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G98 or G99: which one does your project need?

By Saqib Shah · · 9 min read

G99 types and connection stagesFour generator types A to D by size, above six connection stages from information to final notification, with the compliance checking stage highlighted as an iterative step. G99 at a glanceFour types by size and connection voltage, then one path from first enquiry to final notificationType A0.8 kW to under 1 MWbelow 110 kVType B1 MW to under 10 MWbelow 110 kVType C10 MW to under 50 MWbelow 110 kVType D50 MW and over, or110 kV and aboveThe path1Information2Applicationform3Offer andacceptance4Compliancechecking5Build andcommission6FinalnotificationStep 4 is a loop: you send evidence, the network operator reviews it, and you repeat until it is agreed.Types as defined in G99 and published by network operators. Check the current issue.

In short. Use G98 if the total generation at the connection is 16 A per phase or less (3.68 kW single-phase, 11.04 kW three-phase) and the equipment is fully type tested. You install it, then notify the network operator. Use G99 for anything bigger: for most G99 connections you apply first, get an offer, then prove compliance before you run in parallel. Getting it approved first time comes down to a complete form, drawings that agree with each other, and honest data.

What is the difference between G98 and G99?

Size, and who goes first. G98 is the Energy Networks Association (ENA) engineering recommendation for fully type tested micro-generators, “up to and including 16 A per phase”, on public low voltage networks. For anything above 16 A per phase, G98 itself says the G99 procedures apply.

Under G98 you normally install and commission, and the installer tells the network operator afterwards, no later than 28 days after commissioning (counting the day of commissioning). For most G99 connections the order is reversed. Small type tested installations up to 32 A per unit can use the faster G99 fast-track application; check your DNO. Apply first and wait for your DNO’s confirmation before connecting. You apply, the network operator makes an offer, you accept it, and only then do you build, test and get permission to operate in parallel.

What do the G98 limits actually mean?

The limit is a current, not a kilowatt figure. G98 turns 16 A per phase into 3.68 kW on a single-phase supply and 11.04 kW on a three-phase supply, at a nominal 230 V. G98 takes the capacity as the lesser of the inverter rating and the rating of the energy source.

Two details catch people out. The limit applies to the installation, not to each box: if extra generation takes the total above 16 A per phase, G98 says the G99 process applies and the network operator needs to be consulted before the installation. And electricity storage counts, because G98 defines micro-generators to include storage devices.

How are G99 types A to D defined?

By the capacity of the power generating module and the voltage at the connection point. G99 Issue 2 defines them (the ENA application form repeats them):

  • Type A: connection point below 110 kV, 0.8 kW or greater but less than 1 MW.
  • Type B: below 110 kV, 1 MW or greater but less than 10 MW.
  • Type C: below 110 kV, 10 MW or greater but less than 50 MW.
  • Type D: connection point at 110 kV or above, or below 110 kV with 50 MW or greater.

The unit that counts is the module, not the site. G99 gives examples: three synchronous 400 kW units are three separate Type A modules, while units connected through power electronics or asynchronous machines at one connection point form one Power Park Module, so 1.2 MW of them is one Type B module. Ask your network operator how your scheme will be classified before you design around a type.

The type sets the weight of the evidence. Types B, C and D keep a Power Generating Module Document, completed as the project progresses and finalised before the network operator issues a Final Operational Notification. The ENA form also says that a module above 16 A per phase but under 17 kW (or under 50 kW three-phase) will “probably” be able to use the shorter form, which G99 Issue 2 calls Form A1-1.

What is the route to an approved G99 application?

  1. Apply on the ENA standard application form. Parts 1 to 4 are the minimum at initial submission.
  2. Receive the offer and accept it. G99 does not change the statutory timescales for quotations.
  3. Agree the compliance evidence. At Electricity North West, a “Compliance Submission Programme” lists each technical criterion and how you will prove it: site test, type test or simulation. You then submit studies, evidence and the module document, and the network operator reviews them. It calls this an iterative process.
  4. Witness testing, then the Final Operational Notification (for Types B to D; a Type A module ends with an installation document). Apart from compliance testing and commissioning, you have no permanent right to operate in parallel until it is issued.

Plan for step 3 as a loop, not a single submission. G99 asks for the module document at least 28 days before first synchronisation, or a shorter period the network operator accepts, and for 28 days’ notice of witnessed tests. Electricity North West encourages sending it early.

How do you get it approved first time?

Treat the form as a statement of how ready the project is. The ENA form says generators “should have sufficiently developed their plans to at least an outline level of detail”, and that failing to provide the information “will result in delays to the DNO providing a connection offer”.

Alex, an engineer at a small consultancy, is preparing an application for 1.2 MW of inverter-connected solar at an 11 kV connection for a farm client. Alex knows this is far above the G98 limit, and that inverter-connected solar at one connection point is one Power Park Module, so 1.2 MW makes it Type B if that is the inverter (AC) rating rather than the panels’ DC rating. At 1 MW or more the form also asks for a letter of authority, heads of terms and a timeline (see the list below). So Alex asks about classification before drawing anything.

What should you have ready before you submit?

  • The right form: the full ENA form for every Type A module over 50 kW and all Type B, C and D modules.
  • Contact details, a site boundary plan (the form asks for a red line boundary at 1:500), your preferred connection point voltage, a site layout plan and a detailed engineering design plan.
  • At 1 MW or more of new generation, unless the network operator names a lower threshold: letter of authority, heads of terms and preliminary project timeline.
  • A single line diagram that matches the data in Parts 3 and 4. The form says discrepancies “will cause delays in processing the application or for it to be rejected”.
  • A diagram of the interface arrangements: how the generator connects, disconnects and synchronises. The form says leaving it out will delay the application.
  • Import and export figures, firm and non-firm. Include the site’s import for any load, not only the export.
  • Fault current contribution, with where and at what voltage it was estimated.
  • Part 4 data for each different type of generating unit. If you have no equipment yet, use a proposed supplier’s data, mark what is estimated, and confirm it before commissioning.
  • Existing MPANs and connection agreements at or near the connection point.
  • Budget estimate or formal quote, and the type test references: G99 says an application for fully type tested Type A equipment should include the manufacturer’s reference number on the ENA Type Test Register (for larger types, the references of type tested components such as inverters and interface protection).

What do network operators check, and why do they raise queries?

For G98 they check the type test evidence. Electricity North West says it checks the validity of the type test information after you notify. SSEN says the power rating on the inverter certificate must match the inverter rating on the schematic. For G99 the published triggers are the ones above: missing data, a single line diagram that disagrees with the data tables, and a missing interface diagram. Another is existing protection. Electricity North West says it does not let a G99 generator sit behind a G59 compliant protection interface, so you either upgrade the interface or apply for a new point of connection. That is its own policy; G99 itself shows G59 and G99 modules in one installation. We found no published list of the most common queries, so ask your network operator which parts it reviews first.

Frequently asked questions

Does a battery need G99?

Not necessarily. G98 treats electricity storage as a micro-generator, so storage within the 16 A per phase limit, counting everything already on the installation, can use G98. Above that it is a G99 matter. Storage commissioned since 1 September 2022 has to meet G98 in full; the exclusions in its Appendix 1 apply only to older installations.

Do I need approval before installing under G98?

Usually you install and then notify. SSEN lists cases where you must apply first, including more than one generator at a single property, or total generation above the G98 limits. Several installations in a close geographic area use G98’s own Form A, and connect only once the network operator approves.

Can I submit estimated data?

Yes, at initial submission, if you say it is estimated. The ENA form says initial data can be estimated values and that complete Type A data must be provided before synchronising.

When can I switch on a Type B, C or D generator?

When the network operator issues the Final Operational Notification (for Type D, after an energisation and an interim notification first). Before then G99 allows parallel operation only for compliance testing and commissioning.

This is orientation, not advice. Read G98 or G99 itself and use your network operator’s current form and guidance.

Sources

Checked against these sources on 23 October 2026.

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