It is a common trend to earth the shield of transformer at one point, to eliminate the circulating 3rd harmonics within the shield itself.
But, if it is shielded cable, many belieive to be earthed on one point only, but, I believe that earthing at 2 ends of shield in Shielded cable shall reduce the noise more effective way as compared to that of earthing at one point of shield.
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Exploring the Science of Electricity