On 10/8/2012 3:42 PM, HeyBub wrote:
bud-- wrote:
Perhaps this will explain:
"You've probably seen project requirements that call for the
grounding of piping systems and exposed structural steel. Those
requirements, although well intended, miss the mark. The stated
intention of such requirements is nearly always the removal of
dangerous voltage on specific types of metal parts in the event of a
ground fault. These metal parts include exposed structural steel
members, electrically conductive metal water piping systems, metal
sprinkler piping, metal gas piping, and other metal piping systems.
But these requirements fail to make that intention a reality. That's
because you remove dangerous voltage on metal parts through bonding,
not through grounding."
No source.
Sorry. I thought the material was righteous on its face. Evidently not. See:
"Grounding vs. Bonding - Part 10 of 12"
http://ecmweb.com/bonding-amp-ground...ing-part-10-12
You edited out:
"I am not fond of the term "grounding" because you may be talking about
'bonding' or 'earthing'.
Your quote has that problem. (The NEC has started to clarify which use
is intended.) "
Looking at the article that appears to be the problem. The source talks
about "grounding". What does the source mean by "grounding"? Might mean
connecting branch circuit ground wire (which is how gas pipe is
"grounded", at least for residential). Might mean just earthing.
Something else? Water pipe and structural steel do need to be "bonded".
That is not a problem, except that structural steel (usually) and metal
water service pipe (always) must be used as an earthing electrode where
there is an electrical service in the building. And if connected as an
earthing electrode the metal is also "bonded".
The source incorrectly shows a "bonding" connection from the service to
a metal water pipe but the code reference (table 250.66) clearly shows
this is a connection as an earthing electrode. "Bonding" rules are
different.
It should have been a good source. It was partly correct, but did not
(in this article) cover earthing electrodes. The NEC chapter on
grounding is probably the most confusing one that is commonly used. IMHO
a lot of that is confusion over what "grounding" is supposed to do in a
particular instance. That is why I use "earthing", where appropriate.
The NEC has 3 electrodes that are *required* to be used as earthing
electrodes (where present).
One is metal water service pipe (10 ft...).
Another, in general, is structural steel (because of its connection
into the rebar systems in the concrete foundation).
Your source is incorrect - water pipe and structural steel *must* (in
general) be used as earthing electrodes.
If they are connected as earthing electrodes they are also "bonded".
"Your source is incorrect..."
Giggle
Oh how funny
and
"The NEC (section 250-81 through 250-83) requires that the
electrical system connected to all of the following, if available
for grounding purposes: * metal frame of building
* concrete encased electrode (rod, pipe, plate, braided wire)
* ground ring and
* metallic water pipe with 10 lineal feet in contact with earth
The correct list has electodes that may already be present in a
building and does not include ground rings and everything after
"concrete encased electrode".
The NEC has noted that metal piping will corrode over time and
possibly lose its continuity with the soil (i.e. ground) or be
replaced by plastic pipe. Accordingly, should this occur, the NEC
has mandated the 3 other paths to ground be utilized."
Cite for corrode.
Cite where water pipe has worse corrosion problems that ground rods.
Does not exactly satisfy your request, but of interest:
"The NEC has noted that metal piping will corrode over time and possibly
lose its continuity with the soil (i.e. ground) or be replaced by plastic
pipe. Accordingly, should this occur, the NEC has mandated the 3 other paths
to ground be utilized."
http://www.ct.gov/dph/lib/dph/enviro..._Necessity.pdf
Your source doesn't want the water pipe used as an earthing electrode,
but has no problem with "bonding" it to the electrical service. If you
do that the water pipe will also, in fact, function as an earthing
electrode (with all the awful consequence the source supposes). That is
probably why the NEC "bonding" rules are similar to the rules for using
water pipe as an earthing electrode.
The NEC has NOT mandated that "3 other paths" to earth be utilized.
Yes it has. (See above)
Your source is wrong.
There are 2 separate issues.
One is water pipe. The NEC has required a *single* "supplemental"
electrode since 1978 (as dpb writes) and since long before that in some
cases. It does not require 3.
Second is that the NEC now requires 3 specific electrodes be part of the
earthing system, if present.
Your source rather stupidly says the 3 paths are required as the
supplemental electrode for metal water service pipe when one of the
paths is metal water service pipe. And the other 2 may not exist.
In other words, attaching a metal water pipe to an earth ground is
used to protect the user from the plumbing, not to provide a ground
for the electrical system. Using metal water pipe as an electrical
ground is insufficient.
The requirement to use water pipes as an earthing electrode is in a
section on the earthing system and the electrodes to be used.
It is in your list of required earthing electrodes, above.
You have bullsiht information and are using a bullsiht source.
(What a surprise.)
I assume your "non-bull****" source is your own dim remembrance of things
past.
My "non-bull****" source is the National Electrical Code.
(Apologies if this double posts.)