WikiProject Power networks/Great Britain

From OpenStreetMap Wiki
Jump to: navigation, search

This page describes the power network in Great Britain but not the island of Ireland (which has a separate, integrated power grid across Northern Ireland and the Republic of Ireland). It's intended as a guide to accurately mapping the power network from aerial photos and by eye.

You can find a specialised map of power infrastructure in OSM on OpenInfraMap.


The electricity network in Great Britain is split into two sections:

The transmission network consists of 400kV and 275kV power lines, and their associated substations. It's run by National Grid in England, and Scottish Hydro and Scottish Power in Scotland. It also includes the various interconnector cables which move power between Great Britain and Ireland and France using high voltage DC. Interconnectors are currently being constructed to Norway and Belgium.

The regional distribution networks distribute electricity from the National Grid to homes and businesses. There are 14 distribution network areas, currently operated by six different companies (Electricity North West, Northern Powergrid, Scottish and Southern Energy, ScottishPower Energy Networks, UK Power Networks, and Western Power Distribution), referred to as Distribution Network Operators or DNOs.

Power Lines

Voltage Network Notes Appearance
400kV Transmission The National Grid. The vast majority, if not all, of these power lines are already mapped in Great Britain from NPE or OS. Large, tall pylons
132kV Distribution The voltage which National Grid supplies to distribution networks. Also the voltage at which some larger onshore wind and solar farms supply their power to the distribution network. Smaller pylons with 6 cables.

Sometimes tall pitchfork-shaped poles with 3 cables.

66kV Mostly used to supply substations in sparsely-populated rural areas and in large cities. This voltage is only used in the Northern Powergrid and Western Power Distribution (South Wales and West Midlands) distribution network areas. Fairly tall, obvious poles with 3 cables. Occasionally small pylons with 6 cables, often interspersed with larger poles.

Few, if any, lines branching off. Cables are clearly visible in good aerial photos at certain angles.

If a line goes between substations (and it's not a higher voltage), it's very likely to be 33 or 66kV.

33kV The most common intermediate distribution voltage in many areas. Most 132kV substations output 33kV. Smaller wind and solar plants often connect to the distribution network at 33kV.
25kV Used for catenary railway electrification only. If a power line doesn't go to a railway traction substation, it's probably not 25kV. Smaller poles. Multiple cables may not be obvious from aerial photography. Rural 11kV networks are usually a web of lines with many branches.
11kV A final-level distribution voltage which will probably supply your small local substation before being stepped down to 230V. 11kV is much more common.
230/400V Standard mains voltage for direct distribution to customers.

If you see a power line tagged with a voltage which isn't in the above table, it's likely to be wrong. (But some offshore wind farms use unusual voltages for their "export" cables.)

In the vast majority of cases, if a power line has three wires, it's a single three-phase circuit (circuits=1, cables=3). If it has six wires, it's two separate circuits (circuits=2, cables=6). The thin ground wire often found at the top of pylons is not included in the number of cables.

Power lines at 33kV and above are often run in pairs (either two lines running side-by-side, or as two circuits on the same set of poles/towers), or as a ring around several substations, to provide redundancy in case of the failure of one line. Such redundant lines are uncommon at lower voltages.

Power Line References

Power lines at 33kV and above have short (2-4 character) alphanumeric reference numbers, such as "4VF". Poles/pylons along these routes are then numbered "4VF-1" etc. These are sometimes surveyable on the poles themselves, and can be added to the ref=* tag.

Subsea Cables

A subsea cable marker visible on Bing imagery

Subsea power distribution cables are common around the UK, especially in the Scottish islands. These are usually at 33kV, though a few 132kV and 11kV cables exist. They can sometimes be identified from aerial photos when a reasonably large power line stops dead right by the sea. You'll usually see a diamond-shaped cable marker on the shore, and if you're very lucky this too can be spotted on the aerial photography.


Waltham Cross Substation, a 400/275kV air insulated transmission substation

Substations should be tagged as power=substation. If a substation is connected to the National Grid (i.e. its maximum voltage is 275kV or 400kV), it should be tagged as substation=transmission. Otherwise, it should be substation=distribution, to keep the usage of these tags in line with the standard terminology used in Great Britain.

The name=* tag should contain the name of the substation, if known, such as "Waltham Cross Substation". It shouldn't contain the voltage, reference, or any other information - use other tags for that. As always, if you don't know the name, there shouldn't be a name tag.


The voltage=* tag should be used to denote the voltages used in the substation, in volts. For transmission and larger distribution substations, the maximum voltage used should be easy to see from connecting power lines, but it may not be possible to tag the voltage of every substation.

Voltage can be inferred from aerial photos by the appearance of power lines and the spacing of busbars, and it's possible to pick up a bit of a knack for this. If a substation has visible busbars or power bays, it's unlikely to be less than 33kV.


Transmission substations will have a maximum voltage of 400kV or 275kV. Most, but not all, transmission substations are also grid supply points (GSPs), which is where the transmission voltage is stepped down by large transformers (sometimes known as SGTs or Super Grid Transformers) to 132kV for handoff to the distribution network.

These substations should be tagged with operator=National Grid PLC in England, and the appropriate operator in Scotland.

Traditional transmission substations, such as Waltham Cross, are very obvious from the large network of air-insulated busbars and switches.

Gas Insulated Switchgear at St John's Wood substation

More modern transmission substations may use Gas Insulated Switchgear (GIS) for part or all of their switchgear, especially if they're space-constrained. This looks quite different from the old air-insulated switchgear, and most of it is enclosed within buildings. These buildings can be tagged with power=switchgear, gas_insulated=yes.

Some transmission substations also share a site with a distribution substation, which is frequently referred to by the same name. These are administratively and technically separate entities, run by different operators. The easiest way to tag these, unless you're sure what you're doing, is as a single site with all voltages in the voltage=* tag.


Once power is handed over to the distribution network from the National Grid, it will probably pass through several substations before reaching your home.

Generally, the 132kV will be stepped down to 33kV (sometimes 66kV) for the first intermediate stage of distribution. These substations are sometimes referred to as "grid" substations or bulk supply points (BSPs). A rural 132kV substation can service a radius of several hundred km, while London's West End has three 132kV substations within 5 minutes' walk of each other, fed by underground tunnels.

Closer to the consumer, the voltage will then be stepped down to 11kV or 6.6kV at a "primary" substation for the next stage of distribution. In most areas, primary substations are reasonably-sized substations, but in very rural areas, they can be pole-mounted transformers.

Finally, a "secondary" substation (sometimes just a transformer on a pole) will drop it down to 230V for domestic consumption.

Industrial customers may be fed power at 11kV, or occasionally at even higher voltages.

Grid substations and some primary substations are generally fairly obvious on aerial imagery. Secondary substations are much less obvious and will need local knowledge to map.

It's common for multiple levels of substation to be located on the same site - so a 132kV substation might have a primary substation as well. It will output 33kV to send to other primary substations as well as 11kV for more local use. These are logically separate substations to the distribution network operator, they will often be physically separated on site, and may have separate entrances. However, it's not really worth tagging these differently, and voltage=132000;33000;11000 is acceptable here.

Power Plants

All except the smallest power generators (say, less than 100kW) should be primarily tagged as power=plant, as this is the main tag for power generation. If you wish, you can then tag the individual generating elements as power=generator.

In most cases, this involves drawing an area around the entire site (generally the fenced boundary) and tagging it with power=plant, plant:source=*, and ideally plant:output:electricity=* and operator=*.

Wind Farms

Onshore wind farms should be tagged as a dispersed power plant using a type=site relation.

Most offshore wind farms at the moment are tagged as areas, as this allows the appropriate Seamark tags to be applied as well.

Solar Farms

Draw an area around the perimeter (there's almost always a fence), and tag it as power=plant, plant:source=solar. If there are multiple perimeters which comprise a solar farm, use a multipolygon with the same tags.

If you have the patience, you can then draw areas around each individual group of solar arrays and tag them as power=generators, but this is much less important than the power=plant tag.