G98 vs G99: DNO applications without the wait

G98 covers small generators up to 16 amps per phase, which is 3.68 kW on a single-phase supply: install it, commission it, then notify the Distribution Network Operator (DNO) within 28 days. G99 covers anything larger: apply to the DNO and get approval before you commission. Pick the wrong one, or forget the paperwork, and a finished job sits unpaid while everyone waits.

The two Engineering Recommendations are published by the Energy Networks Association (ENA). This post is about the practical difference, and about keeping the application moving alongside the install rather than after it.

The dividing line is the output of the generating equipment, which for solar means the inverter, not the panels. Up to 16 A per phase is G98. Above it is G99, which then has its own bands by size and connection type.

Two traps catch people. Existing generation on the site counts towards the total, so adding a battery with its own inverter to a 3.68 kW array can push the premises into G99. And the threshold is about inverter output, not panel capacity: a 5 kWp array on an inverter capped at 3.68 kW is a G98 job, which makes inverter choice a design decision. Confirm the current documents on the ENA's site before relying on any of this.

For a single premises within the G98 limit you do not need permission. You install the system with type-tested equipment, commission it, and send the DNO the G98 notification within 28 days of commissioning. The notification carries the installer's details, the customer's details, the site, the equipment and its type-test reference, and the commissioning date.

The 28 days is the whole of the flexibility. Miss it and the install is unregistered, which surfaces later when the customer applies for the Smart Export Guarantee and the supplier asks for the DNO paperwork. If one job covers multiple premises in the same area, G98 requires an application before the installations rather than a notification afterwards, because the combined effect on the local network matters.

Above the threshold the DNO has to assess whether the network can take the export before anything is connected. That means an application with a single-line diagram, a site plan, the inverter's type-test evidence, the proposed capacity and the export arrangement. The DNO responds with an approval, sometimes with conditions such as an export limit, or with a connection offer if network work is needed.

How long it takes depends on the DNO and the size of the job. A straightforward domestic G99 application is usually answered within the DNO's published timescale, often up to 45 working days; anything needing a network study takes longer. Your DNO publishes its own timescales, and they are the ones to plan against.

The wait itself is not the problem. The problem is starting it too late: surveying in March, quoting in April, applying in June and then putting the install on hold. Three habits keep the job moving.

• Apply the day the survey confirms the size. Whether the customer has signed yet or not, an application costs little and the clock starts.
• Use type-tested inverters. Equipment on the ENA's type-test register needs no separate compliance evidence, which is the most common reason an application bounces.
• Design to the threshold when it is honest to. Where the customer's use fits a 3.68 kW export, a G98 design with export limitation avoids the wait entirely. Where it does not, say so and apply.

The application is a task with a status, a date and a document, and it belongs on the job, not in someone's inbox. The Solar installer trade in TradeYoke is in pilot with real installers and treats it that way: a G98 or G99 connection assessment on the job, DNO contacts by region so the right operator is a click away, the type-test documents and single-line diagram attached, and a boundary map of the site. The solar installer page covers the pilot.

When the approval arrives it is filed with the job, and it goes into the handover pack described in the MCS certificate post. The customer sees the status without ringing, which is most of what they wanted.

Jobs that wait on paperwork are also jobs that wait to be paid. A deposit at booking and a pay link on commissioning, as described in how tradespeople get paid the same day, keep the cash moving while the DNO does its work. Pay links are part of the Premium plan and the customer portal is part of Ultimate on the pricing page; pilot trades are priced with the pilot businesses. Installers who also do the electrical certification will find the electrician page useful too.