How to apply for a G99 connection
Nine stages, four possible application forms, and a decision your installer usually makes for you without explaining it. This is what the process actually involves, taken from the Energy Networks Association’s own annexes rather than from a DNO’s marketing page.
You apply, the network operator assesses, and only then does anything get installed. That sequence is the whole point of G99 , and it is what separates it from the G98 notify-afterwards route.
For a domestic system the form is almost always A1-1 — for total capacity under 50 kW three-phase or 17 kW single-phase — or A1-2 where one of the simplified small-generation procedures applies.
Under those simplified procedures the operator must respond within 10 working days, and your commissioning date must fall between 10 working days and 3 months from applying.
The nine stages
G99’s annex sets out the process as a checklist, which is more than most DNO websites do. Reproduced here as a summary, in plain language.
| Stage | What happens | Form |
|---|---|---|
| 1. Find an installer | Outside G99’s scope entirely | — |
| 2. Discuss with the DNO | Optional but sensible on anything unusual | — |
| 3. Submit application | The operator assesses whether network studies or reinforcement are needed, and whether it wants to witness commissioning | A1-1, A1-2, A1-3 or the standard form |
| 4. Application acceptance | If reinforcement is needed you get a connection offer. Construction begins only once you accept it | — |
| 5. Compliance | Evidence the equipment meets the standard. One report per type or model | A2-1, A2-2 or A2-3 |
| 6. Construction and commissioning | If the DNO does not witness, submit within 28 days. If it does, forms are signed on the day | A2-4 |
| 7. Inform the DNO | The installation document, signed by owner and installer | A3-1 or A3-2 |
| 8. Ongoing responsibilities | Any modification affecting technical capability must be reported, and may trigger retesting | — |
| 9. Decommissioning | Permanent removal must be notified | D0 |
Stages 8 and 9 are the ones that get forgotten. The obligation does not end when the scaffolding comes down.
Choosing the form
This is the decision your installer makes silently, and it is worth understanding because it determines whether you wait.
| Situation | Form | Wait before installing? |
|---|---|---|
| Aggregate capacity ≤16 A per phase, fully type tested | G98, not G99 | No — notify within 28 days |
| Small generation installation procedure SGI-1 | A1-2 | No — install, commission, then notify |
| SGI-2 or SGI-3 | A1-2 | Yes |
| Under 50 kW three-phase or 17 kW single-phase | A1-1 | Yes |
| Output shared with two or more customers, under 50 kW | A1-3 | Yes |
| Over 50 kW three-phase | Your DNO’s standard application form | Yes |
Two different numbers do two different jobs and they are easy to confuse.
16 A per phase — 3.68 kW single-phase is the boundary between the G98 process and the G99 process.
17 kW single-phase, or 50 kW three-phase is the boundary inside G99 between the simplified application form and your DNO’s full standard form.
A 6 kWp domestic system is above the first and well below the second: G99, simplified form.
Check the Type Test Register first
Before anything else, find out whether your inverter is fully type tested. If it is, the application quotes the manufacturer’s product ID and you avoid submitting full compliance evidence — G99 says the application “should include the Manufacturer’s reference number (the Product ID)” where the module is registered.
The register is public and free at connect-direct.energynetworks.org.
If the equipment is not type tested, a compliance verification report has to accompany the application, or you use the standard application form instead. That is a materially heavier process, and it is a fair question to put to an installer proposing unfamiliar equipment: is this on the Type Test Register?
What you will be asked for
Form A1-1’s fields, in substance. Worth gathering before you start rather than halfway through.
About you, the generator
- Name, address and postcode of the generator
- A contact person, if different
- Telephone and email
- Your MPAN — the supply number, on your electricity bill
About the installer
- Company name and address
- Accreditation or qualification
- Contact person, telephone and email
About the installation
- Site address, postcode and MPAN, where different from yours
About the equipment — for both existing and proposed units
- Manufacturer and approximate date of installation
- Energy source and conversion technology, entered as codes from the tables in the form
- Manufacturer’s reference number where available
- Registered capacity in kW, split by phase for single-phase units, and power factor
The requirement to declare existing generating units is the one people miss. If you already have solar and are adding a battery, or adding to an array, the application covers the whole installation and not just the new part.
The timescales that are actually guaranteed
Only the simplified procedures carry a commitment, and it is worth knowing which one you are in.
SGI-2 — the DNO “will provide the results of the assessment within 10 working days” of receiving the application.
SGI-3 — the DNO “will confirm within 10 working days” whether site-specific analysis is needed. That is a narrower promise: it is a commitment to tell you whether more work is required, not to finish it.
Both — your planned commissioning date on the form must be “between 10 working days and 3 months from the date that the application is submitted”.
Standard applications carry no equivalent guarantee in G99 itself, and a connection offer, once made, is valid for 3 months.
That last point matters more than it looks. Two of G99’s dates work against each other: your planned commissioning date cannot be more than 3 months ahead, and an offer expires after 3 months. On a project with any slippage, an application submitted too early can go stale.
At commissioning
Whether the DNO witnesses commissioning is its decision, and it tells you as part of the application assessment or the connection offer.
- Not witnessed: the site compliance and commissioning forms go in within 28 days.
- Witnessed: the forms can be signed and submitted on the day.
Then the installation document — signed by the owner and the installer, with declarations from the generator or their technical representative, and from the DNO’s witness where one attended. One form per power generating facility.
Ask for a copy. It is the record that the connection exists and was done properly, and it is the document a future buyer’s conveyancer may want to see.
Afterwards
Modifications. If you change the system in a way that affects its technical capabilities or its compliance, you must inform the DNO, who “may require compliance tests”. Adding a battery, changing an inverter, or lifting an export limit all plausibly qualify.
Decommissioning. Permanent removal is notified separately, at stage 9. As with G98, the obligation runs both ways: the operator’s model of what is connected to your street is only as good as the notifications it receives.
If it goes wrong
The DNO can refuse. G99 is explicit that it “shall refuse to allow the connection of a Power Generating Module which does not comply with the requirements and connection process set out in this EREC G99”, absent a derogation from the Authority.
It can also come back asking for network reinforcement, potentially at your cost. Both outcomes, and what you can do about them, are on what happens if your DNO refuses.
Sources
- Engineering Recommendation G99, issue 2 (10 March 2025) Free to download. ENA's own engineering database requires registration.
- Engineering Recommendation G98, issue 2 (10 March 2025) Free to download.
- ENA Type Test Register (Connect Direct)
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