Some comments regarding US NEC requirements for grounds. You locale may
differ.
Your main service entrance must be "grounded" to the following grounding
electrodes, if present:
1 - Cold water pipe within 5 ft of it's entry to the house, IF at least
10 feet of the underground portion is metallic.
2 - The building steel frame if any.
3 - A "UFER" ground in newly constructed buildings, consisting of a
connection to the rebar in the concrete foundation or wire in the
concrete instead of rebar. Don't remember the exact lengths req'd
without my code book in hand.
4 - If #2 or #3 don't exist, you need to add a ground rod to supplement
the cold water pipe connection. The rod's resistance must be less than
25 ohms. If not, you need to add a second rod. Some people just put in
two rods and be done with it as the second rod eliminates the need for a
resistance measurement.
As far as the NEC is concerned, these grounding electrodes are primarily
for lightning protection. In some cases they help stabilize the voltage
of the system, i.e. no floating neutral because of the neutral-ground
bond at the main panel (and only at the main panel). They are NOT there
for overcurrent protection and related safety concerns.
The NEC actually mentions that the earth may never be used as a safety
ground, or current path of any kind.
Before the 2008 NEC you could run power to a second building without a
ground wire, and reestablish ground using the above electrodes at the
second building, IF there were no other ground return paths between
buildings. As of the 2008 NEC a ground conductor must be run in the
feeder to the second building, in new construction. Existing
installations are exempt.
You must "bond" all communication systems grounds to your service
ground, i.e. grounds from amateur, CATV, telephone, satellite etc. to
eliminate possible potential (voltage) differences between systems.
Just FYI - 73
Steve Kurtzman, P.E. W7SJK
> Date: Wed, 26 Jan 2011 12:29:05 -0800
> From: "KD7JYK DM09"<kd7jyk@earthlink.net>
> Subject: [RFI] CHECK your grounds.
> To: "RFI RFI"<rfi@contesting.com>
> Message-ID:<019801cbbd97$b1532a40$55a4f604@mainframe>
> Content-Type: text/plain; charset="iso-8859-1"
>
> We have three power poles on our land bringing in 220VAC at 200 Amperes.
>
> Ther first pole just carriedspower wires, here it splits, like a Y to two
> other poles.
>
> Pole #1 only feeds a water pump through a subpanel with breakers. This pole
> has a new electronic power meter. This was installed in 1975.
>
> Pole #2 has a mechanical meter and feeds the house from here, underground
> about 250' to a subpanel with circuit breakers that distribute power through
> out the dwelling. This was installed in 1981.
>
> Pole #1 has NO ground. There is a severely corroded mass of metal that
> resembles a ground rod and clamp. There is no wire to the subpanel.
>
> Pole #2 has has an oxidized ground rod and clamp partially covered in bird
> droppings. The ground wire, which may or may not actually be connected to
> the household electrical system- I have yet to check, brushes against the
> ground clamp, then makes three loops around the ground rod ranging from 1/4"
> to 1/2" around the rod. This was discovered under a mass of wet leaves and
> other debris.
>
> Back to pole #1 which feeds our water pump... I discovered many years ago
> that the WATER, traveling some 150' up 1-1/4" PVC pipe was the actual
> neutral/ground line for our 200 amp curcuit in the house! Talk about HOT
> water! I have since fixed this.
>
> I have taken photos of our electrical "grounds". These are an insane
> disaster! They are available to those that would like to see them, I
> suggest people put them on their websites and tell other about them.
>
> Kurt
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