comp.dcom.xdsl NewsGroup Archives: Re: ADSL Surge Protection

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From: w_tom@my-deja.com
Date: Sat Sep 16 2000 - 16:44:02 PDT

 1) A telephone line sharing a conduit with AC power is a direct
violation of NEC standards.

  2) If that much current were flowing inside the house, then forget
about induced currents.  There are surge currents going to every ground
while destroying every electronics appliance.  Induction between
separate telephone lines and electric lines is quite small.

  3) Many assume that a phone line device was destroyed by a telephone
line surge.  It is rare for anyone to understand that phone lines have
effective surge protection.  It is rare for anyone to understand that
an electric line surge uses a telephone line (as one of many paths) to
earth ground.  Whether the common assumption was stated here is
irrelevant because so many others make that common assumption.

  4) Minimal protection goes a long way to protecting modems and other
appliances.   We don't need extragent protection.  Homes are still
wired as if the transistor did not exist.  Simply installing basic
ground and 'whole house' surge protector on each service goes miles to
improve simple appliances protection.  We don't even have that simple
protection in most houses.

  Hell.  About 2 of 10 older homes I visit don't even have NEC required
safety grounds properly connected.  No earth ground means no effective
surge protection.  These structures don't even have an ineffective
earth ground connection.  Furthermore many will advocate those 'three
light' outlet testers to prove a good ground.  Are the blind leading
the blind?  Only valid test for earth ground is visual inspection.  IOW
forget extreme protection.  Most structures don't even have simple
surge protection (power strip surge protectors don't even qualify as
simple surge protection because they are that ineffective).

  5) UL497A, if I remember, does not address surge protection.  However
all electrical appliances must have some surge protection (see ATX
power supply spec).  In a previous post, I KISSed (kept it simple).  In
reality, effective whole house electric surge protection only lowers a
surge to the 500 V region - which is below what any decent electronic
appliance can withsatnd.  IOW of course there are appliance standards
for surge protection - and the 'whole house' surge protection lowers
destructive surges to less than appliance transient specs.

  Sound complicated?  Yes.  I simplified the whole topic because most
readers still think a plug-in surge protection will stop or absorb a
surge - they have that little technical knowledge but plenty of

  Modems have about 2000 Volt isolation transformer.  Therefore a modem
is destroyed because the electric service did not lower surge voltage
below 2000 volts (again oversimplified so that I don't have to explain
the rest of the circuits and did not provide typical wire impedances).
Whole house type surge protection works because a surge that enters the
house is signficantly reduced if the surge is shunted direct to earth

  Better grounding, such as Ufer type grounds, were installed in a
standard home but are not utilized because we still construct as if the
transistor did not exist.  Go figure.  Better grounds mean more
effective whole house surge protection.  We install those grounds and
still don't connect to those better earth grounds.

  You want a ""network "surge suppressor" that ... lets the DSL signal
through""?  It was already installed in your telephone premise
interface before xDSL existed.   They are also available at component
level from (I believe) http://www.semtech.com  and
http://www.gensemi.com  and from Teccor (Sidactor).

  However you can never get the same ground as AC circuits because
every foot of wire is an electronic component - not a shorting
conductor.  Even electricans don't understand the concept.  That less
than 10 feet from fuse box to earth ground rod is 4 ohms reactive
impedance.  Your ohm meter may say 0 ohms but to lightning, that ground
rod and fuse box are separated by an electronic component - the 4 AWG
copper wire.

In article <DAPw5.3355$ks.90333@newsread1.prod.itd.earthlink.net>,
  "H.W. Stockman" <stockman3@earthlink.net> wrote:
> <w_tom@my-deja.com> wrote in message
>>   If lightning were that dangerous, then all operators would
>>remove their headsets and stop working until the storm has
>>passed.  Telephone exchanges would often be crashed for days
>>replacing lightning damaged electronics.  Neither happens
>>because lightning is not the powerful
>[My guess: companies that depend heavily on continued performance
>through storms also invest more heavily in protective equipment
>(compared to the average homeowner).  E.g., I worked for a company
>that had extensive networks of steel-covered copper rods driven
> into the ground, with lightning arrestors all over the roof.]
>but the more significant point...
>I don't think anyone here has claimed the lightning-related
>surges on telephone lines are necessarily coming through the
>TELCO connection to the main service.  One concern is that the
>sheer length of telephone line in a house (often using the same
>conduits as AC wires) allows it to act as an effective antenna,
>even if the connection to the TELCO is severed.  High energy
>transients through one wire can induce current in the dataline;
>static elecricity buildup during a storm can dissipate through a
>dataline.  I don't think the UL would waste so much time on
>standards for dataline protection (e.g. UL 497A) if this were
> a pure fantasy of the surge suppression industry.
> For many of us, it would just be nice to assure that the modem
>has the same ground as the rest of the AC circuits in the
>system.  If I can find a network "surge suppressor" that meets
>that simple requirement, and lets the DSL signal through, I'll
>be closer to happy.

Sent via Deja.com http://www.deja.com/
Before you buy.

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