Service Pipes showing 21volts AC to earth.

[Cnobby]

Hi,
At my mums house, she has been getting a slight shock from the metal shower valve. After she told me, i measured the shower valve to earth and had 5volts AC. I then went and measured the service pipes at the combi boiler to earth and there was 21volts AC present. There is no x bonds on these pipes. The earthing system is a TT. Could anyone give me some advice on what could be the likely cause here please? Many thanks chris

 

[The Truth]

those old ELCB's work on fault voltage rather than current..they are virtually useless...in fact if you test them with a normal RCD tester..you wont get them to trip thats how sensitive they are! so dont assume it works at all. and any way have to tested your earth rod? its impedance is prbly so massive that the fault current has no where to go except your pipework!

lighting circuit see?? what did i say? outside light full of water and shorting to earth?? globe lights melted cables? bad ceiling rose connections above light? damaged cable in a switch backbox? melted downlighter cable not easilly spotted?

just mega through it section by section and power up the good part of the circuit as you go