DNO: what a distribution network operator does and when you need to apply to one
The company that owns and operates the local electricity cables, substations, and transformers between the national grid and the customer's meter. Not the energy supplier. Any installation that adds generation or significantly raises site demand requires DNO notification or approval before commissioning.
In short
A DNO owns the local cables and substations your installation connects to, not the energy supplier you pay each month. Before commissioning any job that adds generation or raises site demand, check whether G98 notify-after or G99 pre-approval applies.
A Distribution Network Operator (DNO) is the licensed company that owns and operates the local electricity cables, substations, and transformers that carry power from the national transmission network to homes and businesses. Every property in Great Britain sits within one of fourteen distribution districts, each served by one of seven DNOs: Northern Ireland Electricity, SSE, SP Energy Networks, Electricity Northwest, UK Power Networks, National Grid, and Northern Power Grid. The DNO is not the energy supplier a customer pays each month - it owns the wires and decides what load they can safely carry. For an electrical installer, that distinction is the key to knowing whether a job triggers a notification, a formal application, or nothing at all: any work that adds generation or significantly raises the site's maximum demand is connecting to the DNO's infrastructure, and the DNO must be informed or must approve before the system is energized.
What the DNO owns and controls
The DNO is responsible for the network from the high-voltage substation down to the low-voltage service head at each property. That includes the local transformer, the street-level cables, and the cut-out fuse at the meter position. When an installer adds significant load - a heat pump, a bank of EV chargers, or a large commercial system - the DNO's transformer and feeder cables carry the additional current. When a solar PV or battery system exports electricity back through those cables, the same infrastructure is affected in the opposite direction. The DNO holds the authority to refuse a connection or require network reinforcement works before energization is permitted.
Because DNOs operate as regulated regional monopolies licensed by Ofgem, they cannot be changed by the customer or the installer. Ofgem sets how much revenue each DNO can earn, and the cost of running the distribution network is passed through to consumers - approximately 20 to 25 percent of a typical electricity bill covers the local distribution network. Installers working in renewables and lighting and electrical need to account for DNO involvement at the survey stage, because it is geography that determines which operator to contact, not supplier preference.
When a job triggers DNO involvement
Engineering Recommendations G98 and G99, published by the Energy Networks Association (ENA), set the technical boundary between jobs that require prior approval and those that can proceed and notify afterward.
Generation and storage (solar PV, batteries, wind):
Systems under 16 amps per phase fall under G98. The installer can commission the system first, then notify the DNO within 28 days using G98 Form B. No pre-approval is needed. Systems above 16 amps per phase fall under G99, which requires a formal application to be submitted and approved by the DNO before the installation is connected to the network. Most residential solar installations sit within G98; commercial arrays and hybrid solar-plus-battery systems commonly exceed the threshold and fall under G99.
Demand-raising equipment (heat pumps, EV charge points):
The MCS guidance sets two connection scenarios. Where the site's new maximum demand after installation will be 60 amps or less, the installer can proceed and then notify the DNO within 28 days using the relevant ENA form. Where new maximum demand will fall between 60 amps and 100 amps inclusive, the installer must submit an application to the DNO before installation begins. The DNO then has 10 working days to assess supply capacity. Commercial installations with multiple charge points almost always exceed 60 amps and require the pre-application route.
The threshold applies to the combined load of all equipment at the site. A property that already has a heat pump installed may find that adding a 7 kW EV charger tips the total demand past the notify-only boundary even if the charger alone would not.
The two-track process: notify versus apply
The operational distinction is straightforward. Under the notify route (G98 or demand below 60 amps), the installer commissions the system and then submits the appropriate form to the DNO within 28 days. Under the apply-to-connect route (G99 or demand between 60 and 100 amps), the installer submits a formal application before energization. The DNO assesses the request and may require infrastructure reinforcement, which adds time and can require the main contractor to adjust the commissioning programme.
Analysis published by Nesta found that customers in some regions wait an average of 58 days for DNO approvals. For contractors managing multiple active jobs, that lead time needs to be treated as a procurement item: raised at the survey stage, tracked against a target date, and flagged immediately if the DNO asks for more information.
Finding the right DNO
The Energy Networks Association runs a postcode search tool at energynetworks.org that identifies the correct DNO for any address in Great Britain. The first two digits of the property's MPAN - shown on the electricity bill - also correspond to a specific network operator. Northern Ireland is served by NIE Networks and is not within the ENA's postcode tool.
Tracking DNO application status as part of the job record - alongside survey notes, equipment orders, and commissioning dates - keeps it visible to everyone managing the project rather than sitting in one person's inbox. Zigaflow's Jobs feature lets contractors attach application reference numbers and expected response dates directly to the relevant job record, so approval delays surface before they affect the commissioning date.