RBE
I would check the incoming earthing first, just to see how good or poor the earth is. If the origional installation is conventional and you can take an earth loop reading, you really will have to stick to the Less than 0.8 ohm rule.
However having experience with a conventional setup in...
Working for a local REC I would suggest the TT system ,and earth spike each and every shed . This will prevent as mentioned tranfering earth fault currents and will prevent reverse polarity problems occuring with the pme system. Most overhead installations have been found to have poor or non...