Re: why ground an alarm panel.

[w_tom <w_tom1@xxxxxxxxxxx>]

  As posted earlier, the cold water pipe is no longer
sufficient as ground.  Copper wire to water pipe is for
'bonding' - to remove stray or dangerous currents from the
pipe.  NEC describes water pipe only as supplemental
earthing.  NEC lists what can be the only earthing electrode -
water pipe is not in that list.

  Other ground wires such as across 'cold to hot' at hot water
heater, across water meter, etc are for 'human safety'.  House
must be wired so that a plumber can break any pipe connection
and not affect electrical conductivity - human not endangered
by electrical shock.  This is a major change since the 1980s
when water pipes were acceptable for grounding.

  Furthermore, there exists no practicable way to measure or
test for proper grounds.  One can test for missing grounds,
but one cannot test for sufficient grounds.  Essential
connections for human safety must be installed so as to be
inspected.  Inspection being necessary to verify properly
installed grounds.  Codes sometimes are not clear or specific
about this.  But again, this concept should be intuitively
obvious - the purpose being human safety.

  Code does not demand two ground rods placed 6 feet apart.
But since 'few to no one' has equipment to meet code
requirements, then many will assume earthing is insufficient
and install the second rod.

  Reasons for panel directly connected to earthing electrode
is due to an electrical concept called impedance.  Things that
create too much impedance include splicing, sharp wire bends,
running wire inside metallic conduit, lead solder joints,
etc.  'Human safety' requires low resistance grounding.
'Transistor safety' requires low impedance grounding.

  BTW, if a wire is longer, then increasing wire gauge does
little to reduce wire 'impedance'.  Wire impedance is defined
more by wire length and less by wire diameter.  Notice how
this differs from another concept - wire 'resistance'.
Something wired with a low resistance connection may not also
be a low impedance connection.  Routing of that wire can even
make a significant difference for 'transistor safety'.

  Again review a previous post that included figures from
www.cinergy.com.   It demonstrates, for example, how to "run
to YOUR OWN supplementary electrode".  The concept, described
in that previous post yesterday (Wednesday), is called 'single
point'.  Installed for reasons, for example, that are similar
to eliminating hum from interconnected stereo components.

Bill wrote:
> FYI - A good electrical service grounding system has a cold water
> pipe ground, a separate ground wire from the main electrical
> panel going to two ground rods placed 6 ft. apart, a grounding
> jumper between the hot and cold water pipes at the water heater,
> and a grounding jumper connecting the in and out pipes at the
> water meter.