Switchgear
Ring main units (RMU) for 11 kV to 22 kV networks
Compact medium voltage switchgear for secondary distribution, with switches for the incoming and outgoing ring cables and a protected feeder for the transformer.
- Common rated voltages
- 12 kV and 24 kVfor 10 or 11 kV and 20 or 22 kV networks
- Common configuration
- two ring switches and a transformer feederextensible units add functions
- Transformer protection
- switch fuse or circuit breaker with relayset by the rating and the protection scheme
- Insulation
- gas, air or solidEU F gas rules apply from 2026 up to 24 kV
- Standard
- IEC 62271-200metal enclosed switchgear above 1 kV to 52 kV
A ring main unit sits where a medium voltage cable ring meets a transformer. Two switches connect the incoming and outgoing ring cables, so the ring can be opened and closed around a fault. A third function protects the transformer. The unit is compact, often sealed, and usually installed inside a compact or package substation.
The transformer protection function is the main choice. A switch fuse combination suits smaller transformers. A circuit breaker with a protection relay suits larger ratings and schemes that need more selective protection. Decide at the outset whether the unit must be extensible, so that functions can be added later.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Rated voltage | 12 kV or 24 kV | The network voltage |
| Configuration | Ring switches and transformer feeders, fixed or extensible | The network arrangement and future needs |
| Transformer protection | Switch fuse or circuit breaker with relay | Transformer rating and protection scheme |
| Insulation medium | Gas, air or solid | Footprint, environment and destination rules |
| Operation | Manual, or motorised for remote control | Network automation plans |
| Cable connection | Bushing type and number of cables per function | The cables used on the network |
| Internal arc classification | As proven by type test | Where the unit stands |
| Fault indication and monitoring | Fault passage indicators, remote terminal unit | Network automation |
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 62271-200 | The unit as metal enclosed switchgear, with the internal arc class it was tested to |
| IEC 62271-1 | The ratings common to its ring switches and transformer feeder |
| IEC 62271-103 | The ring switches, as load break switches up to and including 52 kV |
| IEC 62271-105 and IEC 60282-1 | The transformer feeder as a switch fuse combination, and the current limiting fuses in it |
| IEC 62271-100 | The transformer feeder, where it is a circuit breaker rather than a switch fuse |
| Regulation (EU) 2024/573 | Up to 24 kV, new units may not be put into operation in the EU or Northern Ireland with fluorinated gas for insulation or breaking from 1 January 2026; Great Britain has no such rule |
| ENA TS 41-41 | Issue 2, January 2026: ground mounted distribution substation RMUs and extensible switchgear rated 12 to 24 kV, for 11 and 20 kV systems. The Energy Networks Association lists it as replacing TS 41-36 for this equipment |
A unit for adoption by a GB distribution network operator is specified against the operator's own documents built on TS 41-41. In Dubai, DEWA's published distributed generation standards rate 11 kV equipment at 25 kA for 3 s and 63 kA peak, with equipment ratings expressed at 55 °C ambient.
What a ring main unit request needs
- Rated voltage and network voltage
- Configuration: number of ring switches and transformer feeders, and whether it must be extensible
- Transformer rating and the protection type wanted on its feeder
- Insulation medium, and any destination restriction on fluorinated gas
- Manual or motorised operation, and any remote control or monitoring
- Cable type and connection arrangement
- The network operator's specification, where the unit will be adopted
Specification template
Fill it in on screen or by hand, then upload it with your request.
Questions buyers ask
Can a surplus or refurbished SF6 ring main unit be installed in the EU?
Up to 24 kV, the EU prohibition on fluorinated gas in new distribution switchgear applies from 1 January 2026. It attaches to putting the unit into operation, whatever its date of manufacture. Moving a unit that is already in operation in the Union to another Union site is treated differently, under Article 13(10). We check the insulation medium for your destination and project before quoting any unit.