18x40 on a SolarEdge HD-Wave single-phase inverter: AC Freq Too High: The frequency measured on L1 is higher than the thresholds
Short answer
On a SolarEdge inverter, 18x40 means: AC Freq Too High: The frequency measured on L1 is higher than the thresholds. The inverter stops until the fault clears or is reset.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: AC Freq Too High: The frequency measured on L1 is higher than the thresholds.
Part involved: AC grid protection (frequency).
Likely causes:
- Grid frequency outside G98/G99 limits.
- Wrong country setting.
Is it safe?
| Does the inverter stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
The inverter stops until the fault clears or is reset.
Resetting itself: yes - reconnects when frequency is back within limits.
Manual reset: no.
What you can check
- Read and note the exact code and time from the inverter display or app (screenshot).
- Usually a brief grid disturbance; no action if it clears the same day.
- Check the solar/battery AC isolator and the consumer-unit breaker/RCD are ON (do not reset a breaker that trips again immediately).
- If the code persists, contact the installer. SolarEdge's list says 'OFF/ON to reconnect' for some codes - that means the inverter's own ON/OFF switch; only use it if your installer has shown you how. Never open the inverter or touch DC cables/connectors.
What the engineer will check
- Verify country/grid code (UK G98/G99).
- Log grid frequency.
- Check for unstable supply (e.g. generator/backup operation).
Who to ask for: PV installer.
Certification: Usually none (grid-side event). If persistent: installer/electrician to measure supply voltage and check settings; DNO investigates supply voltage (G98/G99 protection settings must not be changed without DNO agreement).
What you might notice
Sources
- User Guide: SolarEdge Inverters Error Codes and Troubleshooting, Version 1.1 (January 2026) ↗ · 1.1 · page PDF p.20 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026