On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote:
[snip]
|In industrial situations, I have had to deal with ground loop
|problems, which are a PITA to find. Do your grounding correctly, and
|you will be safer, and have an easier time of it.

You should have seen the problems I had when I had the house
electricians wiring up an r-f shielded room. Trying to convince them
that they had to run just *one* ground wire from a single point on the
room to a building ground and not the service entrance ground *and*
that the wire couldn't be bare and laying on the sprinkler system
piping, the A/C ducts and electrical conduit in the overhead.

Then fighting off the fire department guys that insisted that they
were going to run a pipe into the room for sprinklers.

On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart
wrote:

On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote:
[snip]
|In industrial situations, I have had to deal with ground loop
|problems, which are a PITA to find. Do your grounding correctly, and
|you will be safer, and have an easier time of it.

You should have seen the problems I had when I had the house
electricians wiring up an r-f shielded room. Trying to convince them
that they had to run just *one* ground wire from a single point on the
room to a building ground and not the service entrance ground *and*
that the wire couldn't be bare and laying on the sprinkler system
piping, the A/C ducts and electrical conduit in the overhead.

Then fighting off the fire department guys that insisted that they
were going to run a pipe into the room for sprinklers.

Most licensed electricians (in theory all of them, but I'll leave
that) have a good understanding of issues related to DC and 60 Hz AC,
voltages up to 480, currents up to 100 A.

Once you get to higher frequencies, including RF, or to serious
voltages or currents, the number of people who really understand drops
off rather quickly, unfortunately as the potential problems and
dangers increase.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart wrote:

On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote:
[snip]
|In industrial situations, I have had to deal with ground loop
|problems, which are a PITA to find. Do your grounding correctly, and
|you will be safer, and have an easier time of it.

You should have seen the problems I had when I had the house
electricians wiring up an r-f shielded room. Trying to convince them
that they had to run just *one* ground wire from a single point on the
room to a building ground and not the service entrance ground *and*
that the wire couldn't be bare and laying on the sprinkler system
piping, the A/C ducts and electrical conduit in the overhead.

Then fighting off the fire department guys that insisted that they
were going to run a pipe into the room for sprinklers.

Apparently the electricians only knowledge of 'loop' was in 'loophole'.

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

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

On Thu, 09 Sep 2004 17:04:08 GMT, Walter Maxwell wrote:

|On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart wrote:
|
|On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote:
|[snip]
||In industrial situations, I have had to deal with ground loop
||problems, which are a PITA to find. Do your grounding correctly, and
||you will be safer, and have an easier time of it.
|
|You should have seen the problems I had when I had the house
|electricians wiring up an r-f shielded room. Trying to convince them
|that they had to run just *one* ground wire from a single point on the
|room to a building ground and not the service entrance ground *and*
|that the wire couldn't be bare and laying on the sprinkler system
|piping, the A/C ducts and electrical conduit in the overhead.
|
|Then fighting off the fire department guys that insisted that they
|were going to run a pipe into the room for sprinklers.
|
|Apparently the electricians only knowledge of 'loop' was in 'loophole'.

Yep. To elaborate. The building (100,000 sq ft) was constructed of
tip-up concrete exterior walls and steel columns and roof trusses. A
few of the columns, were dedicated ground points, complete with copper
plates for wire attachement. They were bonded to the steel rebar grid
in the concrete slab-on-grade floor.

All of the A/C conductors into the room, neutral included, ran through
some real hefty line filters that were on the outside of the room with
feedthrus into a distribution box inside. On top of the room was a
single copper stud for ground connection.

As I said earlier, the electricians wanted to ground the room with the
usual A/C distribution safety ground wire. When I said no, they
needed to go to the nearest column ground, they ran a 6 AWG bare
copper wire to the grounding plate. Of course the wire was in contact
with everything it contacted.

So when I saw this I said no, you have to run an insulated wire. So
the next iteration was a single green wire. I said no, some bozo
plumber (I shouldn't say this, my brother's a plumber) or HVAC guy
will be up there working and the wire will be in the way and they'll
cut it and my room with be a 100 or so V above ground due to all of
the capacitors in the filters. I finally got my insulated wire in
conduit.

Then the HVAC guys wanted to run a steel duct to the room. Noooo, use
an insulated collar and give me a pneumatic thermostat.

Then as mentioned earlier, it was the fire department. They saw all
of the handy pipes running through my feedthru panel (actually
waveguide below cutoff feedthrus) and said we can just plumb in the
water through one of these. Nooo, can't have a metallic connection.
So they say, they can use a dielectric union. Nooo, the water in
those pipes hasn't moved in 20 years and is primarily rust.

When they started talking about halon I said that my widow was going
to have a real good time with the millions she would get from the
lawsuit. They decided that the regular sprinkler system above the
shielded room was okay afterall.

"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