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Table 1: Testing - soil conditions, TT Systems and Uo of 230 V only
Max value rod
protection in installation 		Max electrode
value in BS 7671		 2 m rod Max value
in dry period		 3 m rod Max value
in dry period		 2 m rod Max value
in normal rainfall		 3 m rod Max value
in normal rainfall
mA          
30 1666 1110 1666 410 1100
100 500 333 500 125 333
300 166 110 166 42 110
500 100 66 100 25 66
It is suggested that 3 m electrodes at 2 m depth during installation to establish a reasonably linear soil resistivity profile