Earthing related questions

Sun Mar 28, 2010 12:23 am   

I was reading this article at: http://www.electronics-tutorials.com/basics/earth-dangers.htm

I have a couple of questions regarding this. I'll ask my question
after quoting the portion my question is related to.

1. "A further earth wire leads off to the water service and, in the
case of more modern homes now, a separate earth stake driven into the
ground."

Why does a earth wire lead off to the water service? What has water
service got to do with earth wire? Also, what exactly is meant by
water service here? Could someone please help me in visualizing? Is it
like they expose the earth wire to stored water?

2. "Taking the case where no earth stake exists, if the main neutral
conductor coming into the house is interrupted (and often can be for a
variety of reasons) then the only return path for electrical
continuity is the earthing system, down through the water service, out
into the street and back up through EVERYBODY'S water service / earth
system."

How does the earth wire act as the return path. Let us take a room
heater for example. The live wire would be connected to one end of the
heating element and the neutral wire would be connected to the other
end of the element. The earth wire would perhaps be connected to any
metal in the body of the heater to ensure that in case the live wire
comes in touch with the body of the heater, it doesn't induce an
electric shock to the user who happens to touch the body. So, the
earth wire is not connected to the heating element at all.

So, if the neutral wire is broken, there is absolutely no return path.
How does the earth wire become the return path in this case?


3. "How do I know a water service is live? Standard procedure (for
those who follow rules and procedures - idiots don't) is to first
connect, by way of proper earth clamp, an insulated earth wire of
standard 4 mm size to the water service as it emerges from the water
main. This cable is then run out to the meter box for connection to
the neutral link."

What is "water main"? Where exactly is the earth wire connected at the
water service's end?

A final question about this Usenet group. Is this the right place to
ask these questions? Why posting is no longer allowed in
sci.electronics?

Sun Mar 28, 2010 12:23 am   

Disc Magnet wrote:

So dont think that you will get a reliable earth contact
that way.
However, connecting anything metallic(heating, concrete skeleton
metal, any metal in the bathroom, your (metal)watertubes, etc ,
to a reliable grounding rod , is fine.
Just dont rely on the water service as a provider for ground.
Also check at the entry point of the wiring entering your
house, in our country (Netherlands) there is a reliable ground
connection supplied by the electricity company.

Sun Mar 28, 2010 12:51 am   

Disc Magnet wrote:


Water supply generally uses metal pipe.. which is in the ground deep
and makes for a good conductor, since it is coming in contact with a lot
of ground.. The water main is just the main pipe that enters your home
in some secure place where it's protected from cold weather to prevent
freezing..
Being underground x number of feet, protects it from this problem..

If for some reason you lose the noodle from the pole and you have a
ground problem with one of your appliances, You can have issues.!

Sun Mar 28, 2010 7:28 am   

On Sat, 27 Mar 2010 15:23:38 -0700 (PDT), Disc Magnet
<discmagnet_at_gmail.com> wrote:




The important point is right in the beginning of the article


Take a look at http://en.wikipedia.org/wiki/Earthing_system and
especially about the TN-C-S picture. In addition for the three phases
L1, L2 and L3, there is also a combined Protective Earth/Neutral (PEN)
wire from the transformer to the house. At the main distribution panel
(or whatever you call it in different countries), the PEN is split
into Protective Earth (PE) and Neutral (N) wires, which are kept
separate inside the house.

In normal situations only the N conductor will carry some current but
no current will flow in the PE conductor and all PE terminals in the
house will be at the same potential (the potential of the PEN to PE/N
split point). An isolation fault in a load device will drive a very
large current into the PE conductor and then into the PEN conductor
and finally blow the fuse in the corresponding live line.

Now assuming that every load device is working OK, but the loads on
the phases are unequal, so some current is flowing from the house to
the transformer through the PEN wire. Assuming the PEN wire is broken,
the potential of all the in house PE and N conductors will float to
some potential between the phases, depending of the size of the loads.
In a single phase system, the PE and N conductors will float to the
full line voltage. If there are truly grounded objects, such as
water/gass pipes and someone touches it and the case of an equipment
is floating, up to the full mains voltage would be across the person.

To avoid this, a separate grounding electrode is used at each house.

Notice that in the TN-C-S picture, the N star point of the transformer
is connected to a grounding electrode at the transformer (as well as
to the PEN line to the consumer).

When the PEN line between the transformer and consumer is broken, but
both the transformer as well as the consumer earthing electrodes are
intact, a current will flow through the earth to the transformer
neutral point, thus the PE and N wires inside the house do not float
freely at high and dangerous levels, but will remain in safe levels
for humans (but not necessary for equipment).

Connecting the PEN to PE/N split point to the water system serves two
purposes, as long as metallic pipes are used, the pipes will function
as additional ground electrodes but it also functions as equipotential
bonding
http://en.wikipedia.org/wiki/Electrical_bonding#Equipotential_bonding

In practice, the grounding resistance can be quite high (several ohms)
in a dry sandy environment, the potential can still float to
dangerous levels.

By connecting all the in house PE and N wires, the incoming PEN wire,
the water, gas, central heating pipes as well as antenna frame earth
as well as the actual grounding electrode into a common bar,
everything within the house will float at similar potentials, thus
there is not a serious risk of touching the water pipe and an earthed
device, even when both the PEN wire and the grounding electrode are
broken or the grounding resistance is high.