ALL PRODUCTS

FN7-12(LBS+Fuse) Indoor Load Break Switch

FN7-12(LBS+Fuse) Indoor Load Break Switch

FN7-12 load break switch with fuse combination is a three-phase indoor switching device rated at 12kV, designed for transformer and feeder protection in medium voltage distribution networks. This LBS with fuse combination features epoxy resin insulators for high dielectric strength, color-coded phase barriers for clear visual separation, and a synchronized drive shaft for simultaneous three-phase operation. The galvanized steel chassis provides corrosion resistance and stable mounting geometry. Widely deployed in compact substations, industrial distribution panels, and transformer protection applications, this indoor load break switch offers reliable load switching and short-circuit protection in a single integrated assembly.

Overview
Applications
Technical Data
Services
Quality Control
Recommended Products

FN7-12 Indoor Load Break Switch with Fuse Combination - 12kV

FN7-12 is an indoor air-insulated load break switch for 12kV systems, most commonly supplied as a switch-fuse combination for transformer protection. It makes and breaks load current up to 630A and, when combined with high-voltage current-limiting fuses, provides short-circuit protection at a fraction of the cost of a vacuum circuit breaker.

THE SWITCH-FUSE ECONOMIC ARGUMENT
A vacuum circuit breaker interrupts short-circuit current itself, which requires vacuum interrupters, a stored-energy mechanism, a protection relay, CTs and a station battery. For a distribution transformer feeder rated a few hundred kVA, that is a substantial cost to protect a relatively small asset.

A switch-fuse combination splits the duty. The load break switch handles all normal switching - energising and de-energising the transformer, isolating it for maintenance. The fuse handles short-circuit interruption, clearing a fault in under half a cycle and limiting the let-through energy to a fraction of the prospective fault current. No relay, no CTs, no battery. For transformer circuits up to roughly 1250kVA this is the standard and most economical protection scheme worldwide, and it dominates secondary distribution across Africa, the Middle East and CIS.

Current-limiting fuses also interrupt faster than any breaker, which means less damage to the transformer and less stress on upstream equipment.

STRIKER PIN AND THREE-PHASE TRIPPING
A critical safety feature of the combination is the fuse striker pin. When any one fuse operates, its striker pin mechanically trips the load break switch, opening all three phases. Without this, a single-phase fuse operation would leave the transformer running on two phases - a condition that destroys motors and overheats the transformer winding. Any switch-fuse unit specified without striker-pin tripping is incomplete.

THREE-POSITION OPERATION
FN7-12 provides Closed, Open and Earthed positions from a single interlocked mechanism, giving a visible positive earth before maintenance with no separate earthing device. Mechanical interlocking prevents earthing a live circuit and prevents opening the compartment before earthing.

AIR INSULATION
FN7-12 is air-insulated with no SF6, avoiding F-Gas reporting, leak checking and end-of-life gas recovery obligations - increasingly relevant in EU and Eastern European procurement. It requires a clean, dry indoor environment; in dusty, humid or coastal locations a sealed SF6 unit is the more durable choice.

MARKET FIT
Serves 11kV Middle East and African networks and 10kV Russian, CIS and Eastern European networks, at 50Hz or 60Hz.

Typical Applications

PRIMARY APPLICATIONS
- Distribution transformer primary protection using the switch-fuse combination - the dominant application, typically for transformers from 50kVA to 1250kVA.
- Ring main unit transformer feeder cells in HXGN and compact substation cabinets.
- Compact and packaged substation switching for residential, commercial and light industrial developments.
- Motor circuit switching and isolation on smaller MV motors.
- Capacitor bank switching and isolation.
- Busbar and feeder isolation for maintenance in secondary distribution panels.
- Rural and peri-urban electrification schemes across Africa where cost per connection governs.
- Building services substations in hotels, malls, hospitals and office developments.

WHEN SWITCH-FUSE IS THE RIGHT CHOICE
Specify a switch-fuse combination where the protected load is a distribution transformer up to roughly 1250kVA, the circuit does not require adjustable protection settings, and there is no station battery or relay scheme. It is faster, cheaper and simpler than a breaker.

Specify a vacuum circuit breaker instead where the feeder requires adjustable and coordinated protection, needs auto-reclosing, switches frequently, or feeds a load above the practical fuse range. Note also that a fuse is a consumable: after operating it must be replaced, so a stock of correctly rated fuses must be held on site.

REGIONAL FIT
- Africa: very high volume in electrification and housing schemes on 11kV networks - the cost advantage over breaker protection is decisive at scale.
- Middle East: 11kV secondary distribution and compact substations. Indoor, clean-environment installations only.
- Russia and CIS: 10kV secondary distribution, GOST R certified, GOST 15150 climatic versions available.
- Eastern Europe: 10kV distribution, with air insulation avoiding F-Gas obligations.

NOT SUITABLE FOR
Circuits requiring adjustable protection coordination or auto-reclosing. Frequent switching duty beyond the rated mechanical life. Dusty, humid or coastal environments - specify a sealed SF6 unit. Systems above 12kV.

Technical Data

TECHNICAL DATA - FN7-12 Load Break Switch and Switch-Fuse Combination

Category	Item	Specification
Compliance	Standards	IEC 62271-103, IEC 62271-105 (switch-fuse), IEC 60282-1 (fuses)
Electrical Ratings	Rated voltage	12 kV
	Rated frequency	50 Hz / 60 Hz
	Power-frequency withstand (1 min)	42 kV to earth / 48 kV across isolating distance
	Lightning impulse withstand (BIL)	75 kV peak / 85 kV across isolating distance
	Rated normal current	630 A
	Rated load breaking current	630 A
	Short-circuit making current	50 kA peak
	Short-time withstand current	20 kA for 4 s
	Cable-charging breaking current	10 A
	Transformer no-load breaking current	6.3 A
Switch-Fuse Combination	Breaking capacity with fuse	Up to 31.5 kA
	Fuse type	HV current-limiting fuse (IEC 60282-1)
	Fuse rating range	6.3 A – 125 A (depending on transformer size)
	Striker pin tripping	Standard — any single fuse operation trips all three phases
	Fuse carrier	Draw-out type for safe replacement
Switch Function	Positions	Closed / Open / Earthed
	Earthing switch making capacity	50 kA peak
	Interlocking	Mechanical — prevents earthing live circuit & door opening before earthing
	Operation	Manual lever standard; motorised AC/DC 110 V or 220 V optional
	Auxiliary switch	2NO+2NC standard, expandable
Endurance	Mechanical life	≥2,000 operations
	Load breaking at rated current	≥100 operations
	Earthing switch	10 making operations at rated making current
Construction	Insulation medium	Air
	Insulating parts	Cycloaliphatic epoxy resin
	Contact material	Copper alloy, silver plated
	Mounting	Panel-mounted, vertical or horizontal
	Weight (approx.)	60–90 kg depending on configuration
Service Conditions	Ambient temperature	−25 °C to +55 °C
	Altitude	≤1000 m standard; ≤2000 m on request
	Relative humidity	Daily average ≤95%, indoor clean environment

Services

PRE-SALES SELECTION
- Application review against your duty: rated current, breaking capacity, operating sequence, and expected switching frequency.
- Retrofit and replacement sizing. Send us the existing unit's model, pole-centre distance and mounting dimensions and we will confirm interchangeability before you order.
- Grid verification: 12kV class for 10kV (Russia/CIS) and 11kV (Middle East/Africa) networks; 24kV for 20kV and 22kV; 40.5kV for 35kV. Saudi Arabian supply verified at 60Hz.
- Coil, motor and auxiliary-contact configuration specified to your control voltage (AC/DC 110V or 220V) and SCADA interface requirement.
- Low-temperature variants with cold-rated grease and anti-condensation heating for CIS winter service.

MARKET ACCESS AND DOCUMENTATION
- Type-test reports to IEC 62271-100 / IEC 62271-102 / IEC 62271-103 as applicable, issued with the shipment.
- Third-party certification (KEMA, ASTA, CESI, TUV) available where tender documents require witnessed evidence rather than a manufacturer's report.
- Certification support for SASO SABER, SONCAP, KEBS PVoC, ICIGI and GOST R submissions, including HS-code classification (Nigeria has required 10-digit HS codes since March 2025).

TESTING AND DELIVERY
- 100% routine testing before dispatch: power-frequency withstand, contact resistance, mechanical characteristic curve, timing test, and auxiliary circuit verification.
- Individual test report supplied per serial number.
- Export packing with desiccant and moisture barrier; palletised for consolidated shipment.
- Documentation: routine test report, type-test certificate, dimensional drawing, wiring schematic, O&M manual, spare parts list.

AFTER-SALES
- Installation and commissioning guidance, remote support or engineer dispatch.
- Maintenance training covering mechanism inspection, contact wear measurement and vacuum interrupter integrity testing.
- Wear parts (coils, contacts, mechanism components) held in stock for rapid replacement.
- Technical response within 24 hours; multilingual manuals in English, Russian, French and Arabic.
- Warranty: 18 months from delivery or 12 months from commissioning, whichever expires first.

Quality Control

TYPE TESTING
- Type tested to the applicable IEC standard - IEC 62271-100 for circuit breakers, IEC 62271-102 for earthing switches and disconnectors, IEC 62271-103 for load break switches.
- Verified for rated short-circuit breaking and making capacity, short-time withstand current, power-frequency and lightning impulse withstand, temperature rise, and mechanical endurance across the full rated operating sequence.
- Third-party certification from KEMA, ASTA, CESI or TUV available where the tender requires witnessed evidence.

VACUUM INTERRUPTER CONTROL (where applicable)
- Every interrupter is vacuum-integrity tested before assembly; vacuum degradation is the dominant failure mode in a VCB and is not visible externally once installed.
- Contact stroke, over-travel and contact wear allowance measured and recorded per pole.
- Interrupters sourced only from qualified manufacturers with batch traceability.

IN-PROCESS INSPECTION
- Insulating components partial-discharge tested before assembly.
- Mechanism spring force and charging characteristic verified against specification.
- Pole-centre distance and mounting interface dimensions checked against drawing - critical for retrofit interchangeability.
- Plating thickness on current-carrying contacts verified per batch.

ROUTINE TESTING - 100%, NO SAMPLING
- Power-frequency withstand voltage across the open contacts and to earth.
- Main circuit contact resistance measurement.
- Mechanical characteristic curve: closing time, opening time, contact bounce, and three-phase simultaneity.
- Operating mechanism function at minimum, rated and maximum control voltage - a unit that only operates at nominal voltage will fail during a real disturbance when station battery voltage sags.
- Auxiliary switch continuity and position signalling verification.
- Serialised routine test report issued with every unit.

TRACEABILITY AND SYSTEM
- ISO 9001 quality management system.
- Serial number traceability to vacuum interrupter batch, mechanism batch and insulation component batch.
- Test records retained for the warranty period and available on request.

ENVIRONMENTAL QUALIFICATION
Where the destination environment exceeds IEC reference conditions we qualify against it: elevated-ambient temperature-rise verification for Gulf service, salt-spray testing for coastal sites, and low-temperature operation verification with cold-rated lubricant for GOST 15150 climatic versions.