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I have discussed this with a colleague much better versed in earthing matters. He suggests that you:

a) connect neutral and earth at the generator only

b) use an RCD (say 100mA) for the main isolator

c) use further RCD protection (30mA) on socket circuits

d) bond pipes to earth where they enter the building; supplementary bonding (metal sinks, etc) is not required

Images and details can be found in https://www.pat-services.co.uk/iee-guidance-note-7-bs7671-1697.htm

Earth loop impedance (Ze) at the load should be less than 0.35 ohms (this will be via the generator) Test the resistance of the earth electrode separately. With damp soil a 4 foot electrode should give less than 20 ohms. If not, bond it to a second one about a foot away.

Lightning earth system should be kept separate from distribution earth and resistance as low as possible, certainly no higher than distribution earth resistance.

Duncan Kerridge