w_tom wrote:
Water pipe makes a good low resistance ground. Human safety
demands a low resistance ground for reasons that include, for
example, neutral wire failure.
Transistor safety uses grounding components for a different
purpose. Transistor safety requires a low impedance ground.
If connecting a bonding wire to a water pipe 50 feet away, the
house has a low resistance ground and a high impedance
ground. High impedance means ineffective transistor
protection. Take this fax machine protection as an example:
http://www.epri-peac.com/tutorials/sol01tut.html
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.
For
transistor safety, all incoming utilities (telephone, cable
TV, satellite disk) must make a less than 10 foot connection
to this common earthing point.
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.
A most common source of transistor destructive transients to
things such as computer modems is incoming on AC electric.
Wires highest on poles - AC electric - are more often struck;
not lower cable and phone line. If that 'arrestor' does not
connect AC electric wire to earth ground, then a transient
(again in that picture) goes into fax machine (modem) on L
connection, then destructively out on phone wires to NID and
to earth ground. Above demonstrates why fax machines, modems,
and portable phone bases stations are so often damaged by AC
electric wire transients.
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.
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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--