question on earthing

[soulman]

Can you guy's explain to me if you isolate the supply at the c.u can there ever be a voltage sitting on the met. also if a gas or water pipe were to introduced a voltage to the building how is this voltage detected. i am just a little confused, and want to know how to recognize a dangerous situation. i have spoken to qualified sparks and one contradicts the other,

 

[ezzzekiel]

yes but only if something is very wrong (cross polarity on a pme for example)

if a voltage was introduced via a pipe then all pipework should rise to the same potential