Deye SUN-12K-SG04LP3 Error F18: GFCI Leakage Current Trip
Error F18 indicates that the residual current monitoring unit (RCMU/GFCI) detected an AC or DC leakage current to ground exceeding the safety limit (typically >30mA continuous or >300mA instantaneous spike), triggering an emergency disconnect from the grid.
Hardware Diagnostic Matrix
Spec Ref #ed7cbcc4Required Diagnostic Tools & Instrumentation
Multimeter Probing Targets & Circuit Tolerances
Bench Calibrated ±5%| Test Point / Circuit | Target Nominal Spec | Expected State | Fault Condition |
|---|---|---|---|
| Main Logic DC Bus | 3.3V / 5.0V DC (±0.1V) | Stable DC Potential | <2.9V (Brownout / Sag) |
| Thermistor / NTC Sensor | 10kΩ - 100kΩ @ 25°C | Smooth Thermal Curve | 0Ω (Short) or ∞ (Open) |
| Safety Ground / PE Continuity | < 0.5Ω Resistance | Solid Earth Bond | > 1.0Ω (Floating Chassis) |
Common Symptoms & Fault Manifestations
- Inverter disconnects from grid and stops AC generation
- Alarm LED illuminates red and LCD displays error F18
- Audible internal relay clicking as the unit attempts reconnect cycles
Root Causes & System Failure Modes
PV array insulation resistance degraded below 100kΩ due to damaged cable jackets or moisture ingress
Parasitic capacitive coupling to earth from damp PV modules in high-humidity morning conditions
Poor or severed AC ground/PE bonding causing ground-potential floating
Defective internal Hall-effect leakage current sensor or main control board failure
High-Voltage & Mechanical Safety Isolation
Prior to opening access panels, disconnecting terminals, or probing wiring, perform complete lock-out / tag-out (LOTO). Disconnect all AC mains, DC string isolators, and lithium battery banks. Allow internal smoothing capacitors at least 3 to 5 minutes to dissipate stored residual energy below safe threshold (<30VDC).
Step-by-Step Diagnostic & Resolution Procedure
Safe Isolation & Residual Energy Discharge
Shut off the AC grid breaker, battery DC isolator, and turn the integrated PV DC switch to OFF. Wait at least 10 minutes for internal DC-bus capacitors to drop below 36V before opening wiring compartments.
PV Array Insulation & Earth Resistance Test
Disconnect all PV strings from MPPT1 and MPPT2 inputs. Set the Megohmmeter to 1000V DC and test insulation resistance between PV+ to PE and PV- to PE on each string; ensure readings exceed 1MΩ. Repair any pinched wiring or moisture-compromised junction boxes if resistance is below 100kΩ.
AC Side Earth & Neutral Integrity Check
Verify continuity and low impedance (<1Ω) from the inverter PE terminal to the main distribution earth bar. Check that Neutral and PE are not bridged incorrectly downstream of the inverter output switchboard.
Individual String Reconnection & Operational Verification
Power on the inverter with AC and battery only. Reconnect PV strings one by one to isolate which array branch triggers the F18 trip. If the fault persists with no PV strings connected, the internal RCMU sensor is faulty and requires inverter replacement.
Hardware Reset & Fault Clear Sequence
Controller ProcedurePrevention & Routine Maintenance Guidelines
- Ensure all rooftop DC conduit fittings and MC4 connectors meet IP65/IP67 weatherproofing standards to prevent water ingress.
- Verify panel frames and mounting racking are bonded with dedicated copper earth conductors to stabilize capacitive leakage.
Frequently Asked Diagnostic Questions
What does error code F18 indicate on Deye SUN-12K-SG04LP3?
Error F18 indicates that the residual current monitoring unit (RCMU/GFCI) detected an AC or DC leakage current to ground exceeding the safety limit (typically >30mA continuous or >300mA instantaneous spike), triggering an emergency disconnect from the grid. In engineering telemetry, it indicates gfci leakage current trip requiring circuit verification.
What are the primary triggers causing error F18?
Diagnostic bench telemetry isolates the following common root causes: PV array insulation resistance degraded below 100kΩ due to damaged cable jackets or moisture ingress; Parasitic capacitive coupling to earth from damp PV modules in high-humidity morning conditions; Poor or severed AC ground/PE bonding causing ground-potential floating; Defective internal Hall-effect leakage current sensor or main control board failure.
How do I reset and clear Deye error F18?
Turn off PV switch, battery breaker, and AC isolator. Wait 5 minutes until screen completely powers down. Turn AC on, battery on, and finally PV switch on. Enter LCD Settings > Advanced > Clear Faults. If the error status repeats immediately after clearing, discontinue clearing and test circuit continuity.
Can I safely resolve error F18 without specialized shop tooling?
This fault is graded as Advanced difficulty with High severity. Standard diagnostics require an insulated digital multimeter and appropriate hand tools. Always observe high-voltage isolation procedures.