An example demonstrates the earthing problem. A 12 AWG wire
from wall receptacle maybe 50 feet back to mains box has less
than 0.2 ohms resistance. That same wire would have something
like 120 ohms impedance. Lets say a tiny 100 amp transient
seeks earth ground via that 50 foot wire. Therefore a wall
receptacle - and adjacent electronics - will be at something
less than 12,000 volts. Will that transient seek earth via
that safety ground wire? Of course not. It will also seek
other and destructive paths via adjacent electronics.
Wire length is but one reason why a wall receptacle safety
ground is not sufficient as earth ground. Also explains why
plug-in protectors are so ineffective.
Essential to minimizing wire impedance are wire length, no
sharp bends, and other characteristics cited previously. Also
important is a concept cited by Bud--
Clamping all incoming wires to the same the same ground
reference is the best way I know to protect electronics. ...
The quality of a service entrance protector is only as
effective as its earth ground which is why distance to that
earthing is so critical and why single point earthing is
essential. That means the 6 AWG wire does not go up over a
foundation and then down to an earth ground rod. That wire
goes through foundation somewhere just above the ground rod so
that wire distance is shorter with sharp bends eliminated.
Also important is that earthing wire remain separated from
other non-earthing wires to avoid induced transients.
Yes, lower resistance does help which is why high
reliability facilities such as electric substations expand
their earth ground to also lower resistance. It is also why
earthing should be planned when the footing are poured.
Equipotential being another aspect of superior earthing.
Unfortunately we still don't build as if the transistor
exists. We still do earthing as an afterthought. Effective
earthing addresses concepts in excess of that performed by
conventional household earthing. Equipotential being a
concept of transistor protection that is not as essential to
human protection. If we built buildings for effective
transistor protection, then Ufer grounds would be routine; and
not some afterthought to supplement water pipe ground such as
ground rods. Even water pipe would enter a building adjacent
to all other utilities to contribute to transistor safety.
Even NEC requires all incoming electrical utilities be
earthed to a common point for human safety - a problem still
found even in some new homes.
That 20 foot requirement from NEC is article 800.40(A)(4):
Length. The primary protector grounding conductor shall
be as short as practicable. In one- and two-family
dwellings, the primary protector grounding conducutor
shall be as short as practicable, not to exceed 6.0
meters (20 ft) in length.
Same paragraphs is also found in Article 820.
Cinergy demonstrates how to solve earthing problems created
when utilities arrive at wrong locations. A problem often
created by service installers or builders who still have not
learned about proper earthing:
http://www.cinergy.com/surge/ttip08.htm
Concrete encased grounding (Ufer grounds) were so well
proven even before WWII as to even protect munitions from
direct lightning strikes. If water pipe earthing was so
effective, then why do they implement Ufer grounding even in
buildings with water pipe grounds? Halo grounds are but
another way of improved earthing.
Again, to answer the original poster's question - water pipe
earthing alone is no longer sufficient to meet code. Upgrade
to accomplish more than just meet code. Transistor protection
is only as effective as a building's earth ground.
Bud-- wrote:
As I said protector blocks for cable and TV should be immediately
adjacent to the panel so all wiring is clamped to the same ground
reference. You don't explain how a ground rod would help in this
instance. Adding a ground rod near the FAX is not going to provide
a low impedance to keep the ground reference for the FAX the same
as the incoming neutral.
...
Incoming utilities listed have to have protector blocks near the power
panel to get a common grounding reference.
How does a 10 foot wire to a high resistance ground rod provide a lower
ground impedance than a grounding electrode conductor and water pipe?
This is cental to your arguments. Perhaps you could explain and also
provide some citations that support your view.
For a 500A service the conductor to a ground rod has to be #6. The
conductor to a water pipe has to be 2/0 - 3.5 x the area. How come?
Surges include high frequency components for which impedance is
important. Grounding electrode conductor and water pipe has one
function of limiting surges.
Another problem with using a cold water pipe as an earth
ground connection - code wants each utility to be earthed less
than 20 feet to the common point.
Cite the code.
...
Clamping all incoming wires to the same the same ground reference
is the best way I know to protect electronics. That requires the
protector blocks to be near the electrical panel. (More properly
thay have to be near each other.) That is likely a lot more
important than resistance or impedance to ground. If all wiring
was clamped to the same reference with no ground connection could
electronics see a difference.
Gfretwell has posted how homes are now being built so as to
provide superior transistor safety in pictures at:
http://members.aol.com/gfretwell/ufer.jpg
This is a concrete encased electrode which I said is probably the second
best electrode (after water pipes). It is one of 3 electrodes that must
be included in a ground system, if present. (The other 2 are water pipe
and building steel, which a home doesn't have.) Not included: ground rod.
Another also demonstrates better earthing. None of this
would be required if city water pipe was sufficient as earth
ground for transistor safety:
http://www.knology.net/~res0958z/
Most of us don't put 55 foot high lightning rods in our back yard. Not
particualrly relevant.
-------------
With regard to: Bud-- does not even quote code to justify his post. You
do not understand why water pipes are required to have a SUPPLEMENTAL
electrode and don't listen to people who do understand. Since arguing
the code is pointles, I tried Physics - ground resistance. That doesn't
seem to work either.
bud--