Once a generation project moves out of the domestic-scale G98/G99 sub-50kW space and into Type B, C or D territory, the DNO doesn't simply issue a single approval and let you connect. Instead, it issues a series of operational notifications at defined milestones in the project.
Understanding which notification you need at which stage is essential — you don't have permanent rights to generate until the final one is in your hand.
The four notifications
EON — Energisation Operational Notification
Required for Type C and Type D in Scotland, and Type D only in England. You need this before energising your internal network. In practical terms, it's the DNO's permission to bring your own site infrastructure to life — before any generation happens.
ION — Interim Operational Notification
Required for Type C and Type D in Scotland, and Type D only in England. You need this before synchronising your Power Generating Module for the first time. It's the go-ahead to run the module against the grid, usually as part of commissioning and compliance testing.
LON — Limited Operational Notification
Again, Type C and Type D in Scotland, Type D only in England. A LON is issued if you have a non-compliance issue that isn't resolved within a certain amount of time. It lets the plant operate under restricted conditions while the compliance gap is worked through — but it's not a permanent state.
FON — Final Operational Notification
Applies to all of Types B, C and D when compliance with G99 has been demonstrated satisfactorily. This is the important one: you don't have permanent rights to generate until you have received your FON.
Who issues them?
In most cases the DNO issues these notifications. There's one exception: if you're installing a Large Power Station, National Grid issues some of them.
The Large Power Station threshold isn't uniform across the UK:
- North of Scotland: above 10MW.
- England: above 100MW.
Where each one sits in the project lifecycle
A simplified timeline for a Type C or D project in Scotland (or Type D in England):
- Connection offer accepted, design progresses.
- PGMD drafts submitted (see our separate article on the PGMD).
- EON issued — internal network can be energised.
- ION issued — first synchronisation with the grid.
- Commissioning and compliance testing carried out.
- FON issued once G99 compliance is demonstrated — permanent right to generate.
If compliance issues linger past a defined point during step 5, a LON may be issued so the plant can keep operating (with restrictions) while things are resolved.
Why this matters for project timelines
Each notification is a checkpoint the DNO controls. If any documentation isn't ready — most commonly the PGMD, protection settings, or witness testing outcomes — the notification stalls, and the project stalls with it.
For Type B projects (1MW to under 10MW), the picture is simpler: no EON, ION or LON is involved, but the FON is still required before you can operate with permanent rights, and the PGMD still underpins it.
When to start planning for these
If your project is 1MW or larger, treat operational notifications as a workstream in their own right from the moment the connection offer is accepted — not something to figure out at commissioning. The evidence they depend on (protection settings, simulation studies, type-test references, PGMD content) needs to be assembled progressively through the build.
Projects that leave this to the end are the ones that miss their energisation dates.