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.
At a glance
- 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, and 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. Whether the unit is extensible, with functions that can be added later, is worth deciding at the outset.
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 |
Typical options are the ones buyers most often specify. They are not a list of what is available, which is confirmed per enquiry.
Insulating gas and the EU F gas rules
| Switchgear | Putting into operation with fluorinated gas in the insulating or breaking medium is prohibited from |
|---|---|
| Medium voltage, primary and secondary distribution, up to and including 24 kV | 1 January 2026 |
| Medium voltage, primary and secondary distribution, above 24 kV up to and including 52 kV | 1 January 2030 |
| High voltage, 52 kV up to and including 145 kV and up to 50 kA, gas with a global warming potential of 1 or more | 1 January 2028 |
| High voltage, above 145 kV or above 50 kA, gas with a global warming potential of 1 or more | 1 January 2032 |
Regulation (EU) 2024/573, Article 13(9). The prohibition attaches to putting equipment into operation, not to when it was made, which matters for unused surplus stock. Taking switchgear out of operation in the Union and putting it into operation at another Union site is not treated as putting into operation (Article 13(10)). The regulation provides derogations tied to the outcome of a procurement procedure (Article 13(11) and 13(12)). Whether a derogation applies to a project is a question for the project, not for this page.
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 62271-1 | Common specifications for AC switchgear and controlgear above 1000 V |
| IEC 62271-200 | AC metal enclosed switchgear and controlgear above 1 kV up to and including 52 kV |
| IEC 62271-100 | AC circuit breakers above 1000 V, where the transformer feeder uses one |
| Regulation (EU) 2024/573 | Restrictions on fluorinated gases in new switchgear, see below |
The standard that applies is set by the specification and the destination market. Editions change, so the edition cited in a specification is confirmed in the quotation.
Documents normally requested
| Document | What it evidences |
|---|---|
| Technical datasheet and single line diagram | Ratings, panel functions and the arrangement offered |
| General arrangement drawing | Footprint, height, cable entry and floor fixings |
| Type test report | The design has passed the type tests of its standard, including internal arc where claimed |
| Routine test report | The individual assembly's tests before dispatch |
| Schematic and wiring diagrams | Control, protection and interlocking circuits |
| Operating and maintenance manual | Operation, interlocks and maintenance |
An internal arc classification is only as good as the type test behind it, and it applies to the tested configuration. Ask for the report that matches the arrangement offered.
What we need to quote accurately
| 01 | Rated voltage and network voltage |
| 02 | Configuration: number of ring switches and transformer feeders, and whether it must be extensible |
| 03 | Transformer rating and the protection type wanted on its feeder |
| 04 | Insulation medium, and any destination restriction on fluorinated gas |
| 05 | Manual or motorised operation, and any remote control or monitoring |
| 06 | Cable type and connection arrangement |
| 07 | The network operator's specification, where the unit will be adopted |
| 08 | Quantity, destination, required delivery date and acceptable condition |
Delivery and logistics
Distribution equipment is heavy, and a delivery date is only real once the site is ready for it. The dimensions and weight of the unit offered decide the vehicle, the lifting equipment and the route to the foundation, and they come from the manufacturer's drawing rather than from the rating.
Liquid immersed transformers are usually shipped filled, which affects transport rules and the handling on arrival. Anything crossing a border also carries customs documentation, and where the destination applies its own conformity or energy efficiency rules the paperwork has to match that market rather than the country of manufacture.
Lead times vary widely with rating, specification and manufacturer loading. We state a delivery basis in each quotation for the specific unit offered and do not publish a general lead time we cannot hold.
Common questions
Can a surplus or refurbished SF6 ring main unit be installed in the EU?
The EU prohibition on fluorinated gas in new distribution switchgear up to 24 kV attaches to putting the equipment into operation from 1 January 2026, not to its date of manufacture. Relocating switchgear that is already operating in the Union is treated differently. We check the insulation medium against the destination and the project before quoting any unit.
Related
Request a quote for this equipment
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.