NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/dcom/telecom/12104

Internet Message Format | 1992-11-21 | 6.2 KB

Path: sparky!uunet!zaphod.mps.ohio-state.edu!news.acns.nwu.edu!telecom-request
Date: 21 Nov 92 19:48:15 EDT
From: [e-mail] (Barton F. Bruce)
Newsgroups: comp.dcom.telecom
Subject: Re: Lightning Protection on Telephone Lines
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In article <[e-mail]>, [e-mail] (Richard
Thomsen) writes:

> I live in the mountains, where lightning and my location are
> synonymous.  I have lost telephone equipment several times.  Once,

Add your OWN premium telco CO grade protection at the service
entrance.  Add arrestors to your power service entrance. Bond both
grounds (as you have done) together with substantial guage wire
without any sharp bends.

That done you have a erected a first wall of defense, and by bonding
the grounds have tried to limit the potential difference seen between
ANY wires from ANY service within your equipment.

Put some MORE protection, ideally on both power and phone line, at
your equipment to clip anything that gets through the front line. This
latter protection may well not be located where you can get a
substantial ground (the 'green' ground wire in branch circuits is a
joke in this situation). At least be sure both phone and power
protection grounds are again connected together in this last ditch
protection. Again you are trying to limit the voltage between any of
the different wires entering your equipment.

Some protection products contain both power and phone protection in a
common package sharing a ground. This is goodness in theory, but most
companies do one type of protection much better that the other. Most
of the el-cheapo protected power strips are a joke, and the ones with
fax or phone jacks, too, are hardly much better.

Bare minimum for the outside phone block is a three electrode gas tube
unit - NOT two of the two electrode gas tube assemblies. The three
electrode design clamps BOTH sides of the line to ground on any arcing
between any two of the three electrodes. Cook and TTI (or is it TII)
make such devices. A common shape is a black log with three wires or
lugs protruding. These come loose to add on top of some earlier design
protector, or in a plastic or metal outdoor housing designed for one,
two, or six, or even twelve units.  Graybar, Anixter, AlTel, North
Supply all carry these, but may not sell to you as an individual. Call
from work.

Inside, you can use even better hardware. CO grade protectors, also
used in higher pair count situations such as office building
entrances, use plug in modules. The are available in MANY grades. The
cheap ones use carbon gaps. Better ones use two electrode gas tubes.
Even better are the three electrode models. Beyond that there are
premium units that take a three electrode gas tube and add fast diodes
and sneak current fuses or heat coils. There are also some
'electronic' units that are very fast but that probably can't hack the
blast a good gas tube can. If you get Porta System's "DELTA" series
modules (three electrode gas + diodes + sneak current) you will be
going VERY well. The diodes are very fast and protect til the gas tube
fires. Diodes alone would get fried too easily.

The DELTA modules we use are # 95BCDXN 230, and are rated for COs with
electronic switching systems. This is the proprietary Porta Systems
shape, but they also make an industry standard slightly less compact
version that plugs into NTI (Cook), ATT, and Reliable blocks. All
those vendors make some similar product. The normal blocks are 25, 50,
or 100 pair! but there are some 6 and 10 pair units that can mount
like a 66 M block.  Something like this in the cellar just inside the
entrance and VERY solidly grounded will nip off whatever the telco
protector misses.  Same supply houses as above.

For home use, the power service entrance protector need not be the
very expensive units you may have seen. GE makes a little grey fist
sized blob that mounts in a standard 1/2" KO on your panel. Other
companies like Delta, whose products are often found at deep well
submersible supply or local electrical supply houses for well under
$40 are very good, and you are not paying $10 or $20 more for the GE
name. These may be silicon carbide units.

At your equipment, there are folks like TripLite with their IsoBar
filters that do a good job on the power, but won't be in the league
with Porta System's CO grade phone protection with their integral
phone line protection in their IsoTel combined unit. OTOH Porta
Systems makes a "Six Pack +" that is a six-pair block to take the
plugin protectors (get the Delta series not their lesser units) and
that has a power protector built in. The power part may snub well but
lacks the additional filtering of the TripLite units. The Six Pack +
has open 66 type punch clips and is designed for WALL mounting, not
for dangling behind your desk. It really targets small keysystems -
power and phone lines together, and additional phone only blocks can
be grounded to it for larger systems needing more than six-pair.

The real bottom line is that there is NO ONE GOOD UNIVERSAL product.
And protection at just one place in the fairly FAT guage power line is
NOT enough. The Delta class phone protection may be enough at just one
location, but more is better.

Catching and dumping to ground as much as possible at the entrance is
very desirable. Spit and polish cleanup of anything left on the lines
can then more safely be handled by typically poorly grounded
protection AT the equipment needing protection. This latter protection
at least clamps ALL wires entering your box to be within modest
voltage of each other -- reguardless of how many volts are between
there and outside ground, or of which service's wires are guilty of
carrying in the danger.

If you have a direct hit, all bets are off. But anything further out,
even a few poles away, and you have a good chance of being able to
handle it.

You spoke of driven rod grounds. No city water lines? Any well
casings?  Good wet earth? or rocky dry sandy soil? Sometimes an array
of driven rods spaced some feet apart can help.