Schneider SM6-24 Air Insulated Medium Voltage Switchgear

SM6-24 air insulated medium voltage switchgear is a metal-enclosed, modular 24 kV cubicle range from Schneider Electric that combines air-insulated busbars with sealed-for-life SF6 switching and earthing units to deliver compact, low-maintenance distribution and protection functions for primary and secondary substations. This article covers the SM6-24 cubicle family — its construction, functional variants (DM1, CM, PM, QM, GBC and related types), circuit-breaker and switch-fuse ratings, internal arc (IAC) classification, applicable IEC standards, and the selection criteria buyers need before specifying equipment for a project. It is written for engineers, EPC contractors, and utility procurement teams sourcing MV switchgear for the Middle East and Gulf region including Egypt and Saudi Arabia, North Africa, CIS countries, and Sub-Saharan Africa, where SM6 cubicles have an extensive installed reference base.

What Is SM6-24 Air Insulated Switchgear?

SM6-24 belongs to Schneider Electric’s SM6 modular MV cubicle platform, which is manufactured with SF6 or vacuum switching technology and is designed for a 30-year service life. The switching and earthing parts sit inside a sealed-for-life SF6-filled unit, while the surrounding cubicle structure and busbar compartment use air as the primary insulation medium — hence the “air insulated” designation used in the manufacturer’s own catalogue naming for the SM6 range. This hybrid approach keeps the switching chamber maintenance-free while allowing straightforward busbar extension and connection work in the field.

Globally, Schneider Electric reports more than 1,700,000 SM6 cells installed worldwide, supported by over 2,500,000 SF6 medium voltage cells supplied by the company across its product history. The platform’s development timeline shows more than 300,000 SM6 cells in service by 1989 and over 1,500,000 by 2015, reflecting a mature, field-proven design rather than a recent introduction.

Cubicle Types and Functional Variants

The SM6-24 range is built from functional units that can be combined side by side to build a complete switchboard. Key cubicle designations referenced in the manufacturer’s operating and maintenance documentation include:

• DM1, DM1-W, DM1-Z — withdrawable circuit-breaker cubicles, where the circuit breaker can be racked out and racked in for isolation and maintenance.
• DM2, DMV, DMVL — additional circuit-breaker and disconnector cubicle variants used for incoming/outgoing feeder and coupling functions.
• CM, CM2, PM, QM, QMC, QMB, TM — fuse-combination and fused-switch cubicles for transformer protection, each with fuse-status indication and MV fuse replacement procedures defined in the manufacturer’s manual.
• GBC-A, GBC-B — cubicles with dedicated fuse replacement procedures, typically used in ring/feeder configurations.
• CVM — a metering/voltage variant included in the fuse-replacement instructions alongside CM/PM/QM types.

Each cubicle uses a three-position switch structure (open / closed / earthed) to prevent incorrect switching sequences, and the earthing switch has a full making capacity design, giving operators a mechanically interlocked, visually confirmed switching sequence.

High-Performance Breaking Devices

The SM6 range integrates SF1 and/or Evolis breaking devices, rated at 630 A and 1250 A, with breaking capacities of 16 kA and 25 kA. Note that the Evolis breaker option is not available at the 36 kV voltage level, meaning full breaker choice flexibility applies specifically to the SM6-24 platform.

Internal Arc (IAC) Classification

Internal arc withstand is a critical safety differentiator for MV switchgear specifiers. The SM6 range offers both 3-sided and 4-sided internal arc protection:

• IAC: A-FL (3-sided arc protection) — for SM6-24, rated at 12.5 kA 1s, 16 kA 1s, and 20 kA 1s; for SM6-36, rated at 16 kA 1s.
• IAC: A-FLR (4-sided arc protection) — for SM6-24, rated at 12.5 kA 1s, 16 kA 1s, and 20 kA 1s.

Gas evacuation can be routed downward for all units, or upward specifically for SM6-24 cubicles, giving substation designers flexibility for cable basements versus overhead exhaust ducting.

Selection Criteria for Buyers

When specifying SM6-24 air insulated medium voltage switchgear, evaluate the following:

1. Rated short-time withstand / IAC class needed — determine whether 12.5 kA, 16 kA, or 20 kA 1s arc withstand is required based on upstream fault level and personnel safety requirements (3-sided vs. 4-sided protection).
2. Breaking device type — confirm whether SF1 or Evolis vacuum circuit breakers suit the application, and required current rating (630 A or 1250 A) and breaking capacity (16 kA or 25 kA).
3. Functional unit mix — select DM1/DM2/DMV/DMVL for circuit-breaker feeders, CM/PM/QM/QMC/TM/GBC types for fused transformer protection.
4. Withdrawable vs. fixed design — DM1-W and DM1-Z variants allow the circuit breaker to be racked out for maintenance without de-energizing the entire busbar.
5. Monitoring and connectivity — compatibility with PowerMeter, Easergy P3/Sepam protection relays, VIP self-powered protection relays, and Easergy TH110 temperature sensors for condition-based maintenance.
6. Gas evacuation routing — downward or upward exhaust depending on switchroom layout.
7. End-of-life compliance — dismantling and SF6 gas recovery service aligned with IEC 62271-4:2013.

Spec Comparison Table

Applications

SM6-24 cubicles are used in primary and secondary distribution substations, industrial plants, data centers, airports, and utility ring main points where compact, low-maintenance MV switching combined with fused transformer protection is required. Reference installations documented by the manufacturer span airports, hospitals, universities, cement plants, and utility distribution companies across multiple regions, including projects in Egypt and Saudi Arabia. This global reference base supports specification confidence for new-build and retrofit projects in the Middle East and Gulf region including Egypt and Saudi Arabia, North Africa, CIS markets, and Sub-Saharan Africa.

Standards Compliance

SM6-24 cubicles are designed in accordance with IEC standards applicable to metal-enclosed MV switchgear with vacuum circuit breakers up to 24 kV. End-of-life dismantling and SF6 gas recovery follow IEC 62271-4:2013, alongside applicable local regulations such as EU Regulation No 517/2014 on fluorinated greenhouse gases. Because the switching units contain SF6 — a potent greenhouse gas — recovery, reclamation, or destruction of the gas is mandatory prior to disposal, and dismantling must only be performed by certified personnel.