Dial up modem problem

Richard Freeman wrote:
Wrong the reason I know Telco Surge protection is no defense
against near or direct strikes is that I have seen Time and Time
again surge protection literally blown off the distribution frame
(where it has been installed) and equipment on those lines dead
following near or direct strikes.

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?

how big then I have certainly seen 1 Joule MOVs destroyed - yes
with short Earth leads to the mains/Switchboard earth stake


So where does Richard find this 1 joule MOV? Even tiny MOVs
costing less than $0.05 are 30 joules. Radio Shack sells a
small MOV that is 70 joules. And yet neither would be
sufficient for 'whole house' protection. Richard says he saw
a 1 joule MOV destroyed because he invents this number. Where
does he find a 1 joule MOV? He does not even know basic
numbers. Even undersized power strips start on the order of
300 joules!

Richard Freeman posts "1 joule" because he was challenged to
post a number. So he had to invent that number. He argues
incessantly without technical knowledge. He demonstrates no
knowledge of electricity beyond installing PA systems. Using
junk science reasoning, he must avoid or invent his numbers -
such as a mythical 1 joule MOV.

If Richard had technical knowledge, then he knew even 100
joules was grossly undersized. But his (mythical) surge
protector was damaged by a surge. Of course. 1 joule surge
protector would be grossly undersized - quickly destroyed -
and therefore useless. No wonder he claims surge protectors
don't work. He tries to stop a flood with a sponge!

Did his mythical protector have a short connection to
earth? Of course not. This earthing requirement was
completely new to him. Suddenly that mythical 1 joule MOV is
now provided:
with short Earth leads to the mains/Switchboard earth stake.

Why would he install a 1 joule surge protector with a short
connection to earth when he insists that all surge protectors
are useless? When Richard finally posts a number - the 1
joule protector - it is a number that does not even exist!
Now he invents a short connection to earth ground. But the
deception continues.

To confuse others, Richard posts half facts:
Lightning does vary in strength but is Typically between
1,000,000,000 and 10,000,000,000 Joules

And where is most all that energy dissipated? To deceive,
Richard forget to mention all of what Dr Uman says. In his
book, Dr Uman then continues:
Most of the energy available to the lightning is converted along
the lightning channel to thunder, heat, light, and radio waves,
leaving only a fraction available at the channel base for
immediate use or storage.

Maybe Richard would now like to post how many joules
actually exist at the strike location?

Posted previously was this challenge:
Then Richard can tell us which component isolates modem
from AC mains surges?

He responds:
It is a very simple device in use since before World War 1 called
a Transformer another very simple device which has been in use
for well over 100 years is called a capacitor

Well then all we need do is install transformers and
capacitors on all incoming wires. Then never suffer surge
damage? However Richard tell us that nothing can protect from
direct lighting strikes. He cannot have it both ways. Either
transformers and capacitors mean no surge damage - OR -
transformers and capacitor, like surge protectors, are not
effective protection from the direct strike.

Reality: those devices have a breakdown voltage. They
become short circuits at excessive surge voltages. As posted
earlier, all appliances contain effective surge protection.
What do they use? Galvanic isolation (transformers) and
capacitors. Effective protection IF the surge is earthed
before it can enter the building. Effective internal
protection if the building uses 'whole house' protectors and a
single point earth ground.

In the meantime, that modem has a direct connection to one
AC main wire - in direct contradiction to Richard's post. But
then Richard never did the multimeter testing. That AC main
wire is why modems tend to be easily damaged by AC main
surges. AC main surge that was not earthed using a 'whole
house' protector. Protection using transformers exists in
appliances and in that modem. Protection that is overwhelmed
if surges are not earthed using 'whole house' protection.

But again, these are old and well proven concepts. Concepts
that Franc Zabkar has also demonstrated.


Richard Freeman has become a sounding board so that lurkers
can learn about effective and ineffective surge protectors.
So that lurkers can learn how modems may be damaged from
surges that entered on AC mains - the "No Dialtone Detected"
message. But Richard Freeman serves no more purpose to this
thread. He invents rather than first learns his facts. That
mythical 1 joule MOV being a classic example. The
misrepresentation of what Dr Uman posts being another
example. The transformer and capacitor that would provide
surge protection - protection that 'whole house' surge
protectors and single point earth ground cannot - according to
Richard.

Modem protection means that all incoming utility wires -
especially AC electric - must have an earth ground connection
before entering the building. Modem damaged because AC
electric had no properly installed 'whole house' protector. A
surge protector being only as effective as its earth ground.

Yes. Lawn mowers can cut more than grass and toes. But
then we humans are assigned the job of inspecting and
correcting those earth grounds. There is no other way to
verify a properly earthed home. Only a human can find and
correct a missing earth ground. No reasonably priced test
equipment can locate or correct a missing earth ground. The
most powerful tool for finding a defective earth ground is
the human eye.

Usually the telco installs that NID properly. But
installation assumes the building provided an effective
earthing system when phone was installed. In simple terms,
the house must meet or exceed post 1990 NEC earthing
requirements. That would provide a minimally acceptable
single point ground necessary for 'telco provided' surge
protector (that is inside NID). But many older homes don't
even have earthing that meets older code as JAD notes.

Wiring inside the house is mostly irrelevant to an effective
'whole house' protector. After all, a surge must be earthed
before it can enter the building - regardless of how interior
wiring is installed. For example, two wire receptacles or
three wire? Makes no different. The surge is earthed at
service entrance - at single point earth ground - regardless
of what types of outlets and wiring are inside.

However, if utilities enter at different locations and / or
use separate earth grounds, then this wiring can adversely
affect the household surge protection 'system'. The incoming
wiring - not interior wiring - is important for effective
protection.

JAD wrote:
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" decided to spread more crap by writing in
message ...
Richard Freeman wrote:
Wrong the reason I know Telco Surge protection is no defense
against near or direct strikes is that I have seen Time and Time
again surge protection literally blown off the distribution frame
(where it has been installed) and equipment on those lines dead
following near or direct strikes.

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?

how big then I have certainly seen 1 Joule MOVs destroyed - yes
with short Earth leads to the mains/Switchboard earth stake


So where does Richard find this 1 joule MOV? Even tiny MOVs
costing less than $0.05 are 30 joules. Radio Shack sells a
small MOV that is 70 joules. And yet neither would be
sufficient for 'whole house' protection. Richard says he saw
a 1 joule MOV destroyed because he invents this number. Where
does he find a 1 joule MOV? He does not even know basic
numbers. Even undersized power strips start on the order of
300 joules!

Richard Freeman posts "1 joule" because he was challenged to
post a number. So he had to invent that number. He argues
incessantly without technical knowledge. He demonstrates no
knowledge of electricity beyond installing PA systems. Using
junk science reasoning, he must avoid or invent his numbers -
such as a mythical 1 joule MOV.

If Richard had technical knowledge, then he knew even 100
joules was grossly undersized. But his (mythical) surge
protector was damaged by a surge. Of course. 1 joule surge
protector would be grossly undersized - quickly destroyed -
and therefore useless. No wonder he claims surge protectors
don't work. He tries to stop a flood with a sponge!

Did his mythical protector have a short connection to
earth? Of course not. This earthing requirement was
completely new to him. Suddenly that mythical 1 joule MOV is
now provided:
with short Earth leads to the mains/Switchboard earth stake.

oh gee look at that the efficacy of the earth ( a point I have picked w_tom
upon time and time again) now gets mentioned

Why would he install a 1 joule surge protector with a short
connection to earth when he insists that all surge protectors
are useless? When Richard finally posts a number - the 1
joule protector - it is a number that does not even exist!
Now he invents a short connection to earth ground. But the
deception continues.

oh dear ! I made a typo and left a K out what a shame! it should have read a
1K Joule protector so the only defense w_tom has is to pick on Typos.
Was it an obvious typo ? hell yes ! but w_tom never let facts stand in his
way ...

To confuse others, Richard posts half facts:
Lightning does vary in strength but is Typically between
1,000,000,000 and 10,000,000,000 Joules

And where is most all that energy dissipated? To deceive,
Richard forget to mention all of what Dr Uman says. In his
book, Dr Uman then continues:
Most of the energy available to the lightning is converted along
the lightning channel to thunder, heat, light, and radio waves,
leaving only a fraction available at the channel base for
immediate use or storage.

Maybe Richard would now like to post how many joules
actually exist at the strike location?

ahh look at that ! By posting the energy in a Lightning strike ( I was
responding to his lie that : " Lightning strikes typically are not high
energy events" at this point not even discussing what form the energy was) I
forced w_tom to do a bit of basic research instead of crapping on with his
usual fallacies and half truths ... unfortunately for him the answer to his
question still makes his claim that " Lightning strikes typically are not
high energy events" look the blatent lie it is. As a Lightning strike
typically runs to 10,000,000 Joules of electrical energy .... to quote from
the same source - note that this is a typical strike and they can be both
bigger and smaller.

But then w_tom lives on blatent lies and misrepresenting the Truth and in
fact for clarity let me re quote w_toms lie in it fullness and my response
again :

Firstly w_tom Lied thusly :

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.

to which I replied accurately :

I have given the Numbers before but w_tom has ignored them as they are too
inconvenient to his arguments but once more for the dummy :
Lightning does vary in strength but is Typically between 1,000,000,000 and
10,000,000,000 Joules (thanks Professor Martin A. Uman,Professor of
Electrical and Computer Engineering at the University of Florida,
Gainsville)

so you see I posted accurately but with a bit of judicous snipping w_tom
managed to misrepresent what I said ( I see he has stopped top posting but
his snipping is still getting the better of him)

Posted previously was this challenge:
Then Richard can tell us which component isolates modem
from AC mains surges?

Note he talks about AC mains surges here not Lightning

He responds:
It is a very simple device in use since before World War 1 called
a Transformer another very simple device which has been in use
for well over 100 years is called a capacitor

Well then all we need do is install transformers and
capacitors on all incoming wires. Then never suffer surge
damage?

This was in fact a popular effort to provide Lightning protection (not 100%
effective however) in Telephony systems

However Richard tell us that nothing can protect from
direct lighting strikes. He cannot have it both ways. Either
transformers and capacitors mean no surge damage - OR -
transformers and capacitor, like surge protectors, are not
effective protection from the direct strike.

oops he twists and turns now he claims he was talking about Lightning only
!!
btw most Transformer cores Saturate when driven at excessive voltages
effectively providing protection against over voltage surges - of course
these do have limitations such as not providing complete protection against
lightning but then again w_tom was talking about surges here rather than
specifying Lightning.

Reality: those devices have a breakdown voltage. They
become short circuits at excessive surge voltages. As posted
earlier, all appliances contain effective surge protection.
What do they use? Galvanic isolation (transformers) and
capacitors. Effective protection IF the surge is earthed
before it can enter the building. Effective internal
protection if the building uses 'whole house' protectors and a
single point earth ground.

which still fail to protect against direct strikes

In the meantime, that modem has a direct connection to one
AC main wire - in direct contradiction to Richard's post. But
then Richard never did the multimeter testing.

Ok I have now run a multimeter between a modem and the Pins on the power
plug it measures effectively open circuit - no surprise here as they are
double Insulated but then again w_tom has trouble understanding simple
concepts like double insulation, Lightning etc
Ok now a challange to w_tom please name a brand and model of modem ( name a
bunch of them in fact if it is so common) on sale today which have a direct
connection between AC mains and the internal ICs. In fact name some that are
not double insulated (this will probably be the point I discover another
American weirdness like unearthed toasters but it certainly holds true in
Australia and England and I cannot perceive why it would be different in the
USA).

That AC main
wire is why modems tend to be easily damaged by AC main
surges. AC main surge that was not earthed using a 'whole
house' protector.

This is just a blatent lie from w_tom to try to support his other Lie that
Lightning damage typically comes in via AC mains let me try once more for
the dummies :
MODEMS DO HAVE DIRECT CONNECTIONS INSIDE THEM BETWEEN THE ACTIVE OR THE
NEUTRAL TO ANY PINS OF ANY IC the only possible exception here would be one
using a switch mode power supply but of the half dozen or so I have here all
a powered off plugpacks or internal linear power supplies.
some of the Older modems that I used to service did have earth connections
to the mains earth but modern modems tend to be double insulated ( all the
new ones I have seen are but if I say all w_tom will find an exception to
the rule) and any way MEN mains earth is about the best earth you are going
to get without spending a whole lot of money

Protection using transformers exists in
appliances and in that modem. Protection that is overwhelmed
if surges are not earthed using 'whole house' protection.
But again, these are old and well proven concepts. Concepts
that Franc Zabkar has also demonstrated.


Richard Freeman has become a sounding board so that lurkers
can learn about effective and ineffective surge protectors.
So that lurkers can learn how modems may be damaged from
surges that entered on AC mains - the "No Dialtone Detected"
message. But Richard Freeman serves no more purpose to this
thread.

No I serve the purpose of pointing out the errors of w_toms fantasy lets
spell it out in simple language :

Lightning damage to modems typically enters the modem from the unearthed
phone line and leaves heading for MEN earth


He invents rather than first learns his facts. That
mythical 1 joule MOV being a classic example.

yep I admit a typo I left the K out but then again it must have given w_tom
the thrill of his life - something I was actually wrong about !

The
misrepresentation of what Dr Uman posts being another
example. The transformer and capacitor that would provide
surge protection -

Transformers typically do provide surge/over voltage protection - through
core saturation but will not provide protection against direct Lightning
strikes. They do however provide isolation for the internal circuitry from
AC mains but then again w_tom is to ignorant to even try his own test -that
of measuring between the electronics of a typical modern modem and the AC
pins with a multi meter - the 9V or so does not break down the insulation in
the plugpack as w_tom would have us believe.

Further more I never ever ever said that this provided adequate protection
against Lightning - Since he is so behind the eight ball WRT to the
principles of Electrical basics and in fact this whole argument he has to
invent fallacies then claim I made them to give him something to argue
against.

protection that 'whole house' surge
protectors and single point earth ground cannot - according to
Richard.

Yep thats right in a direct/near strike current comes from all sorts of
sources : Aerials, alarm wiring, Phone lines, building frames etc etc etc AC
mains protection is not any use at all.

Modem protection means that all incoming utility wires -
especially AC electric - must have an earth ground connection
before entering the building. Modem damaged because AC
electric had no properly installed 'whole house' protector. A
surge protector being only as effective as its earth ground.

wrong as always w_tom has trouble with facts seen time and time again by
anyone in the Telco industry - equipment damaged by Lightning entry from
phone lines.


Regards
Richard Freeman

On Tue, 16 Sep 2003 17:15:36 +1000, "Richard Freeman"
put finger to keyboard and composed:

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.

See my other post.

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 ?

.... other mains connected appliances were damaged also.

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'.

Is it valid to analyse lightning as a pure DC event? AFAICS, 1000A x 1
ohm gives 1kV, so even low ohm values could give rise to damaging
potentials. If this potential appears at the earth terminal of any
appliance, then surely that appliance would sustain damage, unless
there is no exit path for the current, in which cause the appliance
would temporarily float to this surge potential. This observation goes
to the heart of my PC question. If the entire PC, by virtue of its
numerous earth connections, floats to the strike potential, then
surely only the DAA would see the full potential difference between
the surge value on the host side and that of the distant earth on the
line side??? Wouldn't this explain the damage I observed in the two
PCs I have previously alluded to?


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

On Wed, 17 Sep 2003 13:11:05 +1000, "Richard Freeman"
put finger to keyboard and composed:

Telephone exchanges have very extensive earthing systems - this is true
All metal work in the exchange is tied to earth
Exchanges are usually fed by underground cables and enter through an earthed
metal sheath
the underground conduits near the exchange are earthed back to the exchange
earth

If I disconnect all phone appliances from the socket and measure the
voltages on each pin with respect to a GPO earth, I get 1.2VAC,
-0.3VDC on one pin and .3VAC, -53.6VDC on the other. Doesn't this
suggest that the positive terminal of the battery is connected to
exchange ground, as is depicted in my "Understanding Telephone
Electronics" primer (Radioshack p/n 62-1388, 1983)?

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.

perhaps w_tom can explain how a single strand 0.28mm square wire is going to
exhibit a lower impedance than a multi-strand 2.5mm square wire

Does lightning follow simple DC principles, or does it have an RF-like
characteristic with an accompanying skin effect? If the latter, then
that short earth conductor will have a significant impedance, and the
potential developed across it could be substantial, given that the
strike current could be of the order of 1000s of amps, as you state
elsewhere.

oops it does not not under any circumstance maybe if w_tom knew basic
Electrical theory and basic Physics he would not make these sorts of errors.
I quoted DC resistance as it is readily measurable in the examples I used
the impedance will be higher I admit but the imedance of the Mains wiring is
still going to be a fraction of the impedance of the phone line.

Note here that w_tom top posts so that people cannot take the original
statement in context and therefore see how ridiculous w_toms argument is

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.

It does ????
Which modem IC pins would they be ???

An internal modem is connected to the PC's ground, and therefore AC
ground, via all the ICs on the host side, eg the DSP and controller.
An external modem makes the same connection via pin 5/7 ot the
DB9/DB25 RS232 interface.

thats funny all ( I have found 6 so far ) the modems I have here (and a
number are made in america ) are double insulated - THERE IS NO DIRECT
CONNECTION BETWEEN ANY PINS ON ANY IC IN THE MODEM AND AC MAINS !

This is true only if the modem is not part of, or connected to a
computer.

w_tom is merely showing his ignorance again - Modems nowadays are built for
an international market and the easiest way of dealing with all the power
variations is to power the modem from a (double insulated) plugpack even
older modems which I used to Repair (that right component level repair)
which did have metal cases had no direct connection between active or
Neutral and the internal Electronics they did however have a mains earth
connected to the internal Electronics and Lightning damage was typically
between the Line interface and the Mains earth with other damage scattered
around the modem depending on how close the strike was.
Modern modems that are double insulated are effectively earthed via the
Serial cable back to the PC (every PC I have seen has an insulated case -
with the exception of Laptops) which is why damage can and often does
include damage to the DSP in the modem and sometimes the serial interface in
the PC.

I'm confused. Aren't you confirming w_tom's point?

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?

It is a very simple device in use since before World War 1 called a
Transformer another very simple device which has been in use for well over
100 years is called a capacitor

A transformer cannot isolate a lightning strike, or severe surge. How
else do you explain the failures I observed on both the primary and
secondary sides of the various PSUs in the equipment alluded to in my
initial post? And how do you expect a capacitor to isolate or protect
anything? If it's an AC surge, a capacitor will appear as a short
circuit. If it's a rapid DC surge, then both terminals of the
capacitor will initially rise to the peak level of the surge. AFAICS,
a capacitor is only useful when connected across the mains where it
can shunt differential spikes.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

On Wed, 17 Sep 2003 01:11:19 -0400, w_tom put
finger to keyboard and composed:

But again, these are old and well proven concepts. Concepts
that Franc Zabkar has also demonstrated.

Please allow me to say that I know very little, if anything, about the
mechanisms involved in a lightning strike. I am merely an interested
observer who has many more questions than answers. The limit of my
experience in this area is in assessing and repairing the resultant
damage to equipment.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

"Franc Zabkar" wrote in message
...
On Tue, 16 Sep 2003 17:15:36 +1000, "Richard Freeman"
put finger to keyboard and composed:



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'.

Is it valid to analyse lightning as a pure DC event?

Nope it is Pulsed DC and fourier analysis of a pulse reveals all sorts of
components.

AFAICS, 1000A x 1
ohm gives 1kV, so even low ohm values could give rise to damaging
potentials. If this potential appears at the earth terminal of any
appliance, then surely that appliance would sustain damage, unless
there is no exit path for the current, in which cause the appliance
would temporarily float to this surge potential.

Yep !

This observation goes
to the heart of my PC question. If the entire PC, by virtue of its
numerous earth connections, floats to the strike potential, then
surely only the DAA would see the full potential difference between
the surge value on the host side and that of the distant earth on the
line side??? Wouldn't this explain the damage I observed in the two
PCs I have previously alluded to?

Quite possibly however it does not explain the damage to the other equipment
in the house and besides my point still stands the MEN earth system and
Earth wires provide a much better Earth than that provided by the Phone line
/ phone cabling and it is more logical to assume in the case of modem/PC
damage that the surge went the other way. Especially if you had been
confronted as often as I have Surge protection blown out of the Krone blocks
they were plugged into and Lightning damage on Data lines which were
terminated at each end with line isolation Transformers. In the last 17
Years I have been in the Data comms industry I have seen too much Lightning
damage to reach any other conclusions especially when careful analysis of
the damage matches Basic Electrical Theory and the laws of Physics.

Regards
Richard freeman

"Franc Zabkar" wrote in message
...
On Wed, 17 Sep 2003 13:11:05 +1000, "Richard Freeman"
put finger to keyboard and composed:

Telephone exchanges have very extensive earthing systems - this is true
All metal work in the exchange is tied to earth
Exchanges are usually fed by underground cables and enter through an
earthed
metal sheath
the underground conduits near the exchange are earthed back to the
exchange
earth

If I disconnect all phone appliances from the socket and measure the
voltages on each pin with respect to a GPO earth, I get 1.2VAC,
-0.3VDC on one pin and .3VAC, -53.6VDC on the other. Doesn't this
suggest that the positive terminal of the battery is connected to
exchange ground, as is depicted in my "Understanding Telephone
Electronics" primer (Radioshack p/n 62-1388, 1983)?

The Power feed for a phone line is connected via a feed bridge with a DC
resistance of a couple of Thousand Ohms further more the traditional Feed
bridge is made up of Inductors - in other words it has a very high
impedance - this can hardly be considered a connection to Earth adequate to
even think about shunting a Lightning strike to earth - even before we start
thinking about the series impedance of the phone line.
Try measuring the current between the Earth and each leg of the phone line
it is typically a maximum of 20-30mA and then try measuring the resistance
to earth on the 0.3V leg - bear in mind that the impedance of this earth
will be higher (not lower) than the DC resistance.

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.

perhaps w_tom can explain how a single strand 0.28mm square wire is going
to
exhibit a lower impedance than a multi-strand 2.5mm square wire

Does lightning follow simple DC principles, or does it have an RF-like
characteristic with an accompanying skin effect? If the latter, then
that short earth conductor will have a significant impedance, and the
potential developed across it could be substantial, given that the
strike current could be of the order of 1000s of amps, as you state
elsewhere.

Lightning is effectively Pulsed DC and hence it contains all sorts of
Harmonics in fact with such high currents involved (peaking at in excess of
4500 Amps) even earth resistance becomes significant but I digress. The
question I asked was how multi strand 2.5mm square wire is going to show a
higher impedance than 0.28mm single strand (typical 0.6mm telepone wire 0.4
mm is also often used in Line cables) - it does not, no matter how you do
the sums.

oops it does not not under any circumstance maybe if w_tom knew basic
Electrical theory and basic Physics he would not make these sorts of
errors.
I quoted DC resistance as it is readily measurable in the examples I used
the impedance will be higher I admit but the imedance of the Mains wiring
is
still going to be a fraction of the impedance of the phone line.

Note here that w_tom top posts so that people cannot take the original
statement in context and therefore see how ridiculous w_toms argument is

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.

It does ????
Which modem IC pins would they be ???

An internal modem is connected to the PC's ground, and therefore AC
ground, via all the ICs on the host side, eg the DSP and controller.
An external modem makes the same connection via pin 5/7 ot the
DB9/DB25 RS232 interface.

This is true and I have never denied that the modem ends up being connected
to AC mains earth via the PC. But w_tom has claimed that ICs in the modem
are connected directly to an AC electric wire - not an AC Earth wire - and
this is the point I am pulling him up on.

thats funny all ( I have found 6 so far ) the modems I have here (and a
number are made in america ) are double insulated - THERE IS NO DIRECT
CONNECTION BETWEEN ANY PINS ON ANY IC IN THE MODEM AND AC MAINS !

This is true only if the modem is not part of, or connected to a
computer.

Again this is true but that was not the claim that w_tom made, he stated -
"A direct connection exists between some pins on modem ICs and one AC
electric wire." this is ludicrous to say the least.
The MEN earth is tied to Earth at the Switchboard at each House it enters
and this earth is connected together via typically 60 Amp multi strand Cable
which is then connected to the equipment via 2.5mm multi strand cable - this
provides a far better earth than a single Earth stake as a Single earth
stake in the event of a direct strike will go to typically 50,000V above
earth potential this is known as EPR or GPR.
If you were a Lightning strike hitting power lines which path would you
take? (assuming you dont just follow a flashover down the insulator) Through
a modem to a relatively high impedance earth through relatively high
impedance wiring. or through the Mains Distribution system via (compared to
the phone line) relatively low impedance cabling to an earthing system
distributed over a number of earth stakes.
On the other hand if you were a Lightning strike hitting a phone line where
would you go ?

w_tom is merely showing his ignorance again - Modems nowadays are built
for
an international market and the easiest way of dealing with all the power
variations is to power the modem from a (double insulated) plugpack even
older modems which I used to Repair (that right component level repair)
which did have metal cases had no direct connection between active or
Neutral and the internal Electronics they did however have a mains earth
connected to the internal Electronics and Lightning damage was typically
between the Line interface and the Mains earth with other damage
scattered
around the modem depending on how close the strike was.
Modern modems that are double insulated are effectively earthed via the
Serial cable back to the PC (every PC I have seen has an insulated case -
with the exception of Laptops) which is why damage can and often does
include damage to the DSP in the modem and sometimes the serial interface
in
the PC.

I'm confused. Aren't you confirming w_tom's point?

Nope as his point was : "It only takes a multimeter. A direct connection
exists between some pins on modem ICs and one AC electric wire."
Firstly he used the term "AC Electric wire" and said nothing about an Earth
also he claims the connection is in the modem itself he does not mention the
interface or the PC it is plugged into.

BTW I noticed anothe typo I made I should have said "(every PC I have seen
has an earthed case - with the exception of Laptops)" w-tom obviously missed
it.

w_tom has probably heard this statement made by someone who was referring to
the modem getting an earth via the serial interface and with his very
limited understanding of the issue under discussion has taken it completely
out of context and is merely highlighting his ignorance on the subject of
Lightning and Lightning damage.

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?

It is a very simple device in use since before World War 1 called a
Transformer another very simple device which has been in use for well
over
100 years is called a capacitor

A transformer cannot isolate a lightning strike, or severe surge.

w_tom was talking about surges he did not mention either Lightning strikes
or severe Surges in this question.

How
else do you explain the failures I observed on both the primary and
secondary sides of the various PSUs in the equipment alluded to in my
initial post?

I had reassesed my original reading through the body count you gave. It
seems the house in question most likely received a very close or Direct
Lightning strike resulting in current flowing through the wiring and metal
work (including gutters etc) to the handiest earth point - which would have
been that provided by the MEN mains - in many instances through the PSUs of
equipment plugged into the Mains.

A picture of a direct strike in action BTW can be found at :
http://wvlightning.com/gscenic.html
There is a bit of religous guff but have a look through the Pictures and
speculate as to how w_toms MOV would have offered 'Complete protection' to
equipment in that house.
This claim of 'Complete protection' from a single 1KJ MOV on the AC mains
btw is what I object to most from the lies that w_tom keeps spouting.

And how do you expect a capacitor to isolate or protect
anything? If it's an AC surge, a capacitor will appear as a short
circuit. If it's a rapid DC surge, then both terminals of the
capacitor will initially rise to the peak level of the surge. AFAICS,
a capacitor is only useful when connected across the mains where it
can shunt differential spikes.

aha ! you obviously have a much better understanding of Electronics than
w_tom whos postings merely serve to highlight his ignorance of basic Physics
and Basic electrical theory and practise. You are right of course and the
Cap will not provide protection in the case of extreme surges but then again
I read w_toms question to refer to surges in general. Hold that thought
however and lets see what w_tom comes up with :-).

Regards
Richard Freeman

Ohh Bugger I seem to have scared off w_tom ..... Just when he was getting so
amusing too

Richard Freeman wrote:

Ohh Bugger I seem to have scared off w_tom ..... Just when he was getting so
amusing too

Just mention cheap ATX power supplies, and he'll be back lugging his 3 1/2 digit
multi-meter! Maybe a 1 Joule surge supressor as well.

Virg Wall
--
Somewhere, something incredible is waiting to be known.

~ Carl Edward Sagan ~