There's just too much bullshit, and not any answers worth replying to.
For instance, your claim that Part-68 specifies the grounding.
It doesn't. (Or at least I did not see it?)
See:
http://www.access.gpo.gov/nara/cfr/waisidx_07/47cfr68_07.html
To my reading, that information is contained within the document
specified by Rule 47CFR68.7(b)
In fact, I didn't see the word "ground" anywhere in the entire set of
rules.
Now, back to the questions / assumptions / whatever.
Michael only asked where that much arial cable was installed, I did
not read that as argumentative??
Anyway, those of us who KNOW, (and that includes Michael as I am aware
of his background having spoken to him by telephone) can attest
that:
Phones line protectors do not always work. No matter how good the
protection is, a direct strike can (and usually does) kill it.
The "problem" is most engineers don't truly know what a direct strike
is. What a lot of folks think is a direct strike is actually one that
is some distance away, even though there may still be a slight fault
current flowing in the Earth. Any ground conductor (ground rod,
etc..) that is driven into soil that is actively conducting a
lightning strike is not truly "ground", and is offering somewhat less
than optimal "protection", if indeed any protection at all. If you
care to know more: I refer you to any of the excellent texts by Martin
Uman. (University of Florida Press)
Whether under/above ground or copper / SLIC-fiber electronics, they
all suffer from this type of damage... eventually.
Generally, underground is better (geometry), and optics are better
(lack of conductivity).
As for Telco technology, most of the US (which is where we're
deploying the devices) is rather updated, but this is not universally
the case. For example, I know a handful of places that still have 5-
digit permissive dialing on an ESS-5 or earlier switch. And mostly
copper facilities.
Part 68 requires earthing per the National Electrical Code. NEC says
that phone line must be earthed by a wire of less than 20 feet. That
is for human safety. For surge protection, we both meet and exceed
that earthing requirement. For example, better surge protection means
that earthing wire is less than 10 feet AND is the same earth ground
used by every incoming wire.
When a phone line protector does not work, the human has foolishly
assumed the protector provides that protection. It does not for the
same reason that lightning rods are also only as effective as their
earth ground.
When protection fails, the study (by engineers, not by techs such as
Michael Terrell) starts with identifying a defective earth ground.
Again, what does Electrical Engineering Times discuss in an articles
entitled "Protecting Electrical Devices from Lightning Transients"?
Earth ground and connections to earth ground. Where popular myth is
common, somehow the protector will stop what three miles of sky could
not. Obviously not. Surge protection is about dissipating surge
energy where it causes no harm. Protector simply connects surge
energy into earth. Protectors that are too far from earth also
permits surges to find earth ground, destructively, via household
appliances.
You have stated that some "protectors do not always work." Of
course. The protectors are only connecting devices. Protection is
determines by the connection to and quality of earth ground.
The direct strike is when lightning strikes wires entering your
building. Effective surge protection earths that direct strike
without damage to the protector. Every phone wire entering the CO
from so many subscribers Is (was) copper. Why do telco switching
centers suffer typically 100 surges during every thunderstorm without
any damage. That CO has the same protector installed at your building
- and an even better earth ground.
Let's see what professionals do to eliminate surge damage. For
example, Orange County FL emergency response facilities suffered
damage from lightning. Any damage is unacceptable. So Orange County
fixed the only reason for their surge damage: earth ground.
http://www.psihq.com/AllCopper.htm
In Nebraska, a radio station suffered damage from lightning.
Finally, they decided to stop listening to myths; consulted a
professional. Well, the professional restored earth ground
disconnected by technicians who had listened to myths. And
professionals upgraded the earthing:
http://www.copper.org/applications/electrical/pq/casestudy/nebraska.html
First and foremost, the entire electrical system must be properly
installed according to NEC requirements. ...
It is absolutely imperative that all surge suppressors be grounded.
Or learn from another professional what an effective surge protector
does:
http://www.telebyteusa.com/primer/ch6.htm
Conceptually, lightning protection devices are switches to ground.
Once a threatening surge is detected, a lightning protection
device grounds the incoming signal connection point of the
equipment being protected. Thus, redirecting the threatening
surge on a path-of-least resistance (impedance) to ground
where it is absorbed.
Any lightning protection device must be composed of two
"subsystems," a switch which is essentially some type of
switching circuitry and a good ground connection-to allow
dissipation of the surge energy.
Same principles of surge protection apply to radio stations,
incoming AC electric, or telephone. Surges are earthed before
entering a building or will find destructive paths inside that
building. From another professional:
http://www.harvardrepeater.org/news/lightning.html
Well I assert, from personal and broadcast experience
spanning 30 years, that you can design a system that will
handle *direct lightning strikes* on a routine basis. It takes
some planning and careful layout, but it's not hard, nor is
it overly expensive. At WXIA-TV, my other job, we take
direct lightning strikes nearly every time there's a
thunderstorm. Our downtime from such strikes is almost
non-existant. The last time we went down from a strike,
it was due to a strike on the power company's lines
knocking *them* out, ...
Since my disasterous strike, I've been campaigning
vigorously to educate amateurs that you *can* avoid
damage from direct strikes. The belief that there's no
protection from direct strike damage is *myth*. ...
The keys to effective lightning protection are surprisingly
simple, and surprisingly less than obvious. Of course
you *must* have a single point ground system that
eliminates all ground loops. And you must present a low
*impedance* path for the energy to go. That's most
generally a low *inductance* path rather than just a low
ohm DC path.
A benchmark for surge protection is Polyphaser. Polyphaser makes a
protector that has no connection to earth ground. Why? Because
increased distance to earth means less protection. That Polyphaser
protector mounts ON earth ground - zero feet away. But again,
Polyphaser application notes are considered legendary by those who
learned the science rather than the many myths that were posted here
by others. What does Polyphaser discuss? Earth ground:
http://www.polyphaser.com/technical_notes.aspx
Anyone who knows or demands surge protection discuss earth ground.
Sun Microsystems Planning Guide for the Server Room (contrary to the
myths posted by others) also says what provides surge protection:
Section 6.4.7 Lightning Protection:
Lightning surges cannot be stopped, but they can be diverted.
The plans for the data center should be thoroughly reviewed to
identify any paths for surge entry into the data center. Surge
arrestors can be designed into the system to help mitigate the
potential for lightning damage within the data center. These
should divert the power of the surge by providing a path to
ground for the surge energy. ... It is also necessary to protect
against surges through the communications lines. The specific
design of the lightning protection system for the data center will
be dependent on the design of the building and utilities and
existing protection measures.
Surge protection is determined at the building level by earth ground
and having all utilities enter at a common service entrance. If the
building was constructed erroneously, a utility explains how to
compensate for that defect:
http://www.cinergy.com/surge/ttip08.htm
That app note shows wrong, right, and preferred earthing because
earthing provided the protector. But then QST Magazine (the ARRL)
says the same thing in July 2002:
The purpose of the ground connection is to take the energy
arriving on the antenna feed line cables and control lines (and
to a lesser extent on the power and telephone lines) and give
it a path back to the earth, our energy sink. The impedance
of the ground connection should be low so the energy prefers
this path and is dispersed harmlessly. To achieve a low
impedance the ground connection needs to be short
(distance), straight, and wide.
...
The goal is to make the ground path leading away from the
SPGP more desirable than any other path.
How curious. That short (low impedance) connection to the single
point earthing electrode (SPGP) is also what both 'top of the front
page' Electrical Engineering Times articles said. However this
remains contrary to many technicians with a history of knowing only
what they were first told.
Even the US Air Force says the effective protector must be connected
short to earth and where utility wires enter the building. As does
lightningsafety.com. As do multiple standards from the IEEE. As
does Dr Kenneth Schneider in:
http://www.arcelect.com/lightnin.htm
As previously mentioned, the connection to earth ground can not
be over emphasized.
...
Conceptually, lightning protection devices are switches to ground.
Once a threatening surge is detected, a lightning protection
device grounds the incoming signal connection point of the
equipment being protected. Thus, redirecting the threatening
surge on a path-of-least resistance (impedance) to ground
where it is absorbed.
Any lightning protection device must be composed of two
"subsystems," a switch which is essentially some type of
switching circuitry and a good ground connection-to allow
dissipation of the surge energy. The switch, of course,
dominates the design and the cost. Yet, the need for a good
ground connection can not be emphasized enough. Computer
equipment has been damaged by lightning, not because of the
absence of a protection device, but because inadequate
attention was paid to grounding the device properly.
Decide based upon the science or because you like someone. These
are mutually exclusive conclusions. The person you like has
repeatedly posted in technical error - in direct contradiction to the
science from even 100 years ago.
Yes, an earth ground rod is not optimal protection. But the single
point earth ground rod is massive protection. Then we spend massively
more money to only achieve a little more protection in telephone
Central Offices. If earth is conductive, one earth ground rod is
sufficient. But if in FL sand and if no surge damage is ever
acceptable, then we spend massively more for that little better
protection:
http://scott-inc.com/html/ufer.htm
http://members.aol.com/gfretwell/ufer.jpg
Demonstrated is Ufer grounds; originally created to that direct
lightning strikes to munitions dump cause no explosion. Just more
examples of how direct lightning strikes must not cause damage. In
every case, that protection is always about a better conductive path
to earth. No earth ground means no effective protection.
The original question is about surge protection for a POTS modem. A
common mode choke is only supplementary protection. It will be all
but useless if the shunt mode protector connected to earth ground does
not exist. Once that 'whole house' protector is properly earthed,
only then might the common mode choke provide additional protection.
Without a better path to earth before entering a building, that common
mode choke will only provide same protection that already exists
inside a modem - easily overwhelmed by the typically destructive
surge. A professionals always demonstrate, surge protection started
by upgrading earth ground to meet and to exceed post 1990 National
Electrical Code requirements.
FCC Part 68.215d(4) requires earthing meet NEC Article 800. That is
the FCC requiring a short connection to earth ground. Article
800.40.A.4
The primary protector grounding conductor shall be as short
as practicable. ...not to exceed 6.0 meters (20 ft) in length.
As every engineering citation notes, every foot shorter than 20 feet
(and no sharp bends, separated from other wires, etc) means even
better protection. The protector is only as effective as its earth
ground - what provides protection.