Re: Could a telephone line damage a modem ?

Before one can learn why modems are damaged and how to avoid
damage, first, one must establish some well proven principles.

Electricity means a complete circuit. That means
electricity must first have an incoming and outgoing path
through each device in a circuit. Myths would have you
believe a surge enters on phone line, damages a modem, then
stops. Reality - first a transient forms a complete circuit
through that modem. Only later does something in that circuit
fail.

Second, the destructive transient seeks earth ground. Ben
Franklin demonstrated the concept in 1752. Lightning would
find earth ground through a wooden church steeple. Franklin
simply shunted (diverted, connected) lightning to protection.
Was protection the lightning rod? Of course not. Protection
is the earthing system.

This is how transients damage modems AND how electronics
damage is routinely avoided. BT has a £multi-million computer
on their side of the same wire. That computer is connected to
wires all over town. Why is that computer not damaged?
Because they install what you don't have. They earth (shunt)
all incoming lines through a 'whole house' protector.

In the US, phone lines are routinely protected by a 'whole
house' protectors installed free on the NID (the US equivalent
of a master socket). A protector so effective and so
inexpensive as to be installed on every incoming phone line.
Some products that do that:

http://www.one.co.uk/catalogue/telebyte/LightSurgeProtect/22PX.HTM
http://www.keison.co.uk/furse/furse11.htm
http://www.oneac.com/pdf/917116c.pdf

But again, the protector is not protection (except where
myths are promoted). The protector is only a shunt (a
temporary connection) to protection. Earth ground is the
protection. Distance to earth ground is also important.

To install equivalent, you must install a protector so that
it will shunt (ground) a telephone line 'less than 3 meters'
to the same earth ground also provided by incoming cable and
AC electric. This single point ground is essential to
household electronic protection. This single point ground is
what ineffective plug-in protectors avoid discussing to
protect sales. Pictures from professionals demonstrate the
earth ground 'system':

http://www.erico.com/public/library/fep/technotes/tncr002.pdf
http://www.cinergy.com/surge/ttip08.htm

Notice that even a buried wire can carry a destructive
transients into household electronics. Every incoming line -
not just telephone line - must be earthed to protect that
modem. Earthed either by a 'whole house' protectors (AC
electric and phone) or by a direct hardwire connection (cable
TV and satellite dish). Single point earthing is protection -
what ineffective and overhyped protectors avoid discussing.

We confirm a destructive circuit by repairing modems.
Typical damaged area is modem's DAA section. Sometimes a PNP
transistor that drives the off hook relay. This particular
failure creates the "No Dialtone Detected" message. Or modem
'hangs' the telephone line when computer is powered. Why is
that transistor damaged? It was in a circuit from cloud to
earth ground.

One final point. Those advocating nearby 'fields' as a
reason for damage never provide numbers for their
speculation. Numbers have been posted elsewhere. Bottom
line: electronics damage is a direct strike. A direct
electrical connection to a line far down the street or a
direct strike to something nearby and buried in the ground.
But to have damage, an electrical connection - a complete
circuit - is made through electronics (which is also why some
electronics are damaged whereas others are not). All
appliances (even modems) have internal protection. Protection
that may be overwhelmed IF the building does not earth every
incoming utility.

Protection is earth ground - not the hyped plug-in power
strip and UPS protectors. That protector is only as effective
as its earth ground. Earth ground - what ineffective
protectors avoid discussing and provide no dedicated (less
than 3 meters) connection to.

jdr.smith@xxxxxxxxxx wrote:
> My parents live in the country probably about five or more mile from
> their telephone exchange, This is approximate so don't quote me on
> that..
>
> In the last couple of years I have manged to provide them with my old
> hand-me-down PC's.
>
> Equipped with a modem they first went in around about two years ago.
>
> My mother dials up the internet via the modem and surfs the web..have
> used several different ISP's Wanadoo, BT etc etc
>
> Now here's the interesting part...
>
> They're currently on their eighth modem !
>
> The first one lasted about two-three months and then just would no
> longer access a dial tone. I think this was a PCi Rockwell based 56K
> modem. I'd used it for about three years without any trouble.
> I put its failure down to just one of those things and replaced it with
> a PCi 56K USRobotics.
>
> This lasted about two months before that too went the same way.
> Apparently starting to drop the call at first, then would not dial any
> longer just like the first.
>
> I replaced it with an Intel PCi modem which itself lasted about
> two/three months.
>
> This pattern continued with our getting ever more suspicious.
>
> Along the way the PC has changed three times and we have also changed
> the extension cable three times.
>
> The basic telco cable run is from the apex of the roof outside their
> bungalow where it is delivered from the pole across the road.
> It attaches to the stonework relatively close to the mains electrical
> wires from the nearby eletrical lines again from poles.
> It then travels down the wall about a meter or two fairly close to
> these electrical wires before they part and go their different ways.
> The telco line then enters the house and goes to the BT master socket.
> The first telephone is plugged in here and an extension line then goes
> off upstairs to the second telephone in my fathers office.
>
> >From here there is a triple splitter, the second phone running off the
> first socket and a third phone line which runs down to the living room
> from the second socket and from the third socket a line runs down to
> the computer room where it is split between a fourth phone and the
> modem in the computer.
>
> We checked indoors and none of the internal wiring in the house runs
> near any internal domestic power lines.
>
> We've also disconnected discontinued use of the fourth phone in the
> computer room two modems ago. So that didn't seem to help.
>
> All in all it would seem that something is slowly damaging the modems
> which after several months use renders them inoperable.
>
> When I bring them back to my house to test them they won't work here
> either.
> You cant hear the relays click open/close when you first switch the PC
> on, which you normally can hear when they used to work.
> Once they have failed they are completely silent at switch on as if the
> relay has frozen up.
>
> Two of them that I gave over to them were working here at my house for
> some condsiderable time before I gave them to them to use.
>
> They expired in the same fashion in a matter of a couple of months.
>
> My parents say that although they have experienced the odd storm,
> nothing radical, the modems failures do not appear to coincide with
> these events at all and my mother religiously unplugs everything during
> stormy weather, in fact the PC is only plugged in when they use it.
>
> I've been told that it is possible to get inductance from outside power
> cables which could transfer itself onto the telco wires which could
> then feed back into the modem and slowly damage the circuitry. Is this
> possible ?
>
> BT don't seem to want to know and flatly refute the suggestion that the
> telco wires may be too close to the incoming electrical wires.
> My parents don't see eye to eye with BT at the best of times, they have
> had endless problems with the telephone line to the house over the last
> thirty or so years. Mostly due to the telco run running through the
> branches of may trees on the way to where my parents live, causing
> havoc in wet weather.
> That said BT moved the telegraph poles around five years ago so that
> the wires no longer get caught in the braches !
>
> How can I check the internal sockets to see if there are spurious
> voltages present ? Obviously it is probably something releativly slight
> or perhaps not always present ?
>
> Have they got too many devices on the line ? all the phones are REN1.
> They only have three telephones and the modem now.
>
> The current modem is another new US Robotics 56K installed today and is
> working fine, though it'll only be a matter of six or seven weeks
> before it fails no doubt !
>
> Any advice would be much appreciated, I know modems don't cost much but
> its starting to get a bit silly.
>
> thanks
>
> Jim.
.