"bud--" wrote in message
eb.com...
On 11/15/2012 6:02 PM, (PeteCresswell) wrote:
I tried this in misc.rural, and got a recommendation to try it
here.
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Been quite awhile since I started wondering what it was with the
"Building Wiring Fault" lights on my UPS'.

In doing some homework prior to getting a generator transfer
switch installed, it became apparent that houses need tb
"Grounded" - and the typical ground is one or more copper rods
pounded into the ground and then attached to a (neutral?) wire in
the breaker panel.

I assume this is the US, and there is an electrical code that is
substantially the same as the National Electrical Code.

There are several major elements to the building "ground" system.

One is a bond between the neutral and service panel enclosure. The
enclosure is the basic system "ground". The bond may be a visible strap.
It can be a screw that just looks like a mounting screw for the neutral
bar. This bonding is critical for tripping breakers when there is a short
from, for instance, the hot wire in a drill to the metal drill case that
is connected to the ground pin at a grounded receptacle.

Another element is one or more earthing electrodes. They are not for
tripping breakers. They keep the building "ground" at approximately earth
potential, and keep the hot and neutral wires at a reasonable potential
with respect to earth.

The third element is grounding conductors that go with the branch circuit
and connect to the ground terminal on receptacles. The grounding conductor
can be a bare or green wire, or it can be the metal of the wiring system.

I would understand "building wiring fault" to mean that there is no branch
circuit grounding conductor or there is no neutral-ground bond at the
panel. The UPS has no way of telling if the building "ground" is earthed.


This house is a split-level, crawl space but no basement, built
in the fifties and I am unable to find anything that even looks
like a ground.

One reason for no ground might be what the house is built on: a
shale ridge. The builder scooped a notch out of a hillside,
sold the topsoil, and built this house on the notch. Go down
about 4", and you hit shale that is so solid that you need an air
hammer or a breaker bar and lots of time to get through - as in 3
days with a breaker bar and a tin cup to make 2 4" wide 28" deep
holes for a boat rack I put in last year.

Realistically, we've been in this house for 30+ years and never
lost an appliance to electrical surge... but still... there's got
tb good reasons for grounding.

That being said, I'm exploring after-the-fact methods.

The obvious is the copper pipe that water comes in on: buried
several feet deep and running a good 30' to the main under the
street. Seems like this was SOP until some time in recent
history when it was deemed inadequate.

In the 50s the water pipe would have been entirely adequate as an earthing
electrode. A metal water service pipe and metal municipal water system is
still the best earthing electrode you will find at a house. Relatively
recently a "supplemental" electrode has been required because the metal
water service pipe can be replace by plastic in the future. The the N-G
bonded service bar should have been connected to your water pipe (#6 wire
is usually used for 100A services), and a bonding wire should have been
connected across the water meter. The code now wants the wire from the
panel to connect within 5 feet of where the water pipe enters the house.
This will be your best earthing electrode.


The second thing that comes up is a "Ufer" ground wherein the
ground wire is tied to rebar in the house's foundation. I can
find a lot of articles on the techniques of doing this in new
construction, but nothing about retrofits.

This is the next best earthing electrode, but is only practical to add
before the foundation is poured.


The third approach seems tb lateral: long trenches in the yard
with the grounding medium layed in the trench. Seems
impractical to me bc the standard calls for 30" deep...

Has anybody been he retrofitting a ground system to a house
built on shale or rock?

Ground rods can be driven at an angle or even installed flat. Ground rods
are about the worst electrode.

Ask the electrical inspector what they would recommend.

Great discussion and useful information. It wasn't a retrofit, but I do
have thick layers of sandstone about 18 in. below grade (no basement!) and
so made sure that the water and gas piping in the house, now about 10 years
old, is bonded to the copper water supply pipe going to the street. The gas
supply pipe is plastic. The water pipe is buried in a trench about 3 feet
deep chipped out of the rock and back filled with sand and top soil.

The main panel is connected to a ground electrode which the contractor made
by drilling down into the stone and putting in a copper rod. I've checked
for a voltage difference a few times between the panel and the incoming
copper water pipe and it measured zero on the most sensitive setting of the
multi-meter. Probably that's because the top soil is usually moist to wet
since rain water doesn't sink into the sandstone, but slowly moves
horizontally keeping the region around the top soil and stone conductive.

The incoming water pipe and ground electrode are about 15 feet apart with no
direct bond. Should there be one?

Tomsic