Deye F42: AC Line Low Voltage
F42 means the grid voltage the inverter sees has fallen below the allowed range, so it disconnects to protect itself and the grid. This is usually a grid-side event like a brownout or a weak supply, and the inverter reconnects on its own once voltage is back to normal.
Is it the grid, your wiring, or the inverter?
- A brownout or weak grid. The utility voltage genuinely sagged. Most common, and it self-corrects.
- Voltage drop on a long or thin AC cable between the inverter and the connection point, which can pull the reading low under load.
- A loose AC connection adding resistance.
- Standard limits: the inverter follows grid-protection rules, so it trips even on dips that your appliances might tolerate.
The safe fix, step by step
- Wait for it to clear. If the grid voltage was just low for a while, F42 clears by itself when it recovers. A brief, occasional F42 is normal on weaker grids.
- Notice how often it happens. Rare and brief is fine. Frequent or long F42 events point to a genuinely weak supply or a wiring issue.
- Check for obvious causes. If your whole area has low or unstable power, it's the utility. If only your system reads low, the AC cabling may be the cause.
- For persistent F42, call your installer to check the AC cable sizing and connections, or contact your utility about supply voltage.
Quick decision flowchart
F42 appears
↓ is it rare and brief, clearing on its own?
✅ Yes → normal grid dip. Nothing to do.
❌ Frequent or long-lasting → weak supply or AC wiring issue.
↓
Persistent F42: installer checks AC cable sizing and connections; utility checks supply voltage.
Related Deye codes
FAQ
My appliances work fine, so why does the inverter complain?
Grid-tied inverters must follow strict voltage limits set by standards, tighter than what household appliances tolerate. So the inverter can trip on a dip your lights barely notice.
F42 happens a lot in the evening. Why?
Evening demand can pull neighborhood voltage down. If it's frequent, mention it to your installer and utility, since a chronically low supply isn't ideal for the system.
Sources
- Deye Hybrid Inverter User Manual (F42 = "AC line low voltage"; check the AC voltage is within the standard range).
- Deye dealer technical references for grid-voltage codes.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". This guide covers observation only. AC cabling and connection checks must be done by a licensed installer or electrician.