G99 vs G98: When Do You Need G99 Instead of G98?
Updated August 2026. G98 and G99are the two main UK connection routes for small solar generation. The dividing line is normally 16 A per phase, which is 3.68 kW on a single-phase home supply. Under that line you usually notify after installation under G98. Over that line you apply first under G99.
3.68kW
Single-phase G98 threshold
16A
Limit per phase
28 days
G98 notification window
Before
G99 approval timing
The 3.68kW threshold in plain English
The practical dividing line is 16 A per phase. On a standard UK single-phase domestic supply, that is usually expressed as 3.68 kW. A generator at or below that size can normally use G98, provided the equipment is type tested and the installation meets the wiring rules. A generator above that size normally falls under G99.
The difference is more than paperwork timing. G98 tells your DNO (your electricity network operator) what has already been connected. G99 asks the network to assess the connection before it is energised. The network may need to check local cables, transformers, voltage rise, export limits, fault levels, and protection settings.
G99 approval comes before connection
G98 vs G99 comparison table
| Topic | G98 | G99 |
|---|---|---|
| Typical size | Up to 16 A per phase, normally 3.68 kW single-phase | Above 16 A per phase or more complex generation |
| Process | Notification after connection | Application and approval before connection |
| Timing | Send within 28 days after installation | Wait weeks or months before installation or energisation |
| Network decision | No prior approval for compliant small generation | Written approval or connection offer needed first |
| Fees | Usually no notification fee | Fees may apply, depending on the network and scheme |
| Homeowner examples | 800 W plug-in solar, small type-tested microgeneration | Larger rooftop solar, multiple inverters, three-phase systems |
Who needs G99?
G99 is common for larger rooftop solar systems, especially 3-6 kW+ domestic arrays where total generation exceeds the single-phase G98 limit. It may also apply when a property has multiple inverters, existing solar plus new solar, export-capable battery storage, or a three-phase supply. Commercial premises usually need a closer G99 assessment because capacity, load, phases, and export arrangements vary more widely.
A system does not become G98 just because one inverter is small. The relevant question is the total generation operating in parallel with the public network at the premises. If in doubt, use the DNO lookup to identify your DNO (your electricity network operator) and ask for the correct connection route before equipment is energised.
When plug-in solar will never need G99
A compliant plug-in solar kit is capped at 800 VAunder the plug-in solar route. That is far below 3.68 kW, so a homeowner using a single approved plug-in kit as supplied should not need G99. The normal route is a G98 notification within 28 days after the kit is connected.
The key condition is that the kit is used as the manufacturer intended. Do not combine kits, modify leads, add extra inverters, or connect extra panels beyond the approved design. Those changes can move the installation outside the plug-in product route and into ordinary electrical design and network connection rules. For wider context, read the plug-in solar UK guide and the guide to whether plug-in solar is legal.
What happens if you exceed G98 limits without G99 approval?
Connecting a G99-scale system without approval can breach the Electricity Safety, Quality and Continuity Regulations (ESQCR) and the network connection rules. Your DNO (your electricity network operator) can require changes, refuse export, or disconnect unsafe or unauthorised generation.
Approval protects the local network
What to do next
- For a plug-in solar kit, use the G98 readiness checklist.
- When you have the details, create the G98 notification form.
- For a larger system, identify your network with the DNO lookup and ask about G99 before installation.