"w_tom" wrote in message
...

Attitude of code is that water pipe is not sufficient as the
primary or reliable earth ground connection.

That's just not true, Tom. An underground metal water pipe is indeed a very
good grounding electrode. Why then does NEC (2002)Section 250.30(4)
_specifically_ require that an underground water pipe (and/or structural
steel) be used as the primary grounding electrode? Why then does the NEC
allow _made_ grounding electrodes (ground rods,etc) ONLY when a water ground
or structural steel is not available?

A separate
ground rod (or something equivalent) is required even if water
pipe earthing is available.


The ONLY reason that a ground rod is required by NEC to _supplement_ a water
ground is because of the distinct possibility that the metal water pipe may
be replaced by the water co.......leaving the system with no ground at all.
While a single ground rod is not the best ground, it's _certainly_ better
than none at all.


Other incoming utilities will use
that ground rod as central earth ground; not water pipe.


Again, just not true. The other utilities will grab on to any ground that
they can find. The NEC indeed requires that the electric service have
provision for same......even if it's just a bare #6 hanging out of the
bottom of the electric panel. There is not such thing as "central earth
ground" as you describe it.......and is in fact ludicrous to think that a
single ground rod is the "central earth ground." A single ground rod is
about the worst possible grounding electrode permitted by NEC.......it just
can't dissipate near as many electrons in a given time time as compared to a
water ground, ufer, structural steel, or a ground ring. In fact, it if you
try to dump all that on a single ground rod it will become a choke. That's
why, when installing a single ground rod (only) as a supplement to a better
ground, such as a water ground, that the wire to the an _individual_ ground
rod, REGARDLESS of the size of service only needs to be a #6 wire (per
NEC)........the ground rod just won't dissipate any more electrons than the
#6 can handle.


Connection to water pipe is supplemental earthing to new
installations.

No, it is _not_. It is the _primary_ grounding electrode, if available.
Problem is, these days plastic pipe is used. Any interior metal water
piping is connected to the neutral busbar to clear ground-faults should they
become energized.

Connection to one or multiple earth ground rod
(or whatever else you use for the earthing system), all at
same point, becomes single point earth ground.

No, connection (bonding) of multiple grounding electrodes forms a _single_
grounding electrode _system_. If you want to call something "a central
earth ground" the service entrance neutral busbar would be a more accurate
description. Even microwave towers have at least 100 or more Cad Welds
bonding every possible piece of metal and ground together. Where is the
"central earth ground" on that? There is _no_ single grounding point. If
you're referring to a single grounding connection point on a micowave tower
before all cables enter the building, then the corresponding single
grounding connection point on a house is basically the service equipment
neutral busbar. And if you want to start rambling about differential and
common mode surges......then you should at least recognize that, indeed, the
service entrance neutral busbar is _where_ the neutral and the equipment
grounding conductors are bonded together.......and _think_ about _that_
before you respond.


Everything
earths to multiple ground rods at same point.

Yeah, like the neutral busbar in the service equipment! It's not a radar
station, Tom.


Even the
television aerial should make some connection to that single
point earth ground before entering a building even though the
aerial itself has a direct connection to a separate ground rod
- to fully optimize earthing for surge protection. These
exceed code requirements to make a superior protection
'system'.

That connection to water pipe is primarily to remove
currents from pipes - for human safety.


No, the primary purpose of a metal underground water pipe is to ground the
electric system.


Same safety reason is
why hot water pipes would also be grounded to panel ground.
If water pipe is also being used

Code requires a second ground rod if the first does not
measure less than 25 ohms. If second rod does not make less
than 25 ohms, then a third rod is not required - by code.
Code is not optimized for effective surge protection.


THAT, I will concur. With more and more plastic being used these days, it's
very difficult to obtain a decent electric system ground. It would not be
much of a hardship on electrical contractors for the NEC to require a Ufer
(concrete-encased) grounding system......they just need to be there before
the concrete gets poured. Make it a requirement to get the OK to pour, just
like bug spray is required in most areas.


If
earth is so non-conductive as to not supply less than 25 ohms,
then a more serious earthing system should be installed such
as halo ground, plate electrodes, or Ufer grounding. One rod
will make a minimally sufficient earthing connection in most
cases. Two rods will make every 'whole house' protector more
effective. The most important component in a surge
protection 'system' is its earth ground.


Totally agree.


Earthing and
distance of wire to that central earth ground will often be
the 'choke point' for system effectiveness. Additional money
spent on surge protection often is best spent on enhancing the
single point earth ground.

Code does not define how that earth resistance is to be
measured. Most locations will get less than 25 ohms with only
one ground rod. However, considering how important that
earthing system is also for transistor safety, then a second
rod is cheap insurance. Utility will install massive
grounding networks underneath a substation and still obtain
resistance on the order of 2 ohms. The first rod will lower
resistance. Every additional rod will provide less
improvement.


'nuther Bob wrote:
On Sat, 12 Jul 2003 03:22:50 GMT, "Mark or Sue"
wrote:
To summarize, if you have a metal water pipe that is in contact
with the earth for 10 feet or more, you MUST use it as your
primary grounding electrode.

WOuld "MUST" still apply if the proper attachment location to the
water pipe is 35 feet from the panel ? Or would the code then
prefer two grounding rods ?