What Is an SF6 Load Break Switch?
An SF6 load break switch (LBS) is a medium-voltage switching device used primarily in underground distribution networks and ring main units (RMUs). It combines the switching capability needed for load management — opening and closing circuits carrying normal load current — with the compact size and maintenance-free operation that SF6 gas insulation provides.
The key distinction from a circuit breaker: a load break switch can handle normal currents (up to 630A) but cannot interrupt high-magnitude fault currents. When a fault occurs, protection is provided by the upstream circuit breaker or fuse, not the LBS itself.
NAIJI Electric manufactures SF6 load break switches as standalone units and as integrated components in our ring main units, serving utility distribution networks across 30+ countries.
How SF6 Load Break Switches Work
The switching contacts are enclosed in a sealed stainless steel chamber filled with SF6 gas at a pressure of 0.3-0.5 bar (gauge). When the switch opens under load, a small arc forms between the separating contacts. The SF6 gas rapidly absorbs the arc energy and extinguishes it, typically within 20-50 milliseconds.
The sealed gas compartment serves dual functions: SF6 insulates the energized components from the grounded enclosure (allowing compact dimensions), and it quenches the switching arc (allowing safe load interruption without external arc-quenching mechanisms).
Typical Ratings
| Parameter | 12kV LBS | 24kV LBS | 36kV LBS |
|---|---|---|---|
| Rated Voltage | 12kV | 24kV | 36kV |
| Rated Current | 400A / 630A | 400A / 630A | 400A / 630A |
| Short-Time Withstand | 20kA / 1s | 20kA / 1s | 20kA / 1s |
| Making Capacity | 50kA peak | 50kA peak | 50kA peak |
| Mechanical Life | 5,000 operations | 5,000 operations | 5,000 operations |
| Service Life | 30 years | 30 years | 30 years |
Applications
Ring Main Units (RMUs): The primary application. In a typical RMU, two SF6 load break switches provide the ring connections (incoming and outgoing cables) while a circuit breaker or fuse-switch provides transformer protection. This combination delivers reliable underground distribution at minimum cost.
Compact Substations: SF6 LBSs in packaged substations combine the switch, transformer, and low-voltage panel in a single weatherproof enclosure. Ideal for urban distribution where space is limited.
Industrial Networks: Factory distribution systems use SF6 LBSs for bus sectionalizing and transformer switching where fault interruption is provided by the main incoming breaker.
SF6 Environmental Concerns
SF6 is one of the most potent greenhouse gases — its global warming potential is 23,500 times that of CO2, and it persists in the atmosphere for 3,200 years. While the quantity in a single load break switch is small (typically 0.5-2 kg), the cumulative impact of millions of installed units is significant.
Regulatory pressure is mounting: the EU F-Gas Regulation is phasing down SF6 in new switchgear installations, and similar policies are emerging in other markets. NAIJI Electric is actively developing SF6-free alternatives using vacuum and clean-air technology.