Every few weeks someone asks me whether they really need to tell the DNO about a small solar job, a battery retrofit or a 7kW charger. Yes. It's a legal requirement, it's part of the MCS standard and it protects you and your customer. Here's what the rules actually say.
This post covers Great Britain. Northern Ireland has its own regulations and network operator (NIE Networks), so check their process for jobs there.
What is the DNO?
The Distribution Network Operator (DNO) owns and runs the local electricity network: the substations, cables and overhead lines between the national grid and the cut-out in your customer's meter cupboard. There are six DNO groups in GB, plus several smaller independent network operators (IDNOs). Digits 9 and 10 of the customer's MPAN tell you which one.
The DNO isn't the energy supplier. The supplier sends the bills. The DNO looks after the wires.
Why notification exists
Low-voltage networks were designed for power flowing one way. Solar, batteries and V2G chargers push power back, and EV chargers and heat pumps add large, long-running loads. One install rarely matters. Dozens on one street do.
The DNO needs to know so it can:
- Keep the network within its limits. More generation on a feeder can lift the voltage, and more load can push cables and transformers towards their ratings. ENA lists supply overload, damage to supply equipment, power quality and the adequacy of earthing as reasons a network operator may need to be involved before an EV charger or heat pump goes in.
- Plan and model the network. ENA says missing notifications mean incomplete modelling, stressed assets and poorly targeted reinforcement, paid for by consumers.
- Keep line workers safe. ESQCR requires small generators to disconnect themselves when the DNO's supply is lost. That's the loss-of-mains (anti-islanding) protection in G98 and G99. It's there so a section of network the DNO thinks is dead isn't being fed back from someone's inverter.
What the law says
The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR), regulation 22, says that no one may install or operate a source of energy that can run in parallel with the network unless they have the right equipment, personnel and procedures to prevent danger, it meets British Standards, and they agree specific requirements with the DNO.
There's an exception for small sources: up to 16A per phase at low voltage, set up to disconnect itself when the DNO's supply goes off. For those, you don't have to agree requirements in advance, but the installer must make sure the DNO is advised. The regulation says before or at commissioning. A 2008 HSE exemption, which G98 refers to, allows up to 28 days after commissioning.
Regulation 26 lets a DNO that isn't satisfied an installation is safe require remedial work and, if it isn't done, disconnect or refuse to connect the supply. G98 itself warns that not following its procedure may lead to disconnection under ESQCR 26.
Which jobs need it
- Solar PV: always.
- Battery storage: always. A battery inverter that can export counts as generation.
- EV chargers: always, as a notification or an application.
- Heat pumps: always, as a notification or an application.
- Wind and other generation: always.
MCS says you must notify the DNO for heat pumps, solar PV, wind and battery storage. ENA says every EV charger or heat pump added to an existing property must be notified.
G98: fit and inform within 28 days
EREC G98 covers fully type-tested micro-generators where the total on the installation is no more than 16A per phase. That's about 3.68kW on single phase or 11.04kW on three phase. For a single premises it's "fit and inform":
- install and commission;
- send the DNO the G98 Installation Document (Form B) no later than 28 days after commissioning, counting the commissioning day as day one;
- send one form per premises, signed by the customer and the installer.
The trap: if you've commissioned, or plan to commission, other G98 installs in the same close geographic area within 28 days, you must talk to the DNO first using the multiple-premises process (Form A).
G99: apply before you connect
Anything over 16A per phase in total, or kit that isn't fully type tested, goes under EREC G99. You apply first and wait for the DNO's answer before you connect.
The 16A is the total of all the generation on the installation. MCS's solar standard gives the example of a 3kW PV system and a 3kW battery on the same single-phase supply: together they're over 16A, so G99 applies. Adding a battery to an existing PV system can tip a G98 job into G99.
If the system can generate more than the DNO will accept on export, a G100 export limitation scheme can cap it. That needs the G100 information as well.
EV chargers and heat pumps: connect and notify, or apply
These are loads, so G98 and G99 don't apply (unless it's a V2G charger that can export). ENA's process for existing properties works like this:
- Connect and notify. If the maximum demand of the premises, including the new load, is 60A per phase or less and the supply is known to be adequate, with no safety concerns, you install first and notify the DNO within 28 days.
- Apply to connect. Apply first if demand will be over 60A per phase, or if the cut-out looks unsafe or damaged. The same applies if you're unsure of the supply capacity, it's a looped supply, an upgrade is definitely needed or it's unmetered. For new maximum demand between 60A and 100A, ENA says the network operator will confirm within 10 working days.
ENA also points to BS 7671 regulation 132.16 (additions and alterations) and the Distribution Code.
ENA asks installers to use ENA Connect Direct for these. It applies the DNOs' decision rules and can approve straight away when the checks pass, or escalate to the DNO when they don't.
What happens if you don't?
- You're breaking the law. ESQCR regulation 22 puts the duty on the installer. I won't quote penalties here; take proper advice if you're in that position.
- The installation can be disconnected. Under ESQCR regulation 26, a DNO can require remedial work and disconnect if it isn't done.
- You're outside MCS. MIS 3002 says the MCS contractor must make sure the installation complies with ESQCR and must do the G98 or G99 notification itself.
- The customer can struggle to get export payments. Ofgem's SEG rules require MCS (or equivalent) certification, an export meter and an export MPAN. Suppliers can also ask for more. National Grid says energy suppliers ask customers for a DNO acceptance letter, and Octopus lists a letter or email from the DNO approving the new MPAN.
- The customer comes back to you. If they're asked for the DNO paperwork when selling the house or switching export tariff, you're the first call, and it's much harder to sort years later.
The homeowner angle
Your customer won't read G98, but they'll need the paperwork. At handover, give them the MCS certificate, the commissioning paperwork and the DNO's acknowledgement or acceptance. Homeowners: ask your installer for the DNO confirmation and keep it with the house documents.
Making the paperwork quicker
CircuitHQ searches the ENA register for inverters, batteries and other generation devices. It fills in the ENA reference, compliance status, kW, phases and G98/G99 type-test status where the field is blank. It prepares the G98, G99 and G100 forms from the job.
For G98 and G99 solar and battery applications where every device is on the ENA device register, and EV chargers, under 17kW per phase, you review the application and press Submit to send it to ENA Connect Direct from the app. G100 or export-limited setups, and changes to existing applications, still get prepared forms and a draft email to the DNO for you to check and send yourself. The DNO still decides.
More on ENA Connect Direct submission, G98 vs G99 and DNO forms.
Phillip Mills, Director, PPM Electrical Ltd