Sunsynk Error F23: GFCI Leakage Overcurrent and RCD Tripping Resolution Guide

Key Takeaways

• Sunsynk error F23 indicates that the internal Ground Fault Circuit Interrupter (GFCI) detected an AC leakage current or an abrupt transient current surge.
• Morning nuisance trips frequently stem from transient grid synchronisation surges coinciding with moisture condensation across rooftop solar array frames and connector plugs.
• Always isolate all power feeds before examining external cabling, ensuring complete circuit de-energisation to eliminate shock hazards.
• Hardware solutions for persistent transient trips include installing surge protection devices (SPDs), adding an inductive line reactor to smooth waveforms, or fitting an LC or LCL harmonic filter.
• Proper grounding across the solar arrays and inverter chassis facilitates safe transient dissipation and eliminates ground reference drift.

What is Sunsynk error F23?

Modern transformerless solar inverters maintain sensitive current sensors that continuously calculate the algebraic sum of live and neutral currents. On Sunsynk hybrid inverters, when this differential current exceeds internal protection thresholds, the unit trips with fault code F23, officially designated as an AC leakage current transient overcurrent fault.

Sunsynk engineering guidance establishes that this alert: "occurs when either a transient current or AC leakage is detected."

When F23 triggers, the inverter instantly decouples from the distribution network to eliminate potential shock risks or equipment damage. For British homeowners and system operators, this often coincides with the tripping of an upstream residual current device (RCD) located within the domestic consumer unit or solar distribution board.

Understanding the root cause requires evaluating both photovoltaic array ground leakage and alternating current distribution dynamics. For complete details on electrical earthing and safety standards in the United Kingdom, consult our UK solar electrical installation guide.

Morning startup surges and transient leakage

A widespread operational symptom reported by UK system owners is that error F23 trips predominantly during early morning hours as the solar array first catches daylight.

Sunsynk technical support clarifies why startup creates heightened vulnerability: "During startup, the inverter might briefly draw or output more current than normal as it synchronizes with the grid or connected loads."

This brief inrush occurs simultaneously with natural environmental phenomena:

1. Capacitive Moisture Coupling: Overnight dew, fog, or rainfall leaves a thin moisture film across solar glass and aluminium module frames. This creates a distributed capacitive leakage path between the photovoltaic cells and earth.
2. Synchronisation Inrush: As the inverter switches on its semiconductor bridge to match the mains utility waveform, the sudden voltage transition charges this parasitic capacitance, producing a momentary spike in earth leakage.
3. Trip Point Activation: If the combined transient spike exceeds the inverter GFCI window, error F23 posts immediately, and the inverter restarts its connection countdown.

Once ambient sunlight and warmth evaporate the surface moisture, insulation resistance naturally rises, allowing the inverter to synchronize normally without further tripping.

Hardware triage: DC cabling and module earth shorts

When F23 persists during dry daylight conditions, the fault indicates a physical breakdown in circuit insulation rather than a benign atmospheric transient.

Sunsynk documentation sets out the baseline troubleshooting checklist: "F23 AC leakage current is trans over current Leakage current fault 1.Check the PV module and inverter cables. 2.You may have a faulty PV panel (earth short) 3.Restart inverter"

Triage Sequence for Installers

1. Inspect DC Cable Runs: Check DC string cabling along roof tile edges and entry flashings for chafing against metallic slate hooks or structural roof brackets.
2. Examine Rooftop Connectors: Verify that all string connectors are fully mated, correctly crimped, and held off roof valleys where water can pool.
3. Conduct Insulation Resistance Testing: Using an insulation resistance tester under disconnected conditions, measure resistance between positive to earth and negative to earth. A reading below required thresholds confirms an earth short.
4. Isolate Individual Strings: On systems with dual string inputs, disconnect one string at a time to identify which array branch houses the defective module or pinched conductor.

Requirements for microgenerator connection and protection are further detailed in our micro-generator grid connection guide.

Suppressing transient currents: reactors, SPDs, and filters

Where solar array insulation tests prove sound but transient electrical disturbances from switching or the local network continue to trip F23, Sunsynk technical documentation recommends coordinated engineering mitigations:

1. Surge Protection Devices (SPDs)

Electrical switching transients from nearby heavy equipment or atmospheric disturbances can destabilize inverter current tracking: "Purpose: SPDs protect against voltage spikes and transient currents caused by lightning strikes, switching operations or other disturbances."

Proper placement ensures comprehensive protection across all system ports: "Placement: Install SPDs on both the DC side (solar panel to inverter) and the AC side (inverter to load/grid). Make sure the SPD is rated appropriately for your system."

2. Inductive Line Reactors

In areas with high supply impedance or rapid load stepping, introducing series inductance stabilizes current flow: "Purpose: A line reactor helps filter out transient currents by adding impedance to the circuit, which smooths out the current flow and limits rapid changes in current."

Proper physical placement is vital for attenuating steep di/dt transitions: "Placement: Line reactors should be installed between the inverter and the AC load (or grid connection)."

3. Harmonic Output Filters

Where complex multi-inverter setups or non-linear loads introduce severe waveform ripple, Sunsynk technical support advises: "Placement: Install an LC or LCL filter on the output side of the inverter (AC side) to reduce ripple and smooth out transients."

These low-pass filter networks trap high-frequency carrier ripple and smooth harmonic content, preventing false GFCI trips.

4. Grounding System Integrity

Protective earthing plays an active role in dissipating high-frequency noise and stabilizing common-mode voltages: "Action: Ensure your inverter and solar panel system are correctly grounded. This can also help in dissipating any transient currents."

5. Low Noise Mode Configuration

In the inverter software settings, installers can also engage electromagnetic compatibility mitigation: "Low Noise Mode: Low noise mode is used to prevent potential interference with other electrical components on site."

Larger three-phase installations should also ensure alignment with our commercial grid connection guide.

Step-by-step diagnostic workflow

To systematically isolate an F23 error:

1. Observe Fault Timing: Determine if the code trips exclusively at dawn or continuously throughout the day.
2. Conduct Cold Inverter Restart: Isolate DC and AC isolators, wait several minutes, and re-energize to confirm whether the alert is latching.
3. Verify Array Insulation: Test photovoltaic strings with an insulation resistance meter under dry conditions.
4. Evaluate Upstream RCD Discrimination: Ensure consumer unit protective devices comply with inverter manufacturer leakage recommendations.

When to escalate to technical support

If external solar array cables, isolators, and junction boxes show no earth leakage, and transient suppression devices have been evaluated without resolving repeated F23 lockouts, escalate the incident to an MCS installer or Sunsynk engineering support.

Have the inverter serial number, installation date, and full display event log ready when opening a support case. Prompt triage ensures your system returns to clean generation, safeguarding your energy bill savings and export returns under our Smart Export Guarantee guide.