"Tom Horne, Electrician" wrote:
W Tom
You keep making that statement even though you've been corrected
several times. It is a disservice to the DIY community to
repeatedly say "Water pipe is no longer acceptable as an earth
ground." The US National Electric Code (NEC) requires that any
underground metal water pipe that is ten or more feet in length
shall be used as a grounding electrode. I know that you will now
try to muddy the water by bringing up the requirement for a
supplemental electrode but the fact is that regardless of how
many electrodes you have you must use the underground metal water
pipe as a grounding electrode if it is available on the premise.
You can argue all you want but until the Code Making Panel that
is responsible for chapter 250 of the US NEC changes the code
underground water piping must be used as a grounding electrode
in any locality that has adopted the NEC as that localities code.
w_tom wrote:
You have it backwards, Tom. Previously you made that
claim. Others then noted why you were wrong. Even if a home
is earthed by a water pipe, that water pipe is no longer
sufficient for earthing (exception is legacy conditions). The
code requires bonding to water pipe - grounding for human
safety. The code is quite specific as to what is required for
an earthing electrode.
I don't expect to change Tom Horne's opinion - having
previously quoted code. But for the benefit of others, the
code says in Article 250.53(D)(2):
Supplemntal Electrode Required. A metal underground water
pipe shall be supplemented by an additional electrode of a
type specified in 250.52(A)(2) through (A)(7).
Those six electrodes are 2) Metal Frame of the Building or
Structure, 3) Concrete Encased Electrode (also called Ufer
grounds), 4) Ground Ring (also called Halo ground), 5) Rod and
pipe Electrodes (also called a copper clad ground rod), 6)
Plate Electrodes, or 7) Other Local Metal Underground Systems
or Structures.
If earthed only to a water pipe, then a building does not
have sufficient earthing. If no water pipe exists, any of the
above ground electrodes 2 through 7 are sufficient - need not
be supplemented. The water pipe is no longer sufficient for
earth ground which is why it must be "supplemented". The
Original Poster is advised to install earthing as required by
post 1990 code. This for two reasons - human safety (per
code) and transistor safety (which code does not address).
Building's occupants also want transistor safety.
Therefore a second reason why water pipe earthing is often
insufficient as an earth ground.
The code says water pipe earthing (which was standard before
19909) is insufficient. Appliance protection also demands an
adjacent earthing electrode for other reasons electrical. Two
reasons why water pipe earthing is no longer sufficient. NEC
requires water pipe be bonded to AC electric safety ground -
for human safety reasons. NEC requires other electrodes (2
through 7) for earthing.
Robert11: volts500 also posted a description of other
safety grounds in a post entitled "Grounding Rod Info" in the
newsgroup alt.home.repair on 12 July 2003 at
http://tinyurl.com/hkjq
Quoting only part of the applicable section of the code does you no
credit. I know what your opinion is as do most of the long time
contributers here. What I'm talking about is what the US National
Electric Code requires. While it is true that the code requires interior
metal water piping to be bonded to the neutral of the service it also
requires that any underground metal water piping that is ten or more
feet in length be used as a grounding electrode. The reason that the NEC
requires a supplemental grounding electrode is stated in the handbook
thusly. The portion in brackets & italics is the handbook commentary.
[The requirement to supplement the metal water pipe is based on the
practice of using a plastic pipe for replacement when the original metal
water pipe fails. This type of replacement leaves the system without a
grounding electrode unless a supplementary electrode is provided.] In
other words a driven rod electrode is better than nothing.
Thus it is the risk of later replacement with plastic piping that is the
reason for requiring that the underground metal water piping be
supplemented with another type of grounding electrode. By actual
measurement the underground metal water piping system provides a far
lower resistance to earth than eight or ten foot driven rods.
[Section 250.50 introduces the important concept of a “grounding
electrode system,” in which all electrodes are bonded together, as
illustrated in Exhibit 250.21. Rather than relying totally on a single
electrode to perform its function over the life of the electrical
installation, the NEC encourages the formation of a system of electrodes
“if available on the premises.” There is no doubt that building a system
of electrodes adds a level of reliability and helps ensure system
performance over a long period of time.]
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.
Exception: In industrial and commercial buildings or structures where
conditions of maintenance and supervision ensure that only qualified
persons service the installation, interior metal water piping located
more than 1.52 m (5 ft) from the point of entrance to the building shall
be permitted as a part of the grounding electrode system or as a
conductor to interconnect electrodes that are part of the grounding
electrode system, provided that the entire length, other than short
sections passing perpendicular through walls, floors, or ceilings, of
the interior metal water pipe that is being used for the conductor is
exposed.
(2) Metal Frame of the Building or Structure. The metal frame of the
building or structure, where effectively grounded.
(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm
(2 in.) of concrete, located within and near the bottom of a concrete
foundation or footing that is in direct contact with the earth,
consisting of at least 6.0 m (20 ft) of one or more bare or zinc
galvanized or other electrically conductive coated steel reinforcing
bars or rods of not less than 13 mm (˝ in.) in diameter, or consisting
of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4
AWG. Reinforcing bars shall be permitted to be bonded together by the
usual steel tie wires or other effective means.
(4) Ground Ring. A ground ring encircling the building or structure, in
direct contact with the earth, consisting of at least 6.0 m (20 ft) of
bare copper conductor not smaller than 2 AWG.
(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less
than 2.5 m (8 ft) in length and shall consist of the following materials.
(a) Electrodes of pipe or conduit shall not be smaller than metric
designator 21 (trade size 3/4) and, where of iron or steel, shall have
the outer surface galvanized or otherwise metal-coated for corrosion
protection.
(b) Electrodes of rods of iron or steel shall be at least 15.87 mm (5/8
in.) in diameter. Stainless steel rods less than 16 mm (5/8 in.) in
diameter, nonferrous rods, or their equivalent shall be listed and shall
not be less than 13 mm (1/2 in.) in diameter.
(6) Plate Electrodes. Each plate electrode shall expose not less than
0.186 m2 (2 ft2) of surface to exterior soil. Electrodes of iron or
steel plates shall be at least 6.4 mm (1/4 in.) in thickness. Electrodes
of nonferrous metal shall be at least 1.5 mm (0.06 in.) in thickness.
(7) Other Local Metal Underground Systems or Structures. Other local
metal underground systems or structures such as piping systems and
underground tanks.
(B) Electrodes Not Permitted for Grounding. The following shall not be
used as grounding electrodes:
(1) Metal underground gas piping system
(2) Aluminum electrodes
--
Tom Horne
Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.