Problem diagnosis · Huawei

Huawei SUN2000 AFCI Fault — DC Arc Detection Alarm & Safe Reset

Your SUN2000 inverter has detected a possible DC arc fault and shut down as a safety precaution. A single trip may be a nuisance event — but repeated AFCI alarms indicate a real wiring issue that must be inspected before resetting. This guide explains what to check and when it is safe to clear the alarm.

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Written by Ronald · Independent Solar Engineer Last updated 28 October 2026

DC arc faults are a fire hazard. The AFCI system exists to detect arcing on DC solar panel wiring — the same type of fault that causes PV fires. If the alarm has triggered more than once, do not reset the inverter without inspecting the DC cabling first. If you see visible damage, smell burning, or notice discolouration around connectors, isolate the system at the consumer unit and call a qualified solar engineer.

Diagnostics

6-step AFCI fault diagnosis

A single AFCI trip can be cleared with a power cycle (step 3). Repeated trips require a DC cabling inspection (step 4) before the alarm is cleared (step 5). Never bypass AFCI protection.

Check the alarm in FusionSolar and note the details

Open the FusionSolar app and check the alarm log. Look for a DC arc fault alarm. Note the time it triggered and — if shown — which PV string was involved. Check how many times the alarm has appeared in the last 24 hours.

Single trip

Likely a nuisance event. A power cycle (step 3) is a reasonable first response. Monitor for recurrence.

Multiple trips or lockout

A persistent fault on the DC wiring. Do not attempt a power cycle — go directly to step 4 for cabling inspection.

Understand the 5-trip lockout mechanism

The SUN2000 has a built-in AFCI auto-clearance system:

Fewer than 5 trips in 24 hours: The inverter automatically clears the alarm and restarts. No manual intervention is required — but you should still investigate if it trips more than once.

5 or more trips in 24 hours: The inverter locks for protection and will not restart automatically. The alarm must be cleared manually via the FusionSolar app or portal (step 5). The DC cabling must be inspected first (step 4).

Each power cycle that results in another trip counts toward the lockout. Do not repeatedly restart the inverter to "get past" the alarm — this worsens the situation and accelerates the lockout.

For a single trip — power cycle and monitor

If the alarm has triggered only once, a power cycle is appropriate:

1. Turn off the AC isolator

2. Turn off the DC isolator on the inverter

3. Wait 5 minutes — longer than a normal restart to ensure full discharge

4. Turn DC isolator back on, then AC isolator

Monitor the system for the rest of the day. If the alarm does not return, it was likely a nuisance trip caused by moisture on a connector, a transient electrical disturbance, or environmental interference.

Alarm returned? Do not power cycle again. The fault is persistent — proceed to step 4 for DC cabling inspection.

Inspect DC cabling and MC4 connectors

Repeated AFCI trips indicate a genuine DC arc fault. The wiring between the solar panels and the inverter must be physically inspected. This should be carried out by a qualified solar engineer with DC-safe PPE and insulated tools. Common fault locations:

MC4 connectors: Loose, partially disconnected, corroded, or with water ingress. These are the most common cause of DC arc faults on domestic solar installations.

Cable insulation damage: Cables rubbing against sharp roof edges, mounting rails, or tile hooks. Wind movement causes gradual chafing that eventually exposes conductors.

Junction boxes: Water ingress or heat damage to the junction box on the back of a panel. Check for discolouration or melting.

DC isolator switch: Corroded or damaged internal contacts. Rooftop isolators are exposed to weather and degrade over time.

Rodent damage: Squirrels, pigeons, and other wildlife can damage cable sheathing under panels. Look for gnaw marks or nesting material around cables.

If the affected string is identified in FusionSolar, focus the inspection on that string first. If not, all strings need checking.

Clear the AFCI alarm via the FusionSolar app

Once the DC cabling has been inspected and any faults repaired, clear the alarm:

1. Open the FusionSolar app → tap Me → Device commissioning

2. Connect to the inverter — scan the QR code on the inverter or enter the serial number

3. Log in with the installer account (default password: 00000a)

4. Tap Alarm management

5. Find the DC arc fault alarm and tap Clear

The inverter will restart and resume generation. Alternatively, the alarm can be cleared via the FusionSolar web portal under Maintenance → Alarm Management using a non-owner account.

If you do not have installer-level FusionSolar access, your installer can clear the alarm remotely or you can book an STS remote diagnostic.

If the alarm returns after clearing — do not reset again

If the AFCI alarm triggers again after clearing, the DC fault has not been fully resolved. Repeated arcing at the same location increases the risk of fire. At this point:

• Do not continue to clear and restart the inverter

• The fault location needs to be identified using string-level voltage and current testing

• Every connector, cable run, junction box, and isolator on the affected string needs individual testing

• Thermal imaging can help locate hot spots at degraded connections

STS can narrow down the likely fault location remotely using FusionSolar string performance data and alarm patterns before an engineer attends site — reducing time and cost.

What AFCI is and why it matters

AFCI (Arc Fault Circuit Interrupter) is a safety feature built into Huawei SUN2000 inverters that detects dangerous DC arc faults on solar panel wiring. A DC arc occurs when a connection is poor enough that electricity jumps across a gap — like a spark inside a loose connector. Unlike AC arcs that are interrupted every time the voltage crosses zero, DC arcs are continuous and self-sustaining, generating extreme heat at the fault point. This is why DC arc faults on solar installations are a leading cause of rooftop fires.

The SUN2000's AFCI system analyses the electrical noise pattern on each PV string to distinguish genuine arcs from normal electrical variation. When it detects an arc signature, it shuts down the affected string immediately. The system is enabled by default and under MIS 3002:2025 it must remain enabled — this is a mandatory requirement for UK solar installations, not an optional feature. AFCI works with standard PV modules and Huawei optimisers but does not support third-party optimisers or smart modules.

Nuisance trips do occur — moisture, transient interference, and certain environmental conditions can produce electrical patterns that resemble an arc. A single nuisance trip that clears after a power cycle and does not recur is not a concern. But any alarm that returns should be treated as a genuine fault until proven otherwise. The consequences of ignoring a real arc fault are severe.

AFCI arc fault — common questions

What causes an AFCI fault on a Huawei SUN2000 inverter?

The AFCI system detects DC arc faults on the solar panel wiring. Common causes include loose or partially disconnected MC4 connectors, water ingress into connectors or junction boxes, chafed cable insulation where cables rub against mounting rails, rodent damage, and corroded DC isolator contacts. A single trip can be a nuisance event caused by transient noise or moisture — these typically clear after a power cycle and do not recur.

How do I clear an AFCI alarm on a Huawei SUN2000?

Open the FusionSolar app, go to Me → Device commissioning, connect to the inverter, and log in with the installer account (default password: 00000a). Tap Alarm management and tap Clear next to the DC arc fault alarm. You can also clear it via the FusionSolar web portal under Maintenance → Alarm Management. Do not clear the alarm without inspecting the DC cabling if it has triggered multiple times — see step 4 above.

Why does my Huawei inverter keep tripping on AFCI?

Repeated AFCI trips indicate a persistent DC arc fault. The most likely cause is a degraded MC4 connector — loose, corroded, or with water ingress. Every connector, cable run, and junction box on the affected string needs inspecting. Do not continue to reset without investigation, as repeated arcing at the same location is a fire hazard. The SUN2000 locks after five trips in 24 hours to enforce this.

Can I disable AFCI on a Huawei SUN2000 inverter?

AFCI is enabled by default and should not be disabled. Under MIS 3002:2025, arc fault detection must be enabled where the inverter supports it — this is mandatory, not optional. Disabling AFCI removes a critical fire safety protection. If nuisance trips are occurring, the correct approach is to fix the wiring issue causing the false detection, not to disable the protection.

What does the Huawei SUN2000 5-trip AFCI lockout mean?

If the AFCI alarm triggers five or more times within 24 hours, the SUN2000 locks and will not restart automatically. This safety mechanism prevents repeated arcing. The lockout can only be cleared manually via the FusionSolar app (Me → Device commissioning → Alarm management → Clear) or the web portal. The DC cabling must be inspected and repaired before clearing. If the alarm triggers fewer than five times in 24 hours, the inverter clears automatically.

What does it cost to sort a Huawei AFCI fault?

The remote diagnosis is free. We read your FusionSolar alarm history and per-string data to narrow the arc fault to a likely connector or cable before anyone climbs on the roof. Because an arc fault is physical it's an on-site repair — usually a single degraded MC4 connector — quoted first, from £295. The remote work that pinpoints it costs you nothing.

How quickly can you look at a Huawei AFCI alarm?

Usually the same day. We read your FusionSolar alarm log and per-string performance in a 30-minute remote session to point the engineer straight at the faulty string — you get a written summary of the likely cause and the safe next step straight after. For other codes, see the Huawei fault code index.

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AFCI alarm keeps returning?

Repeated arc fault trips need professional diagnosis. We can identify the likely fault location remotely using FusionSolar string performance data and alarm history — reducing the time and cost of an on-site visit. Most AFCI issues are traced to a single degraded connector.

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