Jim Redelfs wrote:
In article
,
Andy wrote:

I was told that the Demark box MUST be installed at the
electrical service entrance and the ground wire attached
to the service entrance ground rod...

That is correct and has been required by code for many years.

Specifically, telco and CATV services must be bonded to the MGN
(Multi-Grounded Neutral) wire of the premise using the SHORTEST length
of wire as is practical.
..
The NEC requires a wire "short as practical" with a max length of 20 ft
from phone/cable entry protectors to the power
grounding-electrode-system. (For 1 and 2 family dwellings, if the wire
has to be over 20 ft it can be longer with a ground rod near the entry
protector.) For phones, even 20 ft can be too long.

Phone people like Jim are likely well aware of this. Cable people,
particularly contractors, are more of a problem.
..

This provides the best "balanced potential" in grounding. It is said
that such practice lowers the chance that, in a direct lightening
strike, the charge will "leap" from a phone or CATV jack to an
electrical outlet. I have seen that sort of damage. It's impressive.
..
Can’t imagine.

With a lot of electronic equipment connected to both power and
phone/cable, you want to minimize the voltage between power and
phone/cable wires. Insurance information suggests the most common damage
to electronic equipment is from high voltages between power and
phone/cable wires. Having a *short* wire from phone/cable entry
protectors to the ground at the power service minimizes the voltage
between power and phone/cable wires. The power service is the magic
point because neutral and ground are bonded at that point.

With a strong surge current to earth the "ground" at the building can
rise thousands of volts above 'absolute' ground. You want the power and
phone and cable grounds to rise together.

Art writes about high voltage between power and signal wires. There is
an illustration of a cable ground wire that is too long starting pdf
page 40 in an excellent IEEE guide on surges:
http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf

--
bud--

..

I suggested just putting in another ground rod at the
alternate location instead. I was told this was not allowed
--- the Demark box MUST go at the meter service entrance.

For the BEST service and the best protection from transient spikes
(surges), you WANT the SNI/D at the electric service entrance.

For the first, hundred years or so, telephone service was brought into a
premise at virtually ANY location. They often used a ground rod (4-ft
galvanized!) instead of a water pipe for bonding.

The proliferation of electronic devices (MUCH more susceptible to surge
damage than the old phones) connected to the network made common bonding
imperative.