Actom Ring Main Unit (RMU) – Oil-Insulated Medium Voltage Switchgear

The Actom Ring Main Unit (RMU) is a durable, oil-insulated medium-voltage switchgear solution engineered for safe, flexible, and reliable distribution up to 36kV. Designed for networks where continuity of supply and operator protection are essential, this RMU provides internal arc-rated performance and a sealed-for-life stainless-steel enclosure. Its compact footprint and robust construction make it suitable for utilities, substations, industrial plants, and renewable energy projects requiring dependable load switching and transformer protection.

The Actom RMU is available in multiple configurations, including Type A, B, and C units, allowing engineers to tailor protection methods to network requirements. It supports both T-OFF fused and circuit-breaker fused switching, while optional EFI (Earth Fault Indicator) and CT (Current Transformer) modules provide enhanced monitoring, fault visibility, and improved network management.

Key Features of the Actom RMU

• Voltage capability up to 36 kV

• Oil-cooled insulation (K3/AF)

• T-OFF fused or circuit-breaker fused switching

• Air-insulated cable entry design

• Two cable terminations

• EFI and CT optional add-ons

• Fully internal arc-tested protection

• Compatible with copper and aluminium transformer windings up to 1250 kVA

• Metal-enclosed, sealed-for-life stainless steel construction

Benefits of the Actom Ring Main Unit

The Actom Ring Main Unit provides strong operational performance, particularly in medium-voltage environments where reliability and safety are critical.

• Operator Safety
  Its internal arc-rated design helps protect personnel while maintaining system uptime.

• Compact Design
  Suitable for both indoor and outdoor applications with limited space.

• Flexible Protection Methods
  Choose between fuse-based or circuit-breaker-based protection to match system needs.

• Stable Insulation Performance
  Oil-insulated cooling ensures reliable operation under varying load conditions.

• Low Maintenance Requirements
  Hermetically sealed pressure systems minimise servicing, reducing lifecycle costs.

Applications of the Actom Ring Main Unit

This RMU is used across a wide range of distribution networks, including:

• • Utility substations

  • Commercial and industrial facilities

  • Renewable energy generation sites

  • Rural and urban medium-voltage distribution systems