The bit that says "Ufer earthing equipotentially bonds a house's concrete slab floor to the electrical earthing system, eliminating the risk of shock from the CPC or equipotential bonding to floor. This risk exists with TT systems where a floor slab is damp, and to a lesser extent with PME supplies."
could do with a bit of refinement I think. "Risk of shock from the CPC" I suspect you are referring to reducing shock risks from "indirect contact" caused by high touch voltages present on earthed metalwork in the property, when a phase to earth fault exists.
This risk is *lowest* with TT systems due to the level of RCD protection.
The need for EQ bonding on PME supplies is the greatest, and having multiple redundant earth connections is a "good thing" since it reduces touch voltage should the suppliers neutral connection be disconnected.
--John Rumm 03:03, 16 June 2007 (BST)
I'd think risk is highest with TT systems as there are many around with no RCD or even ELCB. And those that have them are not perfectly protected, as there are various failure-to-act modes for ELCBs & RCDs.
In new builds the picture is quite different, as you say. But given so few DIYers ever install Ufer earthing I guess its mostly academic. I think Ufers are primarily retrofitted by DIYing radio hams, who will generally be using existing wiring installations rather than new, so I suspect in practice TT systems are the biggest risk. NT 09:44, 16 June 2007 (BST)