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AS/NZS 3000-2018
Earth Leakage in Solar Systems — Three Protection Approaches
Earth leakage protection in a solar installation must address both the AC side (post-inverter) and the DC side (array to inverter). These two circuits require different protection approaches because standard AC RCDs cannot detect DC leakage.
AC Side — RCD/RCBO (Type A minimum)
The AC circuit from inverter to switchboard is protected by a Type A RCD or RCBO rated at 30 mA. This protects against:
Insulation breakdown in the AC cable run
Touch current from exposed inverter terminals
Ground faults in the inverter's AC output circuit
DC Side — Ground Fault Detection (Inverter-Integrated)
Transformerless inverters have a built-in Ground Fault Detection (GFD) circuit that monitors leakage current between the floating DC circuit and the earthed inverter chassis. This provides equivalent protection to an RCD but works in the DC domain. The inverter will shut down and display a fault code if DC leakage exceeds approximately 300 mA.
Isolation Transformer Systems — IMDs
Where the installer specifies an isolation transformer between the solar array and inverter (rare in residential; more common in commercial systems with galvanic isolation requirements), the DC side of the transformer is unearthed. An Insulation Monitoring Device (IMD) must be installed on the DC side to detect the first earth fault before it becomes a double-fault hazard.
Protection Device | Circuit | Trip Threshold | Reset |
|---|---|---|---|
Type A RCD | AC solar circuit | 30 mA | Manual (trip button) |
Inverter GFD | DC array | ~300 mA | Manual reset on inverter after fault cleared |
IMD (isolated DC) | DC side of isolation transformer | Typically 1–10 kΩ to earth | Alarm — may be manual or automatic |
Engr. Jason Morales — Founder, SolarEnergyPH
