DNO Application Checker
Check if your installation needs a G98 notification or G99 application
Reference Info & Formulas
G98: Up to 16A/phase. Fit and notify — no wait.
G99: Above 16A/phase. Full application — await DNO approval.
Single phase: 3.68kW limit for G98
Three phase: 11.04kW limit for G98
MCS certification required for installer
Existing generation capacity counts toward limit
CT metering may be needed above 30kW
Data: ENA EREC G98 & G99
For guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.
How This Checker Works
This tool determines whether a generation installation requires a G98 notification or G99 application based on the system's capacity, phase configuration, and technology type.
The key threshold is 16A per phase, which equates to 3.68kW on a single-phase 230V supply (16 × 230 = 3,680W). Installations at or below this limit follow the simpler G98 notification route. Anything above — or any three-phase installation regardless of size — requires a full G99 application with DNO approval before commissioning.
Where multiple generation sources are present (e.g. solar PV plus battery storage), the total inverter capacity is aggregated. A 3kW solar inverter combined with a 3kW battery inverter totals 6kW, which exceeds the G98 threshold and requires a G99 application even though each inverter individually falls below the limit.
Quick Reference — G98 vs G99
ENA Engineering Recommendation comparison
ENA EREC G98 Issue 5, G99 Issue 7| G98 (Notification) | G99 (Application) | |
|---|---|---|
| Capacity limit | ≤16A per phase (≤3.68kW) | >16A per phase (>3.68kW) |
| Phase | Single phase only | Single or three phase |
| Process | Notify DNO, no approval needed | Apply and await written approval |
| Response time | None — install after notification | Up to 45 working days |
| Commissioning form | G98 notification form | G99 commissioning confirmation |
| CT metering | Not required | Required above 30kW (varies by DNO) |
| Export limiting | Not typically required | May be required by DNO |
Thresholds are based on total inverter capacity across all generation sources at the premises.
Quick Reference — Common Installation Scenarios
Typical generation installations and their DNO requirements
ENA EREC G98, G99| Installation | Typical Capacity | Route | Notes |
|---|---|---|---|
| Domestic solar PV | 3-4kW | G98 or G99 | G98 if ≤3.68kW; G99 if above |
| Solar PV + battery | 3kW + 3kW = 6kW | G99 | Aggregate capacity exceeds 3.68kW |
| Commercial solar PV | 10-50kW | G99 | CT metering likely above 30kW |
| Battery storage only | 3.6kW | G98 | If inverter capacity ≤3.68kW |
| Wind turbine | 1-6kW | G98 or G99 | Depends on rated output |
| Standby generator | Varies | G99 | If parallel operation with grid |
Standby generators operating in island mode (not exporting) may not require DNO notification, but always confirm with your DNO.
Practical Notes
Never Energise Before G99 Approval
Aggregate All Generation Sources
Submit G99 Applications Early
DNO-Specific Requirements Vary
Frequently Asked Questions
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