More ADSL/Phone Wiring Qs

[The Natural Philosopher]

I think that what constitutes a 'direct srike' is at issue.

I have seen power cables take a direct strike and survive..never a 50 pair overhead.

Most so called 'direct strikes are not to the actual wires, but to places very near by. Yes you can get several tens of KV, and a few hundred milliamperes..but its not the same as a Mv at 5 amperes!

There is enough impedance in the overhead line for it NOT to be the preferred path back to earth at the exchange of course..the exchange equipment will survive.

Its another reason BT likes to bury its cables of course..the last couple of hundred meters of overhead, even with a direct strike, won't do them any harm at all.

It will destroy anything and everything at the customer end of course.

Fortunately such *direct* strikes are rare. Mine is the only one in this country I have direct knowledge of. And that was 20 years ago. OTOH overhead power lines get struck many times in every storm..mostly they just trip and reset. Sometimes they get burned out, or insulators arc over and fail.

In Africa where serious thunderstorms happened every other day, and much wiring was above ground, it was not unusual for whole swathes of phones to be out for a day or two. They would always ring in a storm anyway.

In short indirect strikes that put a few KV on the line at a few mA are routine, and protected against by the stuff that BT puts on its own kit at their end, and what is built in at the customer end.

Direct strikes in this country are very very rare, and equipment survivability is more or less a function of how far the kit is from the strike. Mostly the strike will simply use a short section of cable which burns out to an arc, on its way to wherever it can find ground.

[John Rumm]

I realised he was talking at crossed purposes, so thought it worth commenting...

(he does have a bit of a "history" in this group for giving forceful presentation of "facts" that seem to loose a bit in translation!)

Failing that, just replace the BT master with a NTE/5 and use a faceplate on it. Note the compatible faceplates are usually better than the ones BT usually fit, since they often have a wired output for the unfiltered signal as well.

[w_tom]

My comments were based upon what was observed in the UK where a 'faceplate splitter' was in the room; not on a master socket.

JohnDW defines faceplate splitters, instead, only located one on the master socket. JohnDW's post apparently clarifies that confusion.

In addition to the XTF sockets shown in

are other devices used in UK that does same filter function and called a microfilter. In North America, same devices are just called filters; come in a wide variety of configurations from dongle like microfilter to faceplate replacement types. Most American installations put the filter adjacent to a POTS phone since additional losses due to 'stubs' and 'antenna noise' on twisted par wire is typically trivial; in most situations.

Described was how I had changed some American installations to duplicate the 'faceplate splitter on master socket' electrical circuit

- to learn from experience. Yes, it will reduce noise and distortion. But in most every case, those advantages were not quantifiable. For example, twist pair wire made DSL frequency noise irrelevant.

Puting the faceplate splitter on Master Socket is an electrically superior soution.

[David Hansen]

On Tue, 23 Jan 2007 09:42:45 GMT someone who may be "Brian Sharrock" wrote this:-

My installation is in Scotland and is typical of what the Post Office did in the 1960s.

Another house in the family in a different country, England, has an underground telephone connection all the way to a little box inside the front door. It is typical of 1980s installations. Other houses in the family in the same village have overhead or underground telephone connections, depending on when they were built.

I doubt if new estates will be built with overhead telephone connections, but where there are new houses in an older area, or a house in an older area is getting a new telephone line, these will come off the existing poles rather then a new cable being laid. Seems sensible to me.

One can spot similar eras in other connections to houses.

[w_tom]

Two golfers sought shelter during a thunderstorm when lightning struck a nearby tree. Golfers suffered a direct strike when lightning went down tree, up one golfer's leg, down other, and then on through earth to distant charges. Golfers suffered severe direct strike due to a concept called GPR. Golfers are encouraged to keep feet together during storms; to create a single point connection to earth.

Same problem is why cattle and other four legged creatures are killed by a direct strike when lightning strikes a nearby tree. A direct strike conducts that current through the animal or object.

Polyphaser, a legendary company for protection, also describes a direct lightning strike to communication equipment in a nearby building:

Lightning strikes somewhere across the street close

More than 95% of trees that suffer direct strikes do not suffer appreciable damage as even a US Forestry Service study determined. Direct strikes are not just the 'so rare ones' that permenantly scar a tree. Numerous direct strikes need not leave obvious indications.

All are examples of direct strikes. Average direct strike distributes about 20,000 amps. To protect from lightning, a minimally sized 'whole house' protector for AC electric is 50,000 amps. That protector and other earthing paths (other dwellings, ground wire on pole, transformer earthing, etc) earth that transient which is why a direct strike to one building may average less than 20,000 amps.

Telcos bury wires before those wires get to COs for many reasons including a connection to the underground vault of 'whole house' type protectors. That cable must first enter the underground vault so that all wires can be earthed via protectors. Only then the cable emerges into the building; well separated from switching computer.

But as demonstrated in a 1950s Bodle and Gresh study published in the Bell System Technical Journal, some 100 strikes were recorded to each cable (underground and overhead) over 5 month period.

The typical homeowner should expect maybe one serious direct strike every seven years. This number will vary significantly and is typically much less in UK. However the number also varies significantly even within same town due to underground conditions such as a nearby pipeline, conductive rock formations, etc. Being atop a hill or in a valley makes little difference. In fact, sides of a mountain may be more often struck then its top. More important are geological conditions.

How important would be even better earthing or a longer lasting (higher joule) protector? Neighborhood history is one factor to consider.

Point is that direct strikes to household electronics can even occur when different utilities share different earthing electrodes. Like cattle and those golfers, a nearby strike to a tree would then be a direct strike to equipment inside the dwelling. Down tree, up one ground electrode, across house destructively via household appliances, down other electrode, then onward through earth. Human saw a direct strike to a tree. He learned later it was also a direct strike through his appliances because dwelling was not constructed using a single point earthing electrode.

Just another example of a direct strike.

[tony sayer]

Step distance its called!...

Yes storms seem to follow rivers according to a local yokel who knows more about country matters than most all;!..