Every DNO, one data format: a guide to UK grid operators for connection engineers
If you file grid connections in the UK, you already know: there is no single format. Every DNO has its own portal, its own templates, its own way of expressing the same technical data.
The six DNOs
The UK distribution network is split between six licensed operators:
- UK Power Networks (UKPN) — South East, East of England, London. Three licence areas under one brand.
- National Grid Electricity Distribution (NGED) — Midlands, South West, Wales. Rebranded from Western Power Distribution in 2023 after National Grid acquired it from PPL Corporation.
- Northern Powergrid — Yorkshire, North East England.
- SP Energy Networks (SPEN) — Central and Southern Scotland (SP Distribution) plus Merseyside and North Wales (SP Manweb). Two licence areas.
- SSE Networks (SSEN) — North of Scotland and South of England. Two geographically separate licence areas.
- Electricity North West (ENW) — North West England. Single licence area.
Above them sits NESO (National Energy System Operator), which took over from National Grid ESO in October 2024. NESO manages the 400kV/275kV/132kV transmission network and handles connections above 132kV directly.
The connection process
For generators above the G98 threshold (>3.68kW single-phase), you file a G99 application:
- Pre-application — initial enquiry to the relevant DNO with site location, technology type, and requested capacity.
- Stage 1 feasibility — DNO assesses whether the local network can accommodate the connection.
- Stage 2 detailed design — full grid impact study. The DNO issues a Connection Offer (Formal Offer Letter) within 65 working days for straightforward applications.
- Statement of Works — details the civil and electrical works required on the DNO side.
- Design Acceptance — DNO signs off the applicant's plant design before energisation.
For small installations under G98, it is a simplified notification — the installer notifies the DNO within 28 days of commissioning.
What makes this painful for engineers
Every DNO uses different forms, portals, and document templates. UKPN has one online portal. NGED has another. SSEN has a third. The data you submit is essentially the same — site coordinates, single-line diagram, protection settings, export capacity — but the format changes every time.
Connection Offers arrive as PDFs with no machine-readable structure. Your engineer manually re-enters parameters from the PDF into the project's Excel model. A misread digit — 250 MVA instead of 315 MVA — propagates through the entire protection coordination study.
Protection settings vary by DNO. Even where ENA Engineering Recommendation G99 is the common standard, each DNO interprets relay settings and export limiting requirements differently.
Queue management is inconsistent. NGED and SSEN in particular have had multi-year backlogs for HV connections. Stage 1 to Stage 2 progression timescales vary significantly, and some DNOs request additional information not covered by the standard G99 form.
The regulator's push
OFGEM regulates all DNOs under the RIIO-ED2 price control (2023-2028). Their 2023-2024 Connections Action Plan pushed DNOs to publish queue data publicly and reduce backlogs. ENA published G99 Amendment 7 in 2023 to address battery storage and hybrid plant connection rules.
But none of this standardises the data format. Each DNO still issues its own Connection Offer template, its own Statement of Works format, its own protection settings schedule.
What this means for your workflow
If your firm files connections across multiple DNO areas, you are maintaining separate data extraction workflows for each one. The same rated short-circuit current appears in six different formats across six different PDFs.
noda normalises all of them into one canonical schema. Drop the Connection Offer from UKPN, the Statement of Works from NGED, the protection schedule from SSEN — the system maps every field to the same structure, flags inconsistencies, and regenerates your schedule of parameters from structured data.
Book a free demo call — we will look at your actual DNO files and show you the mapping.
Published by Pica Ovidiu. noda builds the data layer for grid engineering.
