Handbook of Electrical Engineering

EARTHING CURRENT AND ELECTRIC SHOCK HAZARD POTENTIAL DIFFERENCE 591

Figure H.1b Corner mesh potential versus the number of meshes.

Ifρais calculated to be close toρthen takeρato equalρas a conservative estimate, therefore
ρa=1000 for this example.

Now find the total amount of material to be used in the grid and rods.

The total lengthLrof the ground rods is:-

Lr=(Nrod1+Nrod2)lr=200 m

Note, let the total number of rods beNrodwhich equalsNrod1+Nrod2.

The total lengthLgof the grid conductors is:-

Lg= 2 nlgrid=120 m

Wherelgrid=(n− 1 )dspis the buried length of one side of the grid, which is 10 m. The
integer ‘n’ is the number of nodes on one side of the grid, or the number of meshes in one side
plus 1.

The total length of buried rods and grid conductors including bonding connections is the
weighted totalLc:-
Lc=Lg+ 1. 15 Lr=350 m

Having now obtained the lengths of rods and grid conductors it is now possible to calculate
the ground resistanceRepusing equations 41, 42, 43, 44 and 46 from sub-section 12.3 of IEEE80.