Medium-Voltage Switchgear: Frequently Asked Questions

An RMU is a compact medium-voltage switchgear assembly used at defined points in a distribution network to provide switching, sectionalising and protection functions. Its particular functions depend on the installed modules and network design.

AIS uses air as an insulation medium between relevant live parts and within defined clearances. Product designs may combine air-insulated construction with a vacuum circuit breaker for current interruption.

The terms describe different equipment arrangements. An RMU commonly serves compact secondary distribution switching/protection functions, while an AIS lineup can serve more extensive primary distribution configurations. Selection depends on switching functions, project SLD, ratings and site requirements.

A vacuum circuit breaker uses a vacuum interrupter to interrupt electrical current under designed operating conditions. The device's application is subject to rated voltage, current and breaking duty.

Rated current relates to continuous normal-load duty. Fault or short-circuit current describes abnormal network conditions and requires separate withstand and interruption ratings.

No. They are distinct equipment categories; compare their switching/protection functions, mechanical layout and approved project requirements.

It denotes tested performance against specified internal-arc criteria for defined equipment arrangements. Read the precise classification, test scope and installation conditions rather than relying on the term alone.

An ingress protection rating describes defined degrees of protection against solid objects and water under the relevant test criteria. It is not a standalone guarantee of suitability for any environment.

Compatible RMU models and configurations may be integrated with motors, status signals, RTUs and communication equipment to enable specified remote monitoring and control. Confirm the full interface and protocol design.

C-SEC has publicly discussed development of F-gas-free medium-voltage technology. The development status and any commercial availability must be checked against formal product announcements. The presently listed RMUs include SF6-insulated categories.

It is an integrated enclosure-based distribution solution that can combine MV switchgear, transformer and LV equipment as defined in the supply scope. Civil work, cable connections, testing and commissioning still require project planning.

System voltage, rated current, fault level, SLD/function-module requirement, indoor/outdoor conditions, protection/automation requirements, location, standards and delivery schedule.

No assumption should be made. Ask C-SEC for the evidence applicable to the proposed model and configuration.

Where C-SEC has released an approved GA publicly, it will be in the technical library. For controlled or project-specific drawings, submit a document request.

Use Ask an Engineer for pre-sales application questions and Service & Support for assistance with existing equipment. Include the model, installation site and relevant document revision where available.