Q & A of the Day - Will this solar array need an extra earth?

Question: I'm quoting for a ground-mounted photo-voltaic (PV) array, which is some distance from the house. As the system is basically a generator in its own right (albeit one that will only produce electricity in tandem with the mains supply), will it need an additional earth, spiked into the ground?

The house has a TT earthing arrangement, and the array will be closer to the sub-station than the house. Surely, there must be a possibility (should an earth fault occur), that the shortest path will be through to the array framework?

Answer: The PV array would not normally be earthed as the protective measure in Section 712 of BS 7671: 2008 Regulation 712.requires that protection by the use of class II or equivelant insulation shall preferably be adopted on the DC side as the protective measure - the AC side of the installation will be earthed at the connection to equipment on the load side of the installation, and may also require RCD protection.

Regulation 712.312.2 does, however, allow earthing of one side of the live conductors of the DC side if at least simple separation of the DC and AC sides is achieved. However, the regulation notes that where such connections are made, these should be such that corrosion is avoided and refers to BS 7361-1:1991 Code of Practice for cathodic protection.

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