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Originally Posted by Retlaw

The water in the pipes comes from the ground, so any copper pipe carrying water, must eventully be grounded, back through the system whether its a central heating pipe or what. Gas pipes from the mains supply were made of steel and when that was laid it was lagged to prevent corrosion, now gas pipes laid in streets are plastic, so wheres the earth on a new gas pipe.
Retlaw

Retlaw

http://www.plasticpipesgroup.com/pdfs/earthbonding.pdf