18x1C on a SolarEdge HD-Wave single-phase inverter: AC Voltage Too Low: Line voltage is low
Short answer
On a SolarEdge inverter, 18x1C means: AC Voltage Too Low: Line voltage is low. The inverter stops until the fault clears or is reset.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: AC Voltage Too Low: Line voltage is low.
Part involved: AC grid protection (under-voltage).
Likely causes:
- Low grid voltage.
- Wrong country setting.
- Loose AC connection.
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 grid voltage returns within limits.
Manual reset: no.
What you can check
- Read and note the exact code and time from the inverter display or app (screenshot).
- Check the solar/battery AC isolator and the consumer-unit breaker/RCD are ON (do not reset a breaker that trips again immediately).
- Check whether there was a local power cut or dip at the time.
- 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
- Measure supply voltage.
- Check AC terminations and neutral integrity.
- Confirm UK country setting.
- Refer to DNO if supply is low.
Who to ask for: PV installer / electrician; DNO.
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.15 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026