F23 Fault Code Sunsynk and Deye: Tz_GFCI_OC_Fault Diagnostic and Fix Guide

Key Takeaways

• Fault code F23—labeled Tz_GFCI_OC_Fault on Sunsynk and Deye hybrid inverters—indicates that the control processor detected either an excessive transient current spike or AC leakage to earth.
• The alarm most frequently triggers at dawn when solar PV production commences, especially on installations configured with Low Power Mode enabled.
• During morning startup, the inverter transitions from standby to active grid synchronization, briefly drawing or outputting elevated currents that can trip sensitive internal ground-fault thresholds.
• Resolving persistent F23 alarms requires a systematic engineering approach: installing dual-side Type II Surge Protection Devices (SPDs), verifying grounding integrity, checking cable sizing, installing line reactors or LC filters, and updating inverter control firmware.
• If the alarm appears alongside physical breaker trips on downstream distribution boards, installers must isolate sub-circuits to rule out external appliance earth leakage.

Understanding the F23 Tz_GFCI_OC_Fault Mechanism

Sunsynk and Ningbo Deye hybrid inverters share a common power electronic architecture. Inside the inverter chassis, high-speed current sensors continuously monitor the balance between phase, neutral, and earth conductors, as well as the differential DC ground current from the photovoltaic array.

The manufacturer's technical engineering advisory defines the fault condition:

"F23 Tz_GFCI_OC_Fault occurs when either a transient current or AC leakage is detected. When the inverter starts-up each day there may be brief surges or spikes as the system stabilizes. During startup, the inverter might briefly draw or output more current than normal as it synchronizes with the grid or connected loads."

When the measured transient current or leakage exceeds factory safety thresholds, the inverter immediately opens its internal output relays and enters a protective shutdown state. This prevents thermal destruction of the inverter's insulated-gate bipolar transistors (IGBTs) and eliminates electric shock hazards on connected circuits.

Why F23 Triggers in Low Power Mode

A common scenario reported by South African installers occurs on systems utilizing the Low Power Mode setting:

"When using Low Power Mode, you might receive a fault code F23 during start-up of the inverter as PV production commences."

In Low Power Mode, the inverter powers down non-essential internal control circuits overnight to minimize battery parasitic consumption. When the first rays of morning sunlight strike the PV modules and string voltage crosses the startup threshold:

1. The inverter processor awakens and initializes the DC-to-DC boost stages.
2. The internal control loops attempt to synchronize AC frequency and phase angle with the municipal grid or home backup subboard.
3. If connected inductive loads (such as refrigerators, freezer compressors, or standby transformers) are energized simultaneously, the resulting inrush demand combines with the startup transient.
4. The rapid rate-of-change of current causes a brief ground-fault sensor trip, locking the inverter out on F23.

Review our companion guide on /za/guides/fixes/sunsynk-low-power-and-low-noise-mode for deeper context on configuring idle sleep settings.

Step-by-Step Diagnostic and Resolution Workflow

To eliminate recurring F23 trips, follow the manufacturer-recommended six-step mitigation procedure:

Step 1: Install Dual-Side Surge Protection Devices (SPDs)

Voltage spikes and high-frequency switching noise on utility lines or PV strings can distort current waveforms during startup.

• Purpose: "SPDs protect against voltage spikes and transient currents caused by lightning strikes, switching operations, or other disturbances."
• 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."
• Standard Ratings: While Deye and Sunsynk inverters integrate internal Type II surge suppressors, external DIN-rail Type II SPDs in the combiner box and AC distribution board provide sacrificial isolation against severe South African grid switching events.

Step 2: Install an AC Line Reactor (Inductor)

If the electrical environment suffers from severe inductive switching noise:

• 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."
• Placement: "Line reactors should be installed between the inverter and the AC load (or grid connection)."
• Effect: The added inductance acts as an electrical shock absorber, dampening rapid current spikes before they reach the inverter's internal measurement shunts.

Step 3: Install an LC or LCL Output Filter

For installations operating sensitive electronic loads or long AC cable runs:

• Purpose: "Filters are used to eliminate high-frequency components, which are often associated with transient currents."
• Placement: "Install an LC or LCL filter on the output side of the inverter (AC side) to reduce ripple and smooth out transients."

Step 4: Audit and Verify the Grounding System

Improper or high-resistance grounding prevents the dissipation of capacitive leakage currents from solar module frames:

• Purpose: "A proper grounding system reduces the impact of electrical transients and ensures that the inverter operates safely."
• Action: "Ensure your inverter and solar panel system are correctly grounded."
• South African Compliance: National wiring regulations require that all solar panel mounting rails, inverter chassis, and AC/DC surge protection devices bond directly to the main earthing terminal (MET). In TN-S and TN-C-S networks, verify that earth loop impedance is within standard limits to ensure transient dissipation.

Step 5: Upgrade Cabling and Connections

Undersized or loose electrical wiring increases circuit resistance and creates harmonic distortion:

• Purpose: "Poor-quality or undersized cables can introduce more noise and transients into the system."
• Action: "Ensure all cables, especially between the solar panels, inverters, and grid connections, are of high quality and appropriate sizing."
• Inspect all MC4 connectors, DC isolator screw terminals, and AC terminal blocks with a calibrated torque screwdriver to eliminate resistive hot spots.

Step 6: Update Inverter Firmware

Manufacturer firmware engineers continuously refine digital control algorithms:

• Purpose: "Inverter firmware often contains improvements to handle transient conditions more effectively."
• Action: Ensure your inverter's control software is up to date to benefit from improved startup ramping algorithms that reduce transient susceptibility.

Consult our walkthrough on /za/guides/fixes/sunsynk-firmware-update for instructions on flashing firmware via the mobile monitoring portal.

Distinguishing Internal Inverter Faults from External Earth Leakage

When troubleshooting F23, technicians must distinguish between an internal inverter malfunction and genuine earth leakage on household appliance circuits:

For deeper guidance on resolving residual current trips, review our guide on /za/guides/fixes/sunsynk-rcd-nuisance-tripping.

Conclusion: Eliminating Morning Startup Trips

An F23 fault code is not a death sentence for your Sunsynk or Deye inverter. By recognizing that the alarm reflects sensitive transient current and leakage detection:

• Ensure proper earthing continuity between the inverter chassis, PV frames, and main earth bar.
• Verify that Type II DC and AC surge arresters are installed and functional.
• Check that cable terminations are torqued correctly and sized to handle rated inrush currents.
• Update control firmware to take advantage of refined startup algorithms.