w_tom wrote:
One plumber need only replace copper pipe in plastic. The
human taking a shower or bath is then at extreme risk if the
wall receptacle safety ground has been connected to those
pipes.

The connection from breaker box to cold water pipe is
required by code to remove electricity from that pipe. There
is no way that connection can be reliable to a wall receptacle
because copper pipe is often replace with plastic. The only
way a wall receptacle can make a safe connection to the water
pipe is to make the connection adjacent to where that water
pipe also connects to breaker box. The connection authorized
by NEC article 250.

All of this being completely irrelevant to the earth ground
electrode system. Wall receptacles are safety grounded. That
means they must connect to breaker box bus bar. Earthing
electrode or a water pipe in contact with earth does nothing
to provide a safety ground to that wall receptacle.

In places such as Canada, grounding to water pipes is still
permitted by code. But the point is (and I believe HorneTD is
making the same point), that wall receptacle must be grounded
by a method that cannot be 'accidentally' compromised.
Leaving the wall receptacle ungrounded is safer than putting a
human in bathtub at risk.

Again a safer solution is to GFCI the circuit even if or if
not connecting wall receptacle to cold water pipes. The wet
human is the human at greatest risk. So we connect a
potential electric circuit to bathtub pipes? Not smart at
all.

It does not have to be what either of us believe is smart to be what is
required by law. If the US National Electric Code (NEC) is adopted by
reference as law in your location then you have to use any underground
metal water pipe that is three or more meters in length as part of the
grounding electrode system. It does not matter if in your or my opinion
that imperils someone in the shower or bath. You have never to my
knowledge accepted the point that whether the water piping in the
building is metallic does not effect the requirement to use that
underground metal water piping as a grounding electrode. That
underground metal water piping is for many homes the only effective
earth grounding electrode. I have been doing electrical work for nearly
forty years and I have never encountered a municipal water system with a
resistance to ground of more than twenty ohms. During that same time I
have never had a single or double driven rod electrode of ten feet per
rod or less measure less than fifty ohms. The best grounding electrode
is going to be the one that puts the most conductive surface in contact
with the earth at the deepest level. For many buildings that is the
metal service lateral of the water supply.
--
Tom H