"Wes Stewart" wrote in message
...
On Wed, 8 Sep 2004 12:26:35 -0500, (Richard
Harrison) wrote:

|Jimmy wrote:
|"Using a cold water pipe is a bad idea and is not allowed by some local
|codes even though it may be allowed by the national code."
|
|You don`t want to be electrocuted when holding an electric appliance and
|a cold water valve simultaneously.

No kidding. I added a laundry room and attached garage to my house.
The former owner/builder had intentions to do something similar but
had not for whatever reason. He had stubbed out hot water from the
house (concrete slab on grade, pipes under slab) but not cold water.

I ran an exterior cold supply from the service entrance using PVC
underground and copper inside. I added another ground rod and 100' of
4 AWG buried at the base of the new footing and grounded the new cold
supply with it.

IMHO you can't have too many ground connections.
|
|My electric company, the former Houston Lighting and Power Company,
|writes:
|"All services shall be properly grounded. Note - NEC requires grounding
|to a "metallic underground water piping system" if available. Acceptable
|alternatives include a driven ground rod which is preferred by HL&P Co.
|regardless of the type grounding electrode used. NEC requires that the
|"interior cold water pipimg system" be bonded to it."
|
|Best regards, Richard Harrison, KB5WZI

Should re read what I write sometimes. I was refering to using the water
pipe as the sole ground for your electrical system. This used to be a common
thing and pemissable by the NEC, not sure if it still is.

Jimmie wrote:

Should re read what I write sometimes. I was refering to using the water
pipe as the sole ground for your electrical system. This used to be a common
thing and pemissable by the NEC, not sure if it still is.


When I replaced my service in 1975, a water pipe ground (which is all my
1952 house had) wasn't sufficient to satisfy the NEC, so I had to add a
ground rod. So the NEC hasn't permitted a water pipe ground as the sole
ground for at least 29 years. It apparently was permissible in 1952.

Roy Lewallen, W7EL

So the NEC hasn't permitted a water pipe ground as the sole
ground for at least 29 years.
Roy Lewallen, W7EL
=====================================

A good thing too. At any time a fully qualified plumber can come along and
replace a section of metal water pipe with polyethelene, one of the best
insulating materials known to science.

I am not very familiar with USA power-grounding regulations and they
probably vary from state to state. But I am under the impression that in
some simple circumstances, perhaps domestic, a single ground rod is
considered adequate for safety purposes.

Under similar circumstances a maximum ground electrode resistance ( whatever
its construction ) of 50 ohms is specified.

A 'standard' ground rod is 8 feet long and 1 inch in diameter.

An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec?

The calculated resistance of a single standard rod in average soil is 194
ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE
shelves. There ought to be greater use made of it. )

Now I don't expect the alarm bells to be rung from Washington to LA. But
isn't there a serious inconsistency somewhere?

As a matter of interest, the resistances to ground of 2, 3 and 4 rods in
parallel, spaced 6 feet apart in average soil, are as follows -

2 Rods = 113 ohms
3 Rods = 86 ohms
4 Rods = 70 ohms

all of which exceed the specified maximum of 50 ohms.

Quite a low average soil resistivity of about 130 ohms is needed to bring 50
percent of installations within specification.

If my starting data is wildly adrift then disregard my waffle.
----
Reg, G4FGQ

yeah, and its worse than that. most times they only use 1/2" or 5/8"
diameter rods, and the 6' spacing becomes 3' 'or so' when they do more than
one, which seems to be getting more common. the last electrician i hired
actually put 2 rods at a separate garage service entrance without being
prompted.... but maybe it was all the towers and other rods around that
convinced him he should do it right before i said anything.

"Reg Edwards" wrote in message
...
I am not very familiar with USA power-grounding regulations and they
probably vary from state to state. But I am under the impression that in
some simple circumstances, perhaps domestic, a single ground rod is
considered adequate for safety purposes.

Under similar circumstances a maximum ground electrode resistance (
whatever
its construction ) of 50 ohms is specified.

A 'standard' ground rod is 8 feet long and 1 inch in diameter.

An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec?

The calculated resistance of a single standard rod in average soil is 194
ohms. ( I'm sure the calculating formula can be found somewhere on the
IEEE
shelves. There ought to be greater use made of it. )

Now I don't expect the alarm bells to be rung from Washington to LA. But
isn't there a serious inconsistency somewhere?

As a matter of interest, the resistances to ground of 2, 3 and 4 rods in
parallel, spaced 6 feet apart in average soil, are as follows -

2 Rods = 113 ohms
3 Rods = 86 ohms
4 Rods = 70 ohms

all of which exceed the specified maximum of 50 ohms.

Quite a low average soil resistivity of about 130 ohms is needed to bring
50
percent of installations within specification.

If my starting data is wildly adrift then disregard my waffle.
----
Reg, G4FGQ

"Reg Edwards" wrote

I am not very familiar with USA power-grounding regulations and they
probably vary from state to state. But I am under the impression that in
some simple circumstances, perhaps domestic, a single ground rod is
considered adequate for safety purposes.

Under similar circumstances a maximum ground electrode resistance (
whatever
its construction ) of 50 ohms is specified.

A 'standard' ground rod is 8 feet long and 1 inch in diameter.

An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec?

The calculated resistance of a single standard rod in average soil is 194
ohms. ( I'm sure the calculating formula can be found somewhere on the
IEEE
shelves. There ought to be greater use made of it. )

Now I don't expect the alarm bells to be rung from Washington to LA. But
isn't there a serious inconsistency somewhere?

As a matter of interest, the resistances to ground of 2, 3 and 4 rods in
parallel, spaced 6 feet apart in average soil, are as follows -

2 Rods = 113 ohms
3 Rods = 86 ohms
4 Rods = 70 ohms

all of which exceed the specified maximum of 50 ohms.

Quite a low average soil resistivity of about 130 ohms is needed to bring
50
percent of installations within specification.

If my starting data is wildly adrift then disregard my waffle.
----
Reg, G4FGQ


Yes Reg, sorry the figures are (thankfully) in error. Especially since 25ohm
is required by our U.S. NEC, and that's easily attained in some soils, not
so easy in others. This is being changed in the 2004 code changes, but it
was paraphrased below:

The NEC does not specify a maximum earth resistance for the grounding
electrode system required under Article 250-81. The only place that does
specify earth resistance is under Article 250-84, for "made" (rod, pipe, and
plate) electrodes. Here the NEC specifies a resistance to ground of 25 Ohms
or less for a single electrode. If the electrode does not meet 25 Ohms, it
must be supplemented by one additional electrode. However the combination of
the two electrodes does not have to meet the 25 ohm requirement!

http://www.cpccorp.com/deep.htm

Neither should anyone be overly concerned with acheiving low DC-resistivity
of a grounded electrode. In spite of some interesting comments about their
perceived successes in the white paper I cited above, the grounding issue is
usually overstated - the ground for lightning is the real issue, as any 10'
5/8" copper rod earth ground works for 60hz electrical safety. For safe
termination of lightning downconductors and mast grounds etc, the best
ground you can reasonably achieve is going to be enough - as long as the
principles of bonding are adhered to religiously. That means as close to
equipotential as possible, and it does not assume a good ground, or even any
ground at all in certain cases. We surely want the best ground reasonably
attainable, and if you can sink 30' of connected rods, great. If you sink a
few 8-foot 5/8" or a couple of 1"x10', even better. See the data in that
paper above for some sample resistance measurements which they consider
"average" (ha - Richard Clark's laughing ;-), rightfully so.

Best regards,

Jack

On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter"
wrote:

http://www.cpccorp.com/deep.htm

See the data in that
paper above for some sample resistance measurements which they consider
"average"

Hi Jack,

Interesting link.

The paper offered was a model of terse reporting, sticking only with
the facts as best they could come by them, and little in the way of
overextending themselves with fanciful interpretations. The averages
were what they found for themselves, not abstracted and generalized to
the world at large.

I would suggest that they also made some cogent observations about the
soil structure that goes beyond myths and software passing as the new
age equivalent of old wive's tales. I would further observe that
making a declaration of what the resistance of ONE electrode is, is
farcical in the extreme. It would take two to tango and with that
second one added to measure the first, problems abound!

Especially notable is the 10 fold variation in reported electrode
resistance over a 4 year period, and the 10 fold variation of
electrode resistance within a survey group. Such an error range
easily eclipses what is taken on faith as "average ground." And then
we have to ask ourselves that embarrassing question, just how does the
mud in my backyard compare to "average?"

Your comments on
That means as close to
equipotential as possible, and it does not assume a good ground, or even any
ground at all in certain cases.
translate with fungible results to RF for the same reason. No one
here knows what quality ground they live over (really! to one skin
depth at HF?).

I would still like to know how many radials Reggie needs for his
several KOhm mud in his garden. No, I take that back, what I want to
know is what parameters he puts into the software that predicts the
number of radials - and why would it matter?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter"
wrote:

http://www.cpccorp.com/deep.htm

See the data in that
paper above for some sample resistance measurements which they consider
"average"

Hi Jack,

Interesting link.

The paper offered was a model of terse reporting, sticking only with
the facts as best they could come by them, and little in the way of
overextending themselves with fanciful interpretations. The averages
were what they found for themselves, not abstracted and generalized to
the world at large.

I would suggest that they also made some cogent observations about the
soil structure that goes beyond myths and software passing as the new
age equivalent of old wive's tales. I would further observe that
making a declaration of what the resistance of ONE electrode is, is
farcical in the extreme. It would take two to tango and with that
second one added to measure the first, problems abound!

Especially notable is the 10 fold variation in reported electrode
resistance over a 4 year period, and the 10 fold variation of
electrode resistance within a survey group. Such an error range
easily eclipses what is taken on faith as "average ground." And then
we have to ask ourselves that embarrassing question, just how does the
mud in my backyard compare to "average?"

Your comments on
That means as close to
equipotential as possible, and it does not assume a good ground, or even
any
ground at all in certain cases.
translate with fungible results to RF for the same reason. No one
here knows what quality ground they live over (really! to one skin
depth at HF?).

I would still like to know how many radials Reggie needs for his
several KOhm mud in his garden. No, I take that back, what I want to
know is what parameters he puts into the software that predicts the
number of radials - and why would it matter?

they 'why' is the real question as there are several reasons to design a
'ground' and each of them has different requirements. a few examples with
different needs:
1. home electrical safety ground.
2. electrical substation ground.
3. hv transmission line ground for step or touch potential.
4. hv transmission line ground for lightning protection.
5. building ground for lightning protection.
6. building ground for rf isolation
7. vertical antenna ground for rf return
these are all very different problems requiring very different solutions. i
write software, part of which helps design grounds for hv transmission line
structures. the theory and practice in this area is quite different from
that used to design any of the other types (except maybe for small buildings
requiring lightning protection). And some of the extensive testing we have
done on the physics of the problem shows that the ground reacts quite
differently from what most people expect when trying to dissipate lightning
transients. i wouldn't use my software to design a ground for my station,
though i did use some of the results of our tests to convince myself that
what i did do would be adequate. Nor would i take any one other program as
gospel when designing a ground for any particular type of installation.
indeed at my station i have several different types of 'ground' systems,
raised radials under elevated verticals, wire mesh mats on the ground under
elevated verticals, ground rods at towers and service entrances, ufer
grounds in foundations, perimeter ground around the house, each for a
slightly different purpose and no one good enough for all the jobs that need
to be done. Some help with rf radiation from antennas, some are lightning
protection, and some are for ac safety. and they can't be interchanged in
most cases... and some of them would not fit most layman's definition of
what a 'ground' even is.

On Thu, 9 Sep 2004 22:16:35 +0000 (UTC), "Reg Edwards"
wrote:

|I am not very familiar with USA power-grounding regulations and they
|probably vary from state to state. But I am under the impression that in
|some simple circumstances, perhaps domestic, a single ground rod is
|considered adequate for safety purposes.
|
|Under similar circumstances a maximum ground electrode resistance ( whatever
|its construction ) of 50 ohms is specified.
|
|A 'standard' ground rod is 8 feet long and 1 inch in diameter.
|
|An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec?
|
|The calculated resistance of a single standard rod in average soil is 194
|ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE
|shelves. There ought to be greater use made of it. )

I responded to this in more detail but the post never came through.
So more quickly this time see:

http://www.usda.gov/rus/telecom/publ...s/1751f802.pdf

[snip]

Roy Lewallen wrote:
Jimmie wrote:


Should re read what I write sometimes. I was refering to using the water
pipe as the sole ground for your electrical system. This used to be a
common
thing and pemissable by the NEC, not sure if it still is.


When I replaced my service in 1975, a water pipe ground (which is all my
1952 house had) wasn't sufficient to satisfy the NEC, so I had to add a
ground rod. So the NEC hasn't permitted a water pipe ground as the sole
ground for at least 29 years. It apparently was permissible in 1952.

Roy Lewallen, W7EL

And I had a friend, had home in Springfield Or., was built during the WAR!
Home was plummed with (If you can believe this) Electrical Conduit! Apparently,
because of the shortage of materials, this met code then! Stuff finally rotted
out, around 1971-- remember him useing his vacation to replum the house!
And I had one , in K.Falls, OR was built as old farm house, with steel pipe,
that started leaking- electrolysis was rapidly eating it- replaced with Copper.
Was curious about the UNIONS used on it-- turns out that those are INSULATED JOINTS!
Plumber said had Copper pipes eating out in as little as 3-5 years, before they were
available, with them expected 25-30 years, before the pipe gives out! As running
current thru a pipe with an insulated connection is worthless as a ground, and even
current flowing thru a copper pipe, is hazardious to its health, don't think would
recommend this tactic if you want a good ground. Jim NN7K