Sofar Grid Disconnection Fault — G98/G99 Voltage & Frequency Trip Diagnosis
Your Sofar inverter keeps dropping off the grid with a fault alarm. It's not failing — it's protecting the network. Grid overvoltage, frequency excursion, or isolation fault — each has a different cause and fix. This guide walks through how to read the fault codes and determine what's happening.
We review your SolarMan event log, check grid code configuration, and determine whether the trips are caused by grid voltage, system settings, or an isolation fault.
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Important: A grid disconnection is a safety function, not a system failure. Your Sofar inverter is doing exactly what the UK grid code requires — disconnecting when voltage or frequency exceeds safe limits. The system reconnects automatically when conditions normalise.
5-step grid disconnection diagnosis
Sofar inverters report grid faults with specific codes: G-OV (overvoltage), G-UV (undervoltage), G-OF (overfrequency), G-UF (underfrequency), and G-ISO (isolation fault). The code tells you exactly which diagnostic path to follow.
Check SolarMan for the grid fault code
Log into SolarMan and navigate to the alarm or event history. Find the grid disconnection event and note:
For ME3000SP units, check the LCD display for the most recent fault code. The ME3000SP logs faults locally as well as in SolarMan (if the datalogger is connected).
Determine if the fault is grid quality or isolation
Grid disconnection faults split into two distinct categories:
The AC grid voltage or frequency has exceeded statutory limits. This is an external issue — the local electricity network is out of specification. The inverter disconnects as required by G98/G99 and reconnects when conditions normalise.
The insulation between DC circuits and earth has degraded. This is an internal system issue — water ingress into connectors, damaged cable insulation, or a battery module fault. Requires on-site testing with an insulation resistance meter.
The diagnostic path is completely different for each category. Grid quality faults require monitoring and possibly DNO engagement. Isolation faults require on-site DC testing.
Check the grid code configuration
In SolarMan, check the grid code setting under device configuration:
If the inverter still has a factory default grid code from another country, the voltage and frequency thresholds will be wrong — causing disconnections at voltages that are normal for the UK grid. This is particularly common on recently installed or replaced Sofar inverters where the commissioning was incomplete.
Grid code settings require installer-level access in SolarMan. If you need to change it, contact STS or a qualified installer.
Monitor voltage patterns over 3–5 sunny days
If the fault code is G-OV, track the AC voltage in SolarMan across several sunny days to establish a pattern:
For HYD hybrid systems with battery storage, switching to self-consumption mode during peak solar hours can reduce export and lower your contribution to local voltage rise.
Contact your DNO or configure export limiting
If grid overvoltage is persistent, you have two parallel options:
Export limiting reduces your Smart Export Guarantee income but keeps the system connected during periods when it would otherwise trip. For HYD systems with battery, self-consumption priority achieves a similar effect by charging the battery instead of exporting.
Sofar grid faults — HYD hybrid vs ME3000SP
Sofar has two distinct product families in the UK, and grid disconnection faults manifest differently on each. The HYD hybrid series (HYD 3600–6000 EP) are all-in-one inverters that handle solar MPPT, battery management, and grid connection. They report grid faults through SolarMan with detailed voltage and frequency data. Because HYD systems have battery storage, they have a built-in advantage — excess solar can charge the battery instead of exporting, reducing contribution to local voltage rise.
The ME3000SP is an AC-coupled system that sits alongside a separate solar inverter. It manages battery charge and discharge but does not control the solar inverter's grid connection. If the solar inverter trips on grid overvoltage, the ME3000SP continues operating normally — it only trips if the voltage exceeds its own AC coupling point limits. This means you may see the solar inverter disconnecting while the ME3000SP stays online, or vice versa, depending on where the voltage threshold is breached first.
For both product families, the underlying cause of grid overvoltage trips in the UK is the same: grid infrastructure that was not designed for the level of distributed solar now connected to it. As solar installations increase in suburban areas, the cumulative export during peak hours pushes local voltage above G98 limits. This is a network-level problem, not a Sofar fault.
Grid disconnection fault — common questions
Sofar inverters disconnect when grid voltage or frequency exceeds G98/G99 limits. The most common UK cause is grid overvoltage at midday — local voltage rises above 253V when multiple solar systems export simultaneously. This is a grid infrastructure issue, not an inverter fault. The system reconnects automatically when conditions normalise.
G-OV is grid overvoltage (above 253V). G-UV is undervoltage (below 207V). G-OF is overfrequency (above 52Hz). G-UF is underfrequency (below 47.5Hz). These are G98 protection thresholds — the inverter disconnects automatically when any is exceeded for more than 200 milliseconds and reconnects when conditions return to normal.
For HYD hybrids, log into SolarMan and check the alarm or event history — each disconnect is logged with the fault code, timestamp, voltage, and frequency. For ME3000SP units, check the LCD display or SolarMan if the datalogger is connected. The code tells you whether the trip was grid quality (G-OV/UV/OF/UF) or isolation (G-ISO).
No. Grid disconnection is a designed safety function. The inverter disconnects to protect both the system and the grid — no damage occurs. Frequent trips reduce generation during disconnect periods but do not cause wear or degradation. The system reconnects and resumes normal operation automatically.
G-ISO means the insulation resistance between DC circuits and earth has fallen below the safety threshold. Unlike grid voltage faults, this is internal to your system. Common causes include water ingress into MC4 connectors, UV-damaged cable insulation, or a battery module fault. A G-ISO fault requires on-site testing with an insulation resistance meter. Book a diagnostic and we'll confirm the cause.
Sofar inverter keeps tripping off the grid?
We review your SolarMan event log, check grid code configuration, and determine whether the trips are caused by grid voltage, frequency, or an isolation fault. Clear diagnosis, clear next steps.
Return to the Sofar brand hub to explore other common faults and services.
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