An internal-arc classification belongs to a tested assembly under defined conditions. It is not a universal guarantee for every room, ceiling, duct or field modification. The project must preserve the tested pressure path and prevent hot gases, particles and pressure waves from being redirected toward personnel or critical equipment.
Read the complete IAC designation
IEC 62271-200 applies to AC metal-enclosed switchgear above 1 kV and up to and including 52 kV. The IAC designation must be read with accessibility type, tested sides, arc current and duration. A label such as AFLR describes tested accessibility; it does not state that any installation is safe regardless of room geometry.
Treat the room as part of the pressure system
Identify the initial compartment, flap opening sequence, plenum volume, duct area, bends, supports, external termination and weather protection. Check ceiling height and clearances against the manufacturer’s tested or validated installation instructions. Some designs exhaust into the room through absorbers; others require a closed duct to the outside. These are not interchangeable field options.
Interfaces that require coordinated ownership
- Switchgear-to-plenum joints and pressure-rated fasteners.
- Duct supports and building loads during a pressure event.
- Wall or roof penetration, fire stopping and weather sealing.
- External discharge location, exclusion zone and public access.
- HVAC dampers, smoke detection and room pressure paths.
- Cable trench covers and floor sealing where downward relief is used.
Do not improvise duct geometry
Reducing area, adding sharp bends, using flexible sections or combining exhausts can alter back pressure and opening behaviour. Manufacturer instructions may require a particular minimum room height or external duct arrangement. Where the installation differs, obtain a documented engineering assessment from the switchgear manufacturer; computational fluid dynamics can support analysis but does not automatically replace type-test evidence.
Inspection and handover
Verify flap freedom, assembly direction, seals, fastener torque, duct continuity and the unobstructed outlet. Photograph hidden joints before closure. Mark the external discharge hazard and prevent storage near the outlet. Include the duct and building interfaces in the final walkdown, not only the panel lineup.
Change control
Later additions—cables, roof services, lighting, acoustic panels or ventilation ducts—can obstruct pressure relief. The as-built relief route should therefore be a controlled safety interface. Maintenance must also check corrosion, loose panels, blocked screens and unauthorised penetrations.
Official sources and revision control
- IEC 62271-200:2021+AMD1:2024 official record
- Siemens arcing faults in MV/LV switchgear
- Siemens NXAIR 50 kA catalogue
- Siemens GM-SG selection and application guide
Technical review date: 16 August 2026. Standards and product capabilities can change; confirm the project-specific edition, firmware, options and ordered configuration before engineering or procurement.