GoodWe Vac Failure: Grid Voltage Out of Range
Vac Failure (error 15) means the grid voltage your GoodWe measures has drifted outside the allowed range, so it disconnects to protect itself and the grid. It is one of the most common GoodWe messages, and it is usually a grid-side issue that clears on its own when the voltage settles.
Grid, your wiring, or a setting?
- AC cable voltage rise. As the inverter exports at full power, the voltage at its terminals climbs. A long or thin AC cable makes this worse. This is the classic cause of midday Vac Failure.
- A genuinely high or weak grid that sits near the edge of the allowed band.
- A voltage-protection setting narrower than your local grid actually runs.
How to handle it
- Wait for it to clear. A brief, occasional Vac Failure when the grid swings is normal; the inverter reconnects automatically.
- Notice the pattern. If it happens mostly at midday under full sun, that points strongly to AC cable voltage rise rather than a passing grid event.
- Have the AC cable checked. A loose or undersized AC cable raises the voltage the inverter sees. Shortening the run or increasing the cable size is the real fix, and that is an installer job.
- The protection range can sometimes be adjusted by an installer within what your grid code allows. Don't change safety limits yourself.
Quick decision flowchart
Vac Failure appears
↓ is it rare and brief, clearing on its own?
✅ Yes → a normal grid swing. Nothing to do.
❌ Frequent, especially at midday → likely AC cable voltage rise or a weak grid.
↓
Persistent Vac Failure: installer checks the AC cabling and, if appropriate, the voltage range.
Related GoodWe codes
FAQ
My appliances work fine, so why Vac Failure?
Grid-tied inverters follow strict voltage limits set by the grid code, tighter than what household appliances tolerate. The inverter can trip on a swing your lights barely notice.
It only happens at midday when the sun is strongest.
That is the classic sign of AC cable voltage rise: as the inverter pushes maximum power out, the voltage at its terminals climbs above the limit. Have your installer check the AC cable size and connections.
Helpful guides
Sources
- GoodWe inverter user manual and error-message list (Vac Failure / error 15 = grid voltage outside the permitted range).
- GoodWe installer documentation.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". This guide covers observation only. AC cabling and protection-setting changes must be done by a licensed installer in line with your grid code.