A rooftop on-grid solar system needs a DC earth, an AC earth and a lightning earth, run from the roof down to earth pits at ground level and bonded to the building earth. Keeping the solar earths tied to the existing building earth prevents a potential difference between the array and the rest of the installation.
The earths you need
- DC earth for module frames, structures and inverter DC side.
- AC earth for the inverter output and the on-grid meter and board.
- Lightning earth for the air terminal protecting the array.
- All bonded to the building main earth terminal.
Running the conductors
Bring earth conductors from the roof down an external route to dedicated earth pits, keeping lightning down-conductors straight. Use copper for the lightning path and sized GI or copper for the system earths. Aim for an overall earth resistance of a few ohms or less.
