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wrote:
Chip C wrote:

I'm confident that my responses will draw at least as many flames as
your questions would.

Thank you for your detailed reply Chip. It is very helpful.

I am still a bit fuzzy about the ground bar and neutral bar being
'connected' at the service panel. Won't all electricity just goes to
the ground in that case? I know it sounds silly, but what's the
difference between connecting the ground/neutral at the panel vs
connecting them at the receptacle? a wire is a wire right?

I suspected the answer to "why only one ground/grouding rod" is
the big IF part in my post. Thank you for clearifying that part.

let me ask another (not a troll!) question, in many areas, redundancy
is good. if one fails, the other still works. isn't having two
properly done ground rods better than one? If one fails, then the
other should still work? having the code calling for one and only
grounding to be done at the service panel, then the whole system will
be depending on that grounding work correctly. The probability of one
fails is much higher than the probability of both fails right?

I mean redundancy is why I backup my data to CDRs.

So if I understand it correctly, the grounding for the satellite dish
for example, is to connect the metal part of the dish to the ground
bar in the main service panel via a proper ground wire? not to the
earth right under the satellite dish (or roof) which I can dug a hole
and bury the bare copper wire that came with my satellite install kit?
And the reason being the ground at the servie panel will most likely
provide less resistence than my bare wire?

Thanks again.

Raymond

Raymond

The biggest fallacy in the common understanding of electricity is that
electricity somehow seeks out the earth. That is simply untrue.
Current will flow from a point of higher voltage to a point of lower
voltage if there is a conductive path between them. Given a high enough
voltage almost anything will serve as that conductive path. Lightning
through the air is one example of this. For general public electrical
safety education purposes it is best to think of current as trying to
return to it's source rather than the earth. If one leg of the source
is grounded and the circuit is grounded at other points, as it is in the
US multi grounded neutral system, then the earth will carry part of the
current back to the source. Current does not take the path of least
resistance back to it's source it takes all available paths back to it's
source in proportion to the resistance of the available pathways.

In many main electrical panel enclosure cabinets; that are functioning
as the Service Disconnecting Means enclosure in homes; the neutral buss
bar and the Equipment Grounding (Bonding) buss are the same buss bar.
In some brands of panel, GE comes to mind, that buss bar can be divided
in half and used as two separate buss bars. In other brands, such as
SquareD, if you need a separate ground buss you add it using a buss bar
kit you purchase from the vender. The US NEC requires the neutral
conductor of the supply must be grounded to the earth somewhere between
the demarcation point; that separates your wiring and the utilities
wiring; and the neutral terminal of the service disconnecting means.
This connection is made to make the installation somewhat resistant to
the damage that would be caused by lightning and other high voltage
transient current flows. Lightning, you see, is indeed trying to return
to earth and the opposing atmospheric air mass because that is the
source of the current. The US NEC states it this way.

[Electrical systems that are grounded shall be connected to earth in a
manner that will limit the voltage imposed by lightning, line surges, or
unintentional contact with higher-voltage lines and that will stabilize
the voltage to earth during normal operation.

Non–current-carrying conductive materials enclosing electrical
conductors or equipment, or forming part of such equipment, shall be
connected to earth so as to limit the voltage to ground on these
materials.(copyright 2002 National Fire Protection Association]

So we ground electrical systems to limit the voltage to ground because
that reduces the likelihood of destructive current flows between the
systems components and ground or earth.

Grounding does not play much of a roll in the actual functioning of your
homes electrical system. Aircraft in flight have a perfectly functional
electrical system including regular AC outlets that can be used to power
electric shavers and sometimes passenger owned electronic devices such
as lap top computers. For ease of design, construction, and maintenance
such systems have to have a reference point that can be considered zero
volts. The aircraft's frame is used. Obviously we cannot ground
anything on an aircraft in flight but we still must bond all of the non
current carrying parts of the electrical system back to the source of
supply, just as we do in a buildings electrical system, and to the
aircrafts common point in this case the airframe.

This bonding; the term of art is presently equipment grounding but there
is a proposed amendment that will change this to equipment bonding; is
done to provide a low resistance return path back to the source for
current which has escaped the normal current carrying conductors thus
allowing it to complete it's circuit in a non dangerous and non
destructive manner. The US NEC describes the purpose of this deliberate
interconnection of all non current carrying parts of the electrical
system this way.

[Non–current-carrying conductive materials enclosing electrical
conductors or equipment, or forming part of such equipment, shall be
connected together and to the electrical supply source in a manner that
establishes an effective ground-fault current path.

Electrically conductive materials that are likely to become energized
shall be connected together and to the electrical supply source in a
manner that establishes an effective ground-fault current path.

Electrical equipment and wiring and other electrically conductive
material likely to become energized shall be installed in a manner that
creates a permanent, low-impedance circuit capable of safely carrying
the maximum ground-fault current likely to be imposed on it from any
point on the wiring system where a ground fault may occur to the
electrical supply source. The earth shall not be used as the sole
equipment grounding conductor or effective ground-fault current path.
(copyright 2002 National Fire Protection Association)]

So lets review what we are trying to do. We want to limit the voltage
to ground so as to avoid destructive and dangerous current flows between
the system and the earth. In North American practice the techniques
used to accomplish this are called grounding. We also want to provide a
low resistance pathway back to the source so that any escaped or faulted
current can return to the source in a non dangerous and non destructive
manner. Those techniques are called equipment grounding but soon to be
called bonding.

As to how many different ways you can ground the system the US NEC
requires that any of the electrodes in the list that are present on the
sight must be used to construct the grounding electrode system.

[If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used.

A metal underground water pipe in direct contact with the earth for 3.0
m (10 ft) or more (including any metal well casing effectively bonded to
the pipe) and electrically continuous (or made electrically continuous
by bonding around insulating joints or insulating pipe) to the points of
connection of the grounding electrode conductor and the bonding
conductors. Interior metal water piping located more than 1.52 m (5 ft)
from the point of entrance to the building shall not be used as a part
of the grounding electrode system or as a conductor to interconnect
electrodes that are part of the grounding electrode system.

The metal frame of the building or structure, where effectively grounded.

Concrete-Encased Electrode. An electrode encased by at least 50 mm (2
in.) of concrete, located within and near the bottom of a concrete
foundation or footing that is in direct contact with the earth,
consisting of at least 6.0 m (20 ft) of one or more bare or zinc
galvanized or other electrically conductive coated steel reinforcing
bars or rods of not less than 13 mm (½ in.) in diameter, or consisting
of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4
AWG. Reinforcing bars shall be permitted to be bonded together by the
usual steel tie wires or other effective means.

A ground ring encircling the building or structure, in direct contact
with the earth, consisting of at least 6.0 m (20 ft) of bare copper
conductor not smaller than 2 AWG.

Rod and pipe electrodes shall not be less than 2.5 m (8 ft) in length
and shall consist of the following materials.
(a) Electrodes of pipe or conduit shall not be smaller than metric
designator 21 (trade size 3/4) and, where of iron or steel, shall have
the outer surface galvanized or otherwise metal-coated for corrosion
protection.
(b) Electrodes of rods of iron or steel shall be at least 15.87 mm (5/8
in.) in diameter. Stainless steel rods less than 16 mm (5/8 in.) in
diameter, nonferrous rods, or their equivalent shall be listed and shall
not be less than 13 mm (1/2 in.) in diameter.

Plate Electrodes. Each plate electrode shall expose not less than 0.186
m2 (2 ft2) of surface to exterior soil. Electrodes of iron or steel
plates shall be at least 6.4 mm (1/4 in.) in thickness. Electrodes of
nonferrous metal shall be at least 1.5 mm (0.06 in.) in thickness.

Other local metal underground systems or structures such as piping
systems and underground tanks.(copyright 2002 National Fire Protection
Association)]

About your satellite dish. The reason that it is so important to bond
your satellite dish to the buildings electrical grounding electrode
system rather than to a separate isolated ground rod is that separate
ground points can have a difference of potential or voltage between
them. The higher that voltage is allowed to become the more likely a
dangerous or destructive current flow becomes. There is nothing wrong
with having a ground rod directly under the dish. I would in fact argue
that it would be best practice to install one there. The critical thing
is to bond the dishes rod to the rest of the grounding electrode system
so that they all behave electrically as a single electrode.

That is more than enough for one posting.
--
Tom H

"Can you skin Griz?

Well skin that one pilgrim and I'll bring you another."