I noticed that a light switch back box measured around 100V ac w.r.t. the cold water tap in our recently-purchased house. I checked the earth bonding on the metal pipework for the hot and the cold tap and the radiator; all are at the same zero volt potential. I checked the earth of a nearby mains socket and saw no p.d. between it and the pipework mentioned. I looked around the house and I see lots of earth bonding that has been carried out within the last 3-4 years.
Measuring a current flow to ground from this "dodgy" earth, I see a couple of hundred microamps flowing (actually about 275uA). Not enough to hurt but you can just about feel a "buzz" on your finger tip.
I shall start trying to trace the lighting ring main back, but I am puzzled as to why this lighting ring earth should float when a nearby socket ring main earth doesn't. I am yet to carry out furthr investigations i.e. other looking at other ring circuits.
Maybe this is a simple fix but I'd appreciate some guidance before I get up loads of floorboards etc.
thanks in advance