help on Earthing groundmount PV array with rammed metal posts

[Morgan keith]

I'm installing an aluminium framed groundmount PV system with an SMA 17000TL inverter and wondering about the array frame earthing. The posts are rammed about 1m into the ground. Do I need to install an earth spike for each array. The Array is around 120m from the main dist panel and incomer point so have a 50mm 4 core SWA cable for the AC side. Do I need to install a seperate Earth spike for external DB installed at array or is SWA earthing sufficient?

Many thanks

 

[johnboy6083]

Can you not use the array itself as an electrode? try testing it, and see what resistance you get?

 

[Morgan keith]

Thanks, I was wondering if there'd be much benefit to installing an earth spike when there's already numerous big metal posts rammed much the same depth into the ground. You think I should just do an earth loop impedance test between the array frame and the new external DB supply?

 

[VMan]

Thanks, I was wondering if there'd be much benefit to installing an earth spike when there's already numerous big metal posts rammed much the same depth into the ground. You think I should just do an earth loop impedance test between the array frame and the new external DB supply?

My thoughts are the idea of bonding the array was to bring the array to same potential where it can be touched, not for so much fault protection, so i think if you have continuity throughout onto metal posts in the ground and the array, then the array will be at same potential where you are standing to touching the array, therefore no shock.

A earth fault loop impedance test will give you the fault loop impedance of the AC circuit, should a fault to the DC array frame occur from a nearby AC circuit. If no AC circuits are in the equipotential zone of the array ( which if the inverter is in different location to the array) then I cannot see the benefit of putting in an earth spike. Other may disagree.

But then again if you are banging supports into the ground for the array, is it much more effort to put a couple of spikes to cover your rear end?