12kV 400A Indoor Load Break Switch | STELLAR Medium Voltage Switchgear

FN3 12kV 400A Indoor High-Voltage Load Break Switch

Product Description

STELLAR indoor high-voltage load break switch is a three-phase device rated for 12kV and 400A. It runs on 50Hz or 60Hz industrial distribution networks and uses compressed-air arc quenching to break normal load currents safely.

The conductive path is built from high-conductivity copper with silver-plated contact surfaces. When paired with a high-voltage current-limiting fuse, the combination unit protects distribution transformers against overload and short-circuit faults. A visible isolation gap opens when the switch is in the off position, meeting safety requirements for maintenance access.

The standard manual operating mechanism uses a direct-drive handle with mechanical interlocks. The switch cannot be closed unless the fuse compartment is properly seated, and the fuse door cannot be opened while the main circuit is energised. This makes it suitable for substations, industrial plants and commercial distribution rooms where space is limited and operator safety is critical.

Typical installations include 10kV/12kV indoor transformer substations, cable distribution boxes and factory switchgear lines. The unit is type-tested to IEC 60265 and GB 3804 for insulation, temperature rise, short-time withstand and mechanical endurance.

Technial Parameters

TECHNICAL PARAMETERS	UNITS	VALUE
Rated voltage	kV	12
Max. operating voltage	kV	12
Rated current	A	400
Rated frequency	Hz	50 / 60
Number of poles	/	3
Rated short-circuit making current (peak)	kA	31.5
Rated short-time withstand current	kA	12.5
Short-time withstand duration	s	4
1-min power frequency withstand voltage (to earth / between poles)	kV	42
1-min power frequency withstand voltage (across isolating distance)	kV	48
Lightning impulse withstand voltage (to earth / between poles)	kV	75
Lightning impulse withstand voltage (across isolating distance)	kV	85
Mainly active load breaking capacity	A	400
Cable charging breaking current	A	10
Mechanical endurance	operations	2000
Operating mechanism	/	Manual
Conductive material	/	Copper (silver-plated contact)
Ambient temperature range	°C	-5 to +40
Application	/	Industrial indoor distribution
Standard compliance	/	IEC 60265, GB 3804

Product Details

Compressed-Air Arc Quenching

This load break switch breaks load current by drawing the arc into a compressed-air column inside the arc-extinguishing tube. When the contacts separate, the moving contact pulls the arc through the tube, where the air flow cools and stretches the plasma until it cannot sustain itself. This method is simple, reliable and requires no special gas filling or vacuum bottles. The arc chutes are accessible for inspection after long service periods, and replacement parts are standardised across most 12kV air-type load switches.

Copper Conductive Path with Visible Isolation Gap

The main current path uses high-conductivity copper bars with silver-plated contact surfaces to keep contact resistance low and temperature rise within limits. When the switch opens, the moving contact drops away from the fixed contact to create a clear, visible air gap. This physical separation gives maintenance crews a direct visual confirmation that the circuit is isolated, which is a requirement in many industrial safety procedures.

Integrated Fuse-Combination Protection

In the fuse-combination version, high-voltage current-limiting fuses mount directly above the switch body. The fuses carry normal load current and clear short-circuit faults inside their rated breaking range. A fuse striker mechanically trips all three phases of the load switch whenever any fuse blows, ensuring full isolation of the faulted transformer. This integration removes the need for separate protective relays and circuit breakers in small distribution substations, reducing both panel size and wiring complexity.

Mechanical Interlock and Safe Operation

The operating mechanism includes a mechanical interlock matrix that prevents unsafe sequences. The switch cannot be closed unless the fuse compartment cover is fully latched, and the cover cannot be opened unless the switch is in the fully open position. The handle itself is spring-assisted, so the operator applies consistent force regardless of switching duty. These features are built into the standard manual mechanism without additional electronic components, which keeps the system reliable in harsh electrical environments.

Compact Footprint for Indoor Substations

The three-pole assembly mounts on a single steel frame with a width of roughly 500mm and a height under 450mm. This compact outline fits standard 12kV switchgear cabinets and cable branch boxes without custom brackets. The fixed mounting holes align with common installation patterns, making the unit suitable for both new switchgear lines and retrofit projects where floor space is already constrained.

Application Scope

This load break switch is intended for indoor 10kV/12kV distribution systems in power stations, industrial enterprises and commercial buildings. It controls power flow to distribution transformers, isolates feeders for cable maintenance, and sections industrial busbars. The 400A rating covers most secondary substation transformers up to about 6.3MVA, and the fuse-combination version extends protection to transformers up to 10MVA depending on fuse selection.

FAQs

What voltage and current ratings does this load break switch cover?

The unit is rated for 12kV maximum operating voltage and 400A continuous current at 50Hz or 60Hz. It can break active load current up to 400A and cable charging current up to 10A. The rated short-circuit making current is 31.5kA peak, and the short-time withstand current is 12.5kA for 4 seconds.

How does the integrated fuse protection work in a load break switch?

In the fuse-combination version, high-voltage current-limiting fuses mount above the switch. The fuses carry normal load current and clear short-circuit faults. When a fuse blows, its striker mechanically trips all three phases of the load switch automatically. This ensures the faulted transformer or cable is fully isolated without needing a separate circuit breaker.

What is the difference between a load break switch and a circuit breaker?

A load break switch is designed to make, carry and break normal load current. It can close onto a short circuit safely, but it cannot break fault current. A circuit breaker can break short-circuit current on its own using advanced arc-extinguishing media such as SF6 or vacuum. Load switches are simpler, lower cost and sufficient for transformer feeder circuits where fuse protection handles fault clearance.

Can this switch interrupt short-circuit current on its own?

No. This load break switch cannot break short-circuit current. Its role is to carry normal load current and to close onto a short circuit without damage. Fault clearance must be provided by the integrated high-voltage fuses in the combination version, or by an upstream circuit breaker. Attempting to open the switch under fault conditions would damage the contacts and endanger personnel.

What maintenance does a compressed-air load switch require?

The unit requires periodic inspection of contact wear, arc-extinguishing tube condition and operating mechanism lubrication. Because it uses compressed air rather than sealed gas or vacuum, the arc chutes are accessible for cleaning and replacement. We recommend checking contact alignment and measuring contact resistance every one to two years, depending on switching frequency. The mechanical interlock should be tested annually to confirm it still blocks unsafe sequences.