Warning What does this mean?

Your system is down or running degraded, but this is not an immediate safety danger. Work through the safe steps below.

Sungrow Inverter Codes 004 and 005 — Grid Undervoltage Explained

Codes 004 and 005 both mean grid undervoltage — the AC voltage from the utility has dropped below the inverter's protection threshold. They are two stages of the same protection: 004 is stage I (voltage below the protective value) and 005 is stage II (voltage below an even lower value, beneath the 004 threshold). The inverter disconnects to protect itself and reconnects automatically when the grid recovers. Occasional dips are normal; frequent ones mean the supply or your AC cabling needs professional attention.

What should I do first?

Two quick questions — we'll point you to the right starting point.

Is this code still showing on your inverter's display?

What this code means

Voltage sags are one of the most ordinary events on any power grid — a large motor starting nearby, a fault on a distribution feeder, or heavy evening demand can drag local voltage down for seconds or minutes. Sungrow's inverters watch for this with a two-stage undervoltage protection, and the two codes tell you how deep the sag went. Code 004, "Grid undervoltage," means the voltage fell below the first protective threshold. Code 005, also "Grid undervoltage," means it fell further — below a second, lower threshold beneath the 004 value. Think of 004 as the amber stage and 005 as the red stage of the same event.

The inverter's response to both is identical and automatic: stop feeding power into a grid that is outside its allowed window, wait, and reconnect once the voltage has been back inside the window long enough to prove it is stable. Sungrow's manuals describe 005 explicitly as "a short-term fault due to grid condition" and advise simply waiting for inverter recovery. There is no damage implied by either code — they are the protection working as designed. What the codes cannot tell you on their own is whether the sag came from the utility's network or from your own installation (a long, thin, or poorly terminated AC cable dropping voltage under load). That distinction is the whole diagnostic question, and the pattern of occurrences answers it.

What is this downtime costing you?

Rough estimate while your system isn't producing. Adjust the numbers to match your setup.

System size (kW) Peak sun hours / day Electricity rate ($/kWh)

–per day

–per week

–per 30 days

≈ – kWh of lost production per day.

Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.

Common causes

Utility-side voltage sags: network faults, switching operations, or heavy regional demand dragging the local supply down temporarily.
An undersized or overly long AC cable between the inverter and the switchboard, which drops significant voltage when the inverter is exporting at full power.
A loose or corroded AC terminal or breaker in the switchboard increasing resistance on the inverter's feed.
Heavy loads elsewhere in the building pulling the local voltage down, especially where the inverter shares a long submain.
Scheduled grid maintenance or brownout conditions in areas with strained distribution infrastructure.

Safe steps to try

Work top to bottom, ticking off each step as you complete it. 0 of 5 done.

Check whether neighbors are affected or whether lights elsewhere in the house are dimming — a street-wide or house-wide dip points at the utility supply, while an inverter-only event points at your AC cabling.
Look at the timing: 004/005 appearing daily at full midday export suggests voltage drop in your own AC cable under load; random timing suggests utility-side sags.
Make sure the inverter's external AC isolator is fully switched on. Do not open the switchboard or touch any terminals.
In the monitoring app, check the logged grid voltage around the fault times — readings stuck near the lower protection limit during export point to a cable-sizing issue for your installer.
For 005 specifically, Sungrow's guidance is to wait for automatic recovery first; only investigate further if it recurs.

Is your inverter still under warranty?

Before paying for a repair, check — your installer may fix this free.

Brand Year installed

Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.

When to call an electrician

Call in professional help when the codes appear frequently — several times a week or daily — or when you are losing meaningful generation. If the dips affect the whole street or coincide with known network issues, the call goes to your local utility or grid operator. If it is only your inverter, your installer needs to check the AC cable: its cross-section, its length, and the quality of every termination from the inverter to the switchboard. Sungrow's manual says exactly this for 004: measure the actual grid voltage and contact the utility if it is out of range, check that protection parameters are set correctly, and verify the AC cable is firmly in place. Adjusting protection thresholds is installer-only and must stay within the local grid code.

Frequently asked questions

What is the difference between code 004 and code 005?

Both are grid undervoltage. 004 is stage I: the voltage dropped below the first protective threshold. 005 is stage II: the voltage dropped below a second, lower threshold beneath the 004 value. A 005 event is simply a deeper sag than a 004 event.

Will the inverter reconnect by itself?

Yes. Both codes are self-clearing: the inverter waits for the grid voltage to return inside the allowed window and stay there, then resumes feeding in automatically. No reset is needed.

Can undervoltage damage my inverter or appliances?

No — that is precisely what the protection prevents. By disconnecting during the sag, the inverter avoids operating outside its design window. Your appliances are on the grid side and unaffected by the inverter's decision.

Why does it happen at midday when the sun is strongest?

That pattern usually means voltage drop in your own AC cable: at full export power, an undersized or long cable loses significant voltage between the inverter and the switchboard. An installer can verify this with measurements.

Should I ask for the undervoltage threshold to be lowered?

Only your installer can change protection parameters, and only within what the local grid code allows. Lowering thresholds to hide a real cable or supply problem is the wrong fix — find the cause first.

Need a professional?

This fault may need professional diagnosis. Contact a qualified solar electrician in your area.

Sources: meaning and troubleshooting verified against the manufacturer's documentation — Sungrow SG2K-S to SG8K-D User Manual, Section 9 'Troubleshooting and Maintenance' — Code 004 'Grid undervoltage: the grid voltage is below the protective value (stage I)'; Code 005 'Grid undervoltage: the grid voltage is below the protective value, which is lower than the protective value of error 004 (stage II)'. Confirmed in Sungrow Distribution Europe Academy, Service FAQ: 'Fault codes 004, 005: Grid Undervoltage.'