Hi All,

Apologies if this has been answered previously & forgive me for my lack of knowledge on generators.. However we are currently involved in a project on a new school building that has a 275Kva backup generator. Due to delays with the DNO, The generator is likely to supply the building on a permanent basis until at least the end of the year. 

It's currently situated around 20 m from the building and we have parallel 95 m4 core SWAs from the generator to the ATS switch. 

We have a specialist earthing company coming in to give us an earth array for the generator & They seem to think they can give us around 1 ohm resistance. 

What i can't quite grasp, Is whether I'm right thinking that that one ohm value on the earth array has nothing to do with the loop Impedance we will be getting to the building as this Should solely be based on our L-E resistance back to the star point of the generator? 

If I am completely missing something & our Ze value at the building when fed via the generator will be 1ohm minimum, then we need to ensure correct final circuit protection (IE 30mA RCBOs) on the majority of final circuits that will exceed the maximum ZS values to meet disconnection times.

Any advice would be greatly appreciated.

Thanks,

Tim