the panel front.

Technical Data

Parameter	Symbol	Value
System frequency	f	50 Hz
Rated voltage	Ue	6 kV / 12 kV
Rated current	In	200 A / 400 A / 630 A
Rated short-time withstand current (3 s)	Isc	20 kA
Rated peak withstand current	Ipk	50 kA
Mechanical life	N	2000 operations or more
Arc-extinguishing medium	—	Vacuum (RN3-type interrupter)
Operating mechanism	—	CS2 or CS3 manual mechanism

Selection note: ensure fuse coordination for fault protection; the switch alone cannot interrupt short-circuit currents. Confirm the rated load-breaking duty separately from the 20 kA three-second and 50 kA peak withstand ratings, because withstand does not equal fault interruption.

Standards

The source page quotes humidity practice per IEC 62271 but no full standard number for the switch. The usual references for indoor high-voltage load break switches are IEC 62271-102 / IEC 60265-1 and GB/T 3804; confirm the applicable edition with the factory when ordering.

Technical note: custom configurations are available upon request for non-standard service conditions.

Installation & Dimensions

Installation Diagram

The FN3-12 series is designed for compact indoor mounting with standardised interface dimensions for ease of integration into switchgear panels. Verify panel cut-out dimensions and clearance requirements before installation, and ensure all circuits are de-energised during mounting and wiring.

Dimension	Value (mm)
Overall height	480
Overall width	260
Overall depth	190
Mounting hole spacing, vertical	320
Mounting hole spacing, horizontal	200
Phase spacing	150

Safety notice: always ensure the circuit is de-energised before installation or maintenance. Do not operate under load without verifying compatibility with the connected fuse’s interrupting rating, and use only manufacturer-specified replacement parts to maintain safety and compliance.

FAQs

No, the switch cannot interrupt short-circuit currents independently. It must be coordinated with back-up fuses for fault protection, so specify the fuse requirements during system design and coordinate fuse voltage, current, minimum breaking current, striker and time-current curve.

Standard models are rated for altitudes up to 1000 metres. For higher elevations, consult the technical team for derating factors and custom configurations; humidity is non-condensing per IEC 62271 practice.

It uses either the CS2 or CS3 manual operating mechanism, selected for the panel access and interlock arrangement. The RN3-type arc-extinguishing interrupter gives a mechanical life of at least 2000 operations, which suits frequent switching duty.

It is designed for 6 kV and 12 kV indoor high-voltage switchgear applications, integrating into medium-voltage indoor switchgear panels for the reliable switching of load currents and for protection applications when used with compatible high-voltage fuses.

The FN3-12 is available in 200 A, 400 A and 630 A rated currents at 50 Hz. Select the frame from the maximum load, the switching frequency and the panel temperature-rise limits, and specify the exact load requirement when ordering.

R marks the version with load breaking capability and S the version with an integrated earth (grounding) switch. Select the required R/S configuration together with the earthing switch and the CS2 or CS3 mechanism, then verify the mechanical interlocks and door-access logic of the panel.

FN3-12 Indoor High-Voltage Load Break Switch