telephone wire/lightning strikes
r1100...@yahoo.com
to our house which is about 500 yards distances in a 2 ft deep trench.
I will also be laying a water line to use in case of bush fires.
Would the phone line be prone to lightning strikes, Have been told
that laying a s/steel wire along the line in the trench would solve
the problem. Any ideas would be appreciated.
cheers Ed
Western Australia
Don Bruder
r1100...@yahoo.com wrote:
If it's buried, lightning won't bother it, whether or not you take any
kind of special precautions. The buried portion will be plenty safe from
strikes, because lightning is looking for the easiest path to ground,
which in this case is the earth itself. By definition, the fact that the
strike has happened means that the circuit (cloud to earth) has been
completed, and the charge has pretty much reached "the end of the line".
Now that doesn't do anything to prevent damage from the strike that hits
an aerial part of the phone line... But at least in theory, the aerial
lines are already lightning-protected by various methods (none of which
are certain to make any strike harmless to equipment attached to the
wire, unfortunately, but they do at least *TRY*) that are generally
plenty adequate. Not to mention probably being outside your budget,
unless you're the guy who signs the checks for a good-sized
corporation... :)
--
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Hate SPAM? See <http://www.spamassassin.org> for some seriously great info.
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Louis Boyd
> In article <faf900b7.03092...@posting.google.com>,
> r1100...@yahoo.com wrote:
>
>
>>i laying a phone line from the corner of our property up a steep slop
>>to our house which is about 500 yards distances in a 2 ft deep trench.
>> I will also be laying a water line to use in case of bush fires.
>>Would the phone line be prone to lightning strikes, Have been told
>>that laying a s/steel wire along the line in the trench would solve
>>the problem. Any ideas would be appreciated.
>>cheers Ed
>>Western Australia
>
>
> If it's buried, lightning won't bother it, whether or not you take any
> kind of special precautions. The buried portion will be plenty safe from
> strikes, because lightning is looking for the easiest path to ground,
> which in this case is the earth itself. By definition, the fact that the
> strike has happened means that the circuit (cloud to earth) has been
> completed, and the charge has pretty much reached "the end of the line".
I hate bear bad tidings, but dirt, sand, soil, even water have much
higher resistance than copper wire. The point where lightning hits
"ground" is certainly NOT the end of the circuit. Very significant
currnts and voltages can appear in the physial earth for tens or
hundreds of feet from the point of a lighting strike. Burying cable
does not automatically provide protection from lightning strikes. It is
only a little less probable that lightning will strike a buried cable
than one located on poles. Putting in a paralleling steel wire won't
help much. Putting the cable in a plastic conduit won't help much in
preventing the cable from being damaged if lighting does strike close.
Putting it in a steel conduit will protect the cable from being
burned, but it provides little protection for equipment tied to the cable.
Any time you run a cable from the outside of a house to the inside (if
it goes any significant distance outside) , it makes sense to put
lightning protectors on each conductor. Kind of protectors varies with
what kind of signal the conductor is carrying. For power, metal oxide
varistors plus circuit breakers work well. For telephone circuits
generally a three terminal gas tube is used. These are small metal and
cermaic spark gaps containing a low pressure gas. There are two end
plates which go to the paired wire of each phone circuit, and a center
ground ring which is tied to the house ground. (this ground should be
shared by both power and telephone, and also go to a physical ground rod
or buried water pipe). If the voltage exceeds about 250 volts the gas
inside the tube ionizes and shorts BOTH condutors to ground at once.
The gas tubes are small, about 1/4" diamter and a half inch long, but
they can carry very heavy current for a few milliseconds. Such tubes
are found in the telephone entrance box on everyone's home. There is
some variety in what they look like. When the heavy current ceases the
gas quits conducting and returns to normal. For RF circuts, like
antenna leadins different circuitry is used.
> Now that doesn't do anything to prevent damage from the strike that hits
> an aerial part of the phone line... But at least in theory, the aerial
> lines are already lightning-protected by various methods (none of which
> are certain to make any strike harmless to equipment attached to the
> wire, unfortunately, but they do at least *TRY*) that are generally
> plenty adequate. Not to mention probably being outside your budget,
> unless you're the guy who signs the checks for a good-sized
> corporation... :)
Direct strikes to phone lines almost always do some physical damage to
the cable. Aerial phone lines are usually located under power lines and
the top most wire on most power lines is a grounded "sky wire" designed
to take lightning hits so the direct lighting bolt rarely hits an aerial
cable. Buried cable is statisticaly less likely to have a close hit,
but it's not as well protected if a hit does occur.
Buried phone cables generally have a metallic outer sheath coverd with
thin polyethylene which is grounded ever few hundred feet. On moderately
large cables (25 pair or more) this sheath is capable of carrying the
current of lightning strikes to the nearest ground or it may simply
puncture the poly and continue to dissipate into the earth. It can do
that repeatedly before the interal pairs are damaged. Small cables for
the local home drops simply aren't heavy enough to withstand direct hits
even if they have a shield. There is an advantage to putting the phone
line in plastic conduit. Getting a direct hit by lightning is rare but
if it does happen the conduit will make replacing the wire a lot easier.
It also make it less likely the wire will get cut if someone is
digging as the conduit is a lot more obvious than a small phone cable.
--
Lou Boyd
Gary Coffman
The main concern is common mode induction due to the earth
currents generated by a lightning strike. The best defense you
have against that is to make sure one end of the line is floating
with respect to earth. In other words, use a grounded surge
suppressor only at one end of the line.
Gary
Louis Boyd
I have to argue with that advice.
A telephone circuit is pretty useless if it doesn't have electronic
equipment on both ends. Lightning phenomina are generally high voltage
transients but of short duration. Telephone cables can stand high
currents for brief durations but if they arc between wires or to ground
there are usually carbon tracks generated resulting in permanent noise
conditions requiring replacement of the cable. For these reasons ALL
telephone circuits, at least all used in the US, have "surge
suppressors" in the form of gas tubes at both ends of each pair of
wires. The may have more, they will have these protectors (as they are
called in the industry) at each building entrance as the first piece of
equipment on the line before any other electronic equpment is
encountered. They may also appear in remoted repeater cabinets placed
in the field. These are mostly three terminal gas tubes though there
are some which used semiconductor devices. Besides protecting the
equpment on each end of the cable and the cable, the use of suppressors
on each end protects humans working on equipment at each end (and to
some extent those working on the cable in in the field) from high voltages.
There are cases where severe induction from paralleling power lines
induces enough current into a telephone cable to heat the conductors to
the point of melting the insulation or even fusing the wires. Had the
protection devices not been in place at one end the cable might have
survived without damage. However, there would have been potentially
lethal voltages induced on the open end of the cable. Sorry, but your
advice of putting surge protectors at one end of a telephone circuit
only is ill advised and dangerous.
--
Lou Boyd
MSH
"Don Bruder" <dak...@sonic.net> wrote in message
news:qqPdb.25453$dk4.7...@typhoon.sonic.net...
> If it's buried, lightning won't bother it, whether or not you take any
> kind of special precautions
Hah, hell it won't. Our phone lines are buried for miles and me and several
neighbors have had various computer components fried through the phone line.
Modems, motherboards....
MH
Halcitron
>Newsgroups: misc.rural
>Date: 28 Sep 2003 20:23:49 -0700
Ed, get one of those Surge Protectors, that plugs into the wall outlet, and has
a few telephone jacks to protect phone and modem. Cost under a US$100
caveat lector
Halcitron misc.survivalism
Check your six and know when to duck.
NRA Member since 2002
The Law of the Land, is the weapon in your hand.
Smith & Wesson starts where the Bill of Rights stop.
w_tom
modem was damaged. Therefore it must have been on phone
line. Wrong. 4th grade science says electricity first must
form a complete electrical path. Only after the formation of
a complete circuit, only then does something fail. Damaged
item must have both an incoming and outgoing electrical path;
else no damage.
Phone lines typically have a 'whole house' protector
installed free by the telco. Therefore phone lines typically
are not the source of the incoming path. Most common path for
surges that damage modems and portable phone base stations -
AC electric. Incoming is on AC electric. Outgoing must be
some path to earth ground. Outgoing path would be phone
line. As a result, damage to modem's DAA section is a common
symptom of a surge incoming on AC electric.
Accurately stated: it is does not matter whether wire is
buried or overhead. They are all sources of destructive
surges as demonstrated in this figure on how effective
protection is installed for two structures. Note each
structure has a central earth ground AND all incoming
utilities - even buried one - must first be earthed before
entering the structure:
http://www.erico.com/erico_public/pdf/fep/TechNotes/Tncr002.pdf
As the figure demonstrates - even buried wires can be a
source of destructive surge. Reasons for modem and
motherboard damage is often due to AC electric - a surge that
seeks earth ground via the phone line - which is why modems
can suffer the 'No Dialtone Detected' error message.
Louis Boyd
He's correct that the phone company provides a whole house protector at
the telephone entrance. The power company does not provide a protector
at the power entrance but it's easy to add one. Any decent electrical
supply house sells MOV surge protectors. These are a three wire device
which mounts on the breaker panel, usually in a 3/4" knockout. They
wire just like any 240 volt load to a dual 20 or 30 amp breaker, with
the third wire going to the neutral. The voltage on the two hot leads
should not exceed 200 volts peak in normal operation, so these devices
clamp any spike over about 300 volts to ground (the ground and neutral
are common at the entrance breaker). They're typically rated 10,000
joules (watt-seconds) which will handle most pulses on power lines
caused by lightning and cost about $100. They are typically a metal boxe
about 3" x 2" x 5" and have two LED's to show the MOV is working
properly. They're designed so if the MOV blows out (possible but rare)
or the unit gets disconnected the lights go out. They draw negligable
power so the only cost is the initial purchase. I have them on all
five building entrances on my property and they definitely work. Three
of the buildings are an automated observatory on a 5500' mountain peak.
Lightning hits are common and damage to the many computers there is rare.
The other requirement for this to work is that the telephone ground and
the power entrance ground must be common. Just tie them directly
together with #6 copper in as direct of path as practical.
--
Lou Boyd
(Electrial engineer and 22 years telco transmission engineer,
now director of Fairborn Observatory)
http://www.fairobs.org
MSH
and I are all on separate solar systems. We have no power company wires
here. The neighbors whom I know were affected live miles apart. My power
system has about 20 feet of buried wire. The lightening that took out our
computers on several occasions did not strike anywhere near that 20 feet,
nor have I heard of any other strikes near houses and systems. The
lightening arrestors on our power systems were unaffected. Phone and house
grounds are separate. How'd that work?
MH
"Louis Boyd" <bo...@apt0.sao.arizona.edu> wrote in message
news:blcb1u$r1a$1...@oasis.ccit.arizona.edu...
Louis Boyd
> That all sounds good, but lets throw this into the equation. My neighbors
> and I are all on separate solar systems. We have no power company wires
> here. The neighbors whom I know were affected live miles apart. My power
> system has about 20 feet of buried wire. The lightening that took out our
> computers on several occasions did not strike anywhere near that 20 feet,
> nor have I heard of any other strikes near houses and systems. The
> lightening arrestors on our power systems were unaffected. Phone and house
> grounds are separate. How'd that work?
Right there is your problem. If your phone and house grounds are
separate then if a voltage is applied to either it will flow through you
delicate equipment to the other. You must bond the phone and power
grounds together.
--
Lou Boyd
w_tom
Lightning that took five miles to obtain earth ground through
a church steeple instead took a path only a few feet off to
one side. Down a metal wire to earth instead of using the
church.
That is the concept of surge protection. Plug-in protectors
would have you believe they are stopping or absorbing a
surge. They deceive. Surge protectors are effective when the
surge is provided a shorter, more (electrically) direct path
to earth. Therein lies the advantage and secret of 'whole
house' protectors. They connect lightning to earth before
lightning can find an earth ground path inside the building.
Surge protection works only when it shunts (diverts) a surge
to earth ground. Shunting to earth is most easily
accomplished right where utility wire attempts to enter
building.
Some minimally sized 'whole house' protectors for
residential AC are sold in Home Depot as Intermatic EG240RC or
IG1240RC, or Siemens QSA2020. A few other AC electric 'whole
house' protectors:
http://members.home.net/kapland/surge.htm
http://www.dale-electric.com/ditek.htm
http://www.deltala.com/prod01.htm
http://www.deltala.com/prod02.htm
http://www.ditekcorp.com/dispInfo.cfm?ID=280
http://www.ditekcorp.com/dispinfo.cfm?id=579
http://www.ditekcorp.com/dispfamily.cfm?id=3
http://www.ch.cutler-hammer.com/surge/products/chsp.html
http://www.squared.com/us/squared/corporate_info.nsf/unid/ECA90110AB7098
or http://makeashorterlink.com/?Z1B7539A1
http://www.leaintl.com/pdf/HSPCCutsheet.pdf
http://www.leaintl.com/pdf/PBSCutsheet.pdf
http://www.leaintl.com/pdf/MsaCutsheet.pdf
http://members.tripod.com/~StorminProtection/index-31.html
http://www.nooutage.com/LightningSurgeProt.htm (LA-302)
http://www.keison.co.uk/furse/furse06.htm
http://www.mimcv.com/residential.html
and one from Leviton but their web site does not make URLs
easy.
Bob Adkins wrote:
> I'm sure you have seen lightning arc 5 miles from cloud to ground.
> If it can do that, what's another inch or 2?
>
> Bob
w_tom
that was struck by lightning. Those sleeping parallel to the
tree were unaffected. But two who were sleeping perpendicular
to the tree suffered severe electrical shock. Surge went down
the tree, into boy's feet, through boy's body, out through
boy's head, and ongoing through earth. Note the prerequisite
incoming and outgoing electrical path. This example also
demonstrates why multiple grounds could be responsible for
computer and modem damage. Required is single point earthing
- even to avoid electrical shock on the gold course. Keep
your feet together.
You know that to be damaged, a current must first flow
through the appliance. There must be both an incoming and
outgoing path. And that outgoing path must connect to earth
ground.
Figure 2 demonstrates the concept. Notice that a halo
ground also creates a central earth ground:
http://www.cinergy.com/surge/ttip08.htm
Polyphaser, a benchmark in protection, demonstrates same in
this application note:
http://www.polyphaser.com/datasheets/PTD1028.pdf
> Lightning strikes somewhere across the street close to the below
> grade West cable vault. ... The first line of defense is the
> telco protection panel, but the panel must be connected to a low
> resistance / inductance ground. There was no adequate ground
> available in the telephone room.
Doug Younker
conducted in the state of Florida by power companies. As I remember it
burial does not mean protected by lightning strikes and the lightning
did travel through the earth to find cable to damage. Does that mean
that your phone line will be prone to strikes? Probably not, but I'm
clueless as how to predict the danger. Your best source of information
has to be your telephone service provider. Any way if the water line
you are laying in the ditch is plastic it couldn't hurt to lay wire in
the ditch to facilitate relocating if needed later. The telco wire
should and may suffice, 500 yards of wire may be too expensive of
insurance.
Doug
w_tom
example, many assume high mountains are most often struck.
Not necessarily. Experience indicates that the valley may be
struck more often - a function of geology and ground water.
More often side of mountain rather than top of mountain is
struck - in direct contradiction to widely held beliefs.
More on this is found in two long discussions in this
newsgroup entitled:
Storm and Lightning damage in the country 28 Jul 2002
Lightning Nightmares!! 10 Aug 2002
http://tinyurl.com/ghgv or http://tinyurl.com/ghgm
No reason to be clueless about surge protection.
Installation to make surge damage redundant is quite simple.
Concepts that explain that installation are summarized in
those above discussions.
Surge damage from buried wire need not involve the direct
strike as in that PBS show (and fulgerites). Incoming
transient on buried wire was explained by citations and
examples in my previous post.
Doug Younker wrote:
> I recall a program that ran on PBS about an lightning experiment
> conducted in the state of Florida by power companies. As I
> remember it burial does not mean protected by lightning strikes
> and the lightning did travel through the earth to find cable to
> damage. Does that mean that your phone line will be prone to
> strikes? Probably not, but I'm clueless as how to predict the
> danger. Your best source of information has to be your telephone
> service provider. ...
Gary Coffman
>Gary Coffman wrote:
>> On 28 Sep 2003 20:23:49 -0700, r1100...@yahoo.com wrote:
>
>> The main concern is common mode induction due to the earth
>> currents generated by a lightning strike. The best defense you
>> have against that is to make sure one end of the line is floating
>> with respect to earth. In other words, use a grounded surge
>> suppressor only at one end of the line.
>>
>
>I have to argue with that advice.
>
>A telephone circuit is pretty useless if it doesn't have electronic
>equipment on both ends.
Well, I'll have to argue with that. I've found models 300 and 500
Western Electric phones to be very useful over the years. Model
300s don't have any active electronic devices. Model 500s may
have a touchtone pad containing a couple of transistors, but since
that is powered by the phone line, common mode currents don't
bother it.
In fact, common mode currents aren't a problem unless you provide
a complete circuit for them. By floating one end of the phone line,
and providing a suppressor to Earth at only one end, you eliminate
a path for common mode currents. You also avoid closing the loop
for induction due to Earth currents caused by the strike.
>Lightning phenomina are generally high voltage
>transients but of short duration.
Lightning is best modeled as a 20 kiloamp constant current source.
The maximum available voltage cloud to ground is millions of volts.
But the voltage along any particular part of the cloud to ground path
is I*R. Along copper lines, very low R, it will generally be quite moderate.
But as I noted, the current will be very large (for a very short time, on
the order of 20 microseconds).
Single point (equipotential) grounding is central to any effective lightning
mitigation system. I design and install lightning mitigation systems for
broadcast plants. I've got 35 years experience in this field. The one fact
you can count on is if there is no potential difference between two points,
no destructive currents will flow through the equipment bridging those
points. I can tell you with great confidence that separately grounding
both ends of a long twisted pair is a recipe for destroyed equipment.
Gary
w_tom
> ... In addition, where there exists a lightning exposure,
> each interbuilding circuit on a premise shall be protected
> by a listed primary protector at each end of the
> interbuilding circuit.
If I remember the numbers correctly, a phone will typically
have 1500 volt isolation or breakdown voltage. Any transient
that exceeds that breakdown voltage finds earth ground,
destructively, through the human user. That is but one reason
why a wire between each building must be earthed, as required
above, at both buildings.
In another example, let's say that wire is only earthed at
the distant end. In this discussion, a buried wire (in west
cable vault) connects to building at its unearthed end.
Damage results because the unearth end of wire entered that
building:
http://www.polyphaser.com/datasheets/PTD1028.pdf
> Lightning strikes somewhere across the street close to the below
> grade West cable vault. ... The first line of defense is the
> telco protection panel, but the panel must be connected to a low
> resistance / inductance ground. There was no adequate ground
> available in the telephone room.
charles krin
>In article <faf900b7.03092...@posting.google.com>,
> r1100...@yahoo.com wrote:
>
>> i laying a phone line from the corner of our property up a steep slop
>> to our house which is about 500 yards distances in a 2 ft deep trench.
>> I will also be laying a water line to use in case of bush fires.
>> Would the phone line be prone to lightning strikes, Have been told
>> that laying a s/steel wire along the line in the trench would solve
>> the problem. Any ideas would be appreciated.
>> cheers Ed
>> Western Australia
>
>If it's buried, lightning won't bother it, whether or not you take any
>kind of special precautions. The buried portion will be plenty safe from
>strikes, because lightning is looking for the easiest path to ground,
>which in this case is the earth itself. By definition, the fact that the
>strike has happened means that the circuit (cloud to earth) has been
>completed, and the charge has pretty much reached "the end of the line".
Might want to look up 'fulgerites'...and see what the U Florida (I
believe it's the Gainsville U...as the area that they are conducting
their tests is at the National Guard base just down the road) folks
are doing to predict what happens when the lightning strikes the
ground...
>
>Now that doesn't do anything to prevent damage from the strike that hits
>an aerial part of the phone line... But at least in theory, the aerial
>lines are already lightning-protected by various methods (none of which
>are certain to make any strike harmless to equipment attached to the
>wire, unfortunately, but they do at least *TRY*) that are generally
>plenty adequate. Not to mention probably being outside your budget,
>unless you're the guy who signs the checks for a good-sized
>corporation... :)
I believe that there are now gas discharge set ups to ground most any
incoming severe surge...
Try "Polyphaser" in your search engine of choice...
ck
--
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building, But here was a good reason for the move.
You can't post "Thou Shalt Not Steal" in a building full of lawyers and
politicians without creating a hostile work environment.
Edna H. on alt.books.m-lackey, 20030930