Those effective 'whole house' protectors
make a connection from each phone wire to earth ground.
Surge on a NA phone line is earthed before it can enter the
building.
One comment here...this also depends on the 'IN' house wiring being done correctly or is undamaged.....in older homes where the
lines have been butchered this does not hold true...
especially on the NID on the side of the house, seen them knocked off with lawnmowers etc,,....just hanging there by the wires,
ground ripped off.
"w_tom" wrote in message ...
First, Richard is in Australia where he has little (probably
no) experience with effective protection. For example,
telephone companies in North America install 'whole house'
protectors at each customer's premise interface with a
connection to earth. Those effective 'whole house' protectors
make a connection from each phone wire to earth ground.
Surge on a NA phone line is earthed before it can enter the
building.
Richard would not know about this because Australian telcos
typically do not provide effective surge protectors - for
free. IOW in Australia, surges incoming on phone line are
possible - just one more path that makes surge damage even
that more likely. Just another reason why Richard would
speculate that surge protection is not possible. How would he
know? He does not have any. If he has no protectors, then
how would Richard know that properly sized and earthed surge
protectors are effective?
Second, phone lines at the exchange are earthed. Earthing
(via surge protectors) is located to be distant from the
switching computer - up to 50 meters separation. That
separation between surge protector and transistor is part of
the surge protection 'system'. Every wire entering that
switching center must first have a connection to central earth
ground - either by direct connection or via surge protector.
Why does Richard also not know this? Why is he so critical
and yet does not even know basic wiring and earthing inside a
telco switching center?
Earthing is so effective that, for example, emergency
response operators don't remove headsets during
thunderstorms. No surge entering on phone lines. This is old
technology proven long before WWII. Richard is speculating
without even having learned what has been proven generations
ago - before WWII. Effective surge protection is about
earthing the surge. So effective that surge damage is
considered a human failure.
Third, if Richard knew basics of surge protection, then he
would know that DC resistance is irrelevant. Wire impedance -
not resistance - is the important number. If he knew his
'stuff', then he would identify the component that keeps an AC
mains surge from finding earth ground via a modem. It only
takes a multimeter. A direct connection exists between some
pins on modem ICs and one AC electric wire. A direct
connection that makes modem damage from AC electric possible.
So where is this 'isolator' that keeps an AC mains surge from
finding modem? Richard tells us that AC mains cannot connect
a surge through modem. Then Richard can tell us which
component isolates modem from AC mains surges?
Richard also does not know the energy content of a lightning
strike. He only speculates. Alan Taylor of the US Forestry
Service demonstrated the energy content. In more than 95% of
lightning strikes to trees, the strike left no perceptible
indication that a strike had even occurred. That's right.
Lightning strikes typically are not high energy events. Many
are such low energy events as to not even leave indication.
Lightning is a high power event; not high energy event.
Richard should enlighten us with numbers of his high energy
lightning strike. Therein lies another problem with his
speculations. He provides no numbers to go along with his no
experience.
In the meantime, even the US Army demonstrates in training
manuals what is required to earth a direct lightning strike.
They require 10 AWG (2.5 mm dia) wires to connect lightning
rod to earth. That thin wire connects the direct lightning
strike from air terminal to earth without damage - because
energy content in lightning is that small. Just more numbers.
Lightning is easily earthed without damage. The art of
surge protection is earthing - to keep the surge outside of
the building.
One path for destructive surge that is permitted inside a
building: incoming on AC electric, destructively through mode,
and outgoing to earth ground on phone line. Damage because
one incoming wire - AC electric - was not earthed (via 'whole
house' surge protector) before entering building.
Effective surge protection is about earthing every incoming
wire before it can enter the building. Once inside a
building, the surge will find numerous, destructive paths to
earth ground. Surge protectors are only as effective as their
earth ground.
Richard Freeman is invited to describe the component that
keeps an AC mains surge from finding path through modem.
Richard is invited to put up some energy numbers for a CG
lightning strike. Richard is invited to contradict US Army
Training Manual 5-690; to prove that earth direct lightning
strikes cannot be earthed using only 10 AWG (25 amp) wires.
Richard is invited to put some scientific numbers up with his
speculations. If he cannot provide the numbers, then he is
only promoting junk science reasoning.
In the meantime, a common destructive path for modems is
incoming on AC electric and outgoing to earth ground via phone
line. A path proven too often by tracing the surge and
replacing damaged components in that path. It called
experience that is in agreement with underlying theory,
research papers, and industry professionals.
Richard Freeman wrote:
--------snipped for brevity------------
Firstly where is this earth on the Telephone line ????? - It does not
exist.
In normal circumstances the phone line ground is at the exchange.
However, in the case of a lightning strike, the nearest earth is the
ground surrounding the cable. In any case, if lightning were to hit
the ground, then why would it not dissipate itself in the general mass
of earth rather than travelling all the way into the house and onto
its local mains earth? Granted, the earth is not homogenous, so a
lower potential _could_ exist at the dwelling, but it would seem more
likely that an earth strike would not propagate too far away from the
epicentre.
Firstly A single earth point is usually a relatively poor earth often
providing up to tens of Ohms Resistance to 'earth' when Lightning hits say
an earth stake that earth point typically rises to 50,000V or more above
nominal Earth as a result.
There have been many cases where a Lightning strike to the ground has blown
through the insulation of a cable and travelled through it to a better
ground however this usually also causes physical damage to the phone cable.
Secondly the Phone line is not earthed back at the exchange it is in fact
floating above ground potential - It needs to be as it is a Balanced
Circuit.
Thirdly the DC resistance alone of a phone line is fairly high typically
being in the order of a hundred or more Ohms especially when compared to the
mains.
In other words any earth on a typical Phone line is nowhere near as
effective as the earth provided by the MEN AC distribution System.
some (in Australia very few) phone lines have surge arrestors but these
are
not generally implemented as they have proven to be ineffective in the
case
of near/Direct strikes.
going through your list :
Firstly, my friend's neighbour lost his electrical distribution box,
so this confirms that the strike came in on the mains.
Well Maybe and I have not said it never comes in via Mains just that if
it
does it is so uncommon that I have not seen it.
I have seen it twice at the same dwelling, with similar results. On
the second occasion the datapump of an internal 33.6K ISA Rockwell
modem was damaged, but the only other problem with the entire PC was a
faulty IRQ3 signal on the ISA bus. That's two PCs, neither of which
sustained any damage other than a faulty modem DSP/DAA.
So the damage was to the modem both times! this was likely to have come via
AC mains because ?
Reading through the list of damage however suggests that your friend
suffered a direct strike in which case :
A) all bets are off
B) a Lightning strike that has blown the ****e out of a switchboard is
barely going to flinch at blowing the ****e out of a MOV
C) Equally likely and the more probable scenario is that your friends
house
was hit and the Lightning followed the path to the best Earth available -
that of the MEN Mains
Failure of PCtel DAA module (plug-in type for PCChips M585LMR
motherboard). Symptom was "NO DIALTONE". Parallel telephone was
undamaged. Both phone cables were plugged into a "protected" power
board.
Plug in module connected to the phone line - still matches the scenario
that
the strike came in via Phone and exited via Mains
The parallel phone most likely rode out the strike. In fact this sounds
like
a module in a PC if the strike came in via the Mains and exited via the
phone line why wasnt the PSU fried ?
Clearly the strike struck the mains at some point, so one would
intuitively expect that everything connected to the mains would have
suffered significant damage, as you say. The fact that the PSU
survived suggests that the major part of the potential difference
appeared across the DAA of the modem (???).
most likely it came in via the floating phone line and headed for the MEN
earth - it was possibley even sufficent to cause localised EPR (Earth
Potential Rise) however given the relatively low impedance House wiring
(against the Higher impedance phone line for eg ) and the relatively high
impedance path from the phone line to the Mains earth most of the voltage
for the strike would have appeared between the phone line and the mains
earth.
the more likely scenario is that the
strike came in via the phone line and headed for the chassis earth on the
PC.
So we have two strikes, one on the mains and another on the phone
line?
Nope one strike most likely direct to the house/Aerial/Phone line and a
****e load of current heading for the MEN earth inducing all sorts of
voltages in and around the house wiring.
(2) Portable telephone base station - shorted 15V zener diode at tip
and ring inputs.
Powered phone connected to the phone line - still matches the scenario
that
the strike came in via Phone and exited via Mains
(3) Television - shorted rectifier diode, blown fuse, and failures in
the +5V regulator, remote sensor, and microcontroller.
(4) Two VCRs - CPU and power supply failures.
Nasty sounds like a direct strike which also entered via the TV aerial
and
headed for the earth provided via the double insulated mains - note no
phone
line involved here
So now we have three strikes, one on the mains, a second on the phone
line, and a third on the aerial?
Nope still only one direct Strike and a bunch of induced current in various
bits of metal a single Lightning strike can and often does induce fairly
high currents/voltages through nearby wiring especially in a Direct (or even
near) Strike. One main strike though.
bear in mind that w_tom s 'whole house protection' would most likely not
have saved anything in this strike either.
BTW, no tuners or IF stages were damaged.
(5) Audio unit - CPU failure, P/S OK.
Dont know what this was but if double insulated equipment connected to
the
VCR/TV then Lightning was probably still travelling in via the TV aerial
and
had not dissipated completely via the VCR or TV Again no phone line
connected here
No aerial, no phone line, just mains power.
still have no idea what this is - speaker cables or signal cables ?
(6) Security light - faulty power controller, light dims but won't
turn off.
Sounds like a direct strike The Light being installed outdoors probably
copped a secondary strike not the full Strike - you would have found
that
one of w_toms surge busters would not have saved this anyway. Also no
phone
line involved here
(7) TV - blown fuse, damage to P/S
entered via the TV aerial headed for the AC mains again no phone line
involved here
As before, no tuners or IF stages were damaged.
Double insulated telly though most likely so that the highest impedance part
of the path to earth (and hence the higher voltage across components) would
have been through the PSU. The TV most likely even had some surge supression
for thhe Aerial which would have excacerbated this failure.
Well sounds like your Lightning still mostly obeyed the laws of Physics
and
entered by unearthed / poorly earthed paths and headed straight for the
best
earth available that of the AC Mains. as an addendum the mains in this
instance probably rode out the strike to a certain degree but in all the
cases a path for the lightning to have entered by other than AC mains
exsists.
Lightning aint Rocket science it obeys the laws of physics - it is just
with
high energy events such as lightning different laws of physics often come
in
to play.
Lightning seeks a path to the best earth it can find and note here that a
single earth stake buried in the ground is more often than not hardly the
best earth available the MEN system however used for 240/415V mains
distribution however frequently offers a superior earth for Lightning
strikes
I notice that the one thing that distinguishes a PC from most, if not
all the other equipment is the fact that it has an earth conductor.
What if this relatively small earth conductor allows the PC to float
to the strike potential? Wouldn't the full potential then appear
across the modem's DAA rather than the main part of the PC?
The earth conducter to a PC is going to still going to have a resistance of
a fraction of an ohm against over 1000's of ohms to earth via the Phone line
Regards
Richard Freeman
I wonder if there is some forensic or metallurgical method of
determining the direction of current flow in a lightning strike.
why ?
just think about it compare the two earths -
MEN AC Mains earth = fraction of an Ohm to Earth - Directly connected to
earth stakes at not one but Several Places with a minimum wire size of 2.5mm
square (O.k with typically 2 m of 1.5mm square cable for the IEC power
lead).
Phone Line = floating above Earth potential with a Maximum wire size of
0.28mm Square not connected to an earth anywhere.
Which sounds like the better earth to you ?
If you where Lightning where would you head ?
It is not rocket science it is just fairly basic electrical theory - very
simple physics. Dont be mislead by the wilfully ignorant especially those
who seem to have a vested interest in selling 'whole house protection'.
Regards
Richard Freeman
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