Cruciform and star shaped sections are also available and are more rigid while being driven, but the apparent additional surface does not confer a noticeable advantage in current-carrying capacity or reduction of resistance. In circumstances where it is convenient to do so, the addition of radial strips will be advantageous. Such rods may be coupled together to give longer lengths. Except in special conditions, a number of rods in parallel are to be preferred to a single long rod. Deeply riven rods are, howver, effective where the soil resistivity decreases with depth or where substrata of low resistivity occur at depths greater than those with rods, for economic reasons, are normally driven. In such cases the decrease of resistance with depth of driving may be very considerable as is shown by the measurements plotted in Fig. 12 for a number of sites; for curves A1 and A2, it was known from previously sunk boreholes that the soil down to a depth between 6 and 9 m consisted of ballast, sand and gravel below which occurred London clay. The rapid reduction in resistance, when the electrodes penetrated the latter, was very marked. The mean resistivity up to a depth of 8 m in one case was 150Ωm; at 11 m the mean value for the whole depth was 20 Ω m moving to the low resistivity of the clay stratum. Similarly for curve C, the transition from gravely soil to clayey at a depth of about 1·5 m was very effective. We, at Atul Casting and Metal Works manufactures all earthing related products such as G.I Strips, G.I plates, G.I Rods, G.I Pipes, C.I covers, Cable Trays, G.I Wire, Manhole Covers and Route Markers for past 50 + Years in heart of New Delhi. Call us at +91 9873361672 for best deals