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.

HorneTD wrote:
w-tom
I realize that we may disagree on this but since the US NEC specifically
requires the use of underground metal water piping as part of a
building's grounding electrode system don't you think it would be
clearer to say "interior metal water piping" when saying metal water
piping should not be used as a ground for an electrical system. The
code specifically permits the equipment grounding conductor that is
installed as a retrofit ground to run to any electrode of the grounding
electrode system vis..

[VII. Methods of Equipment Grounding
250.130 Equipment Grounding Conductor Connections.
Equipment grounding conductor connections at the source of separately
derived systems shall be made in accordance with 250.30(A)(1). Equipment
grounding conductor connections at service equipment shall be made as
indicated in 250.130(A) or (B). For replacement of non–grounding-type
receptacles with grounding-type receptacles and for branch-circuit
extensions only in existing installations that do not have an equipment
grounding conductor in the branch circuit, connections shall be
permitted as indicated in 250.130(C).
(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions.
The equipment grounding conductor of a grounding-type receptacle or a
branch-circuit extension shall be permitted to be connected to any of
the following:
(1) Any accessible point on the grounding electrode system as described
in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the
branch circuit for the receptacle or branch circuit originates
(4) For grounded systems, the grounded service conductor within the
service equipment enclosure
(5) For ungrounded systems, the grounding terminal bar within the
service equipment enclosure(copyright 2002 National Fire Protection
Association)]

The point you are making is quite valid. The interior metallic piping
system must not be used as an equipment grounding or bonding conductor.
Having said that I have to take issue with the statement that "any
recommendation to connect safety ground to cold water pipes only creates
a potentially greater hazard." I realize that this is a fine point but
I believe it is important enough to be clear. The US NEC does not offer
any option. When an underground metal water pipe that is twenty or more
feet in length is available on the premise then it must be used as a
grounding electrode vis..

[250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used.
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in
direct contact with the earth for 3.0 m (10 ft) or more (including any
metal well casing effectively bonded to the pipe) and electrically
continuous (or made electrically continuous by bonding around insulating
joints or insulating pipe) to the points of connection of the grounding
electrode conductor and the bonding conductors. Interior metal water
piping located more than 1.52 m (5 ft) from the point of entrance to the
building shall not be used as a part of the grounding electrode system
or as a conductor to interconnect electrodes that are part of the
grounding electrode system. (copyright 2002 National Fire Protection
Association)]

Please note how carefully the Code Making Panel differentiated between
interior and underground water piping.
--
Tom H