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Posted by Terry on July 29, 2007, 3:11 pm
>> Well this is still my question. What if some of the piping gets
>> replaced with PVC? It happens all the time. I see no reason to have
>> to rely on the copper in the basement as a grounding path. The CATV
>> should be bonded to the service mast.
>
> A point about code changes in the past 40 years: pipes installed by
>a plumber should not achieve electrical code grounding requirements.
>Electrical code wants its own earthing and wants its own dedicated
>bonding. Meanwhile, electrical code still demands that piping be
>bonded - so that pipes do not become energized and become human safety
>problems. That electrical source could be either inside the house or
>via city pipes. Either way, that electrical danger is made irrelevant
>when bonded to AC electrical box ground. All this grounding defined
>only for human safety.
>
> Your question is not about human safety. Your question is about
>transistor safety. That means earthing must exceed what code
>requires. For example, if cable was 'grounded' by a water pipe, well,
>was it earthed? Even that pipe length can mean grounding but not
>earthing. Sharp bends and solder joints are more reason why lightning
>will also take other, destructive, paths into the house.
>
> That is your problem. Lighting surge was permitted inside the house
>where protection inside numerous appliances was then overwhelmed.
>
> How could NICs and router be damaged? A similar example. Lightning
>struck AC electric. Surge protectors adjacent to two computers simply
>connected that surge from black 'hot' wire to many other wires into
>each powered off computer. Surge was shunted from black wire to green
>wire and through network card on two computers. Surge traveled via
>network into a third computer's NIC card. Through motherboard ground,
>out modem, and to earth via phone line. Semiconductors in network
>cards and modem replaced to restore entire system AND to trace that
>surge.
>
> Surge entered via the most common entry wire - AC electric. Surge
>found a path to earth ground via phone line. Phone line appliance was
>damaged by a surge that entered on AC electric. Surge was shunted
>into two powered off computers to find earth ground, destructively via
>a third. Surge that was not earthed before entering a building will
>find too many destructive paths. Fix one, and the surge will find
>another. Solution is always to earth that surge before it enters a
>building.
>
> A surge need only overwhelm protection in one location to then
>become a good conductor to earth. One damaged computer may simply act
>as a surge protector; destructively protecting other electronics.
>That destroyed component made a better path to earth so that a surge
>did not overwhelm protection inside other components.
>
> Once a surge is permitted inside the building, then solutions become
>too complex. Fix one potential surge problem, and the next surge will
>find another destructive path through another appliance. A surge must
>be earthed before it can even enter the building so that protection
>inside all electronics is not overwhelmed.
>
> Water pipes are typically bad grounds for transistor safety. Pipes
>are too long, too many 90 degree bends, solder joints, etc. Most
>important - each incoming wire must make a dedicated connection of
>'less than 10 feet' to the same earthing electrode. How those
>connections are installed is as critical as electrode resistance -
>short, no bends, no splices, separated from all other non-earthing
>wires, all earthing wires are independent until all meet at the
>earthing electrode, etc. A summary was posted in comp.sys.mac.comm on
>4 Jul 2007 entitled "DSL speed" at
> http://tinyurl.com/2gbgef
>
> Pipes are traditionally poor earthing connections. This made worse
>when the incoming pipe is not within a 'less than 10 foot' connection
>of breaker box and telco provided surge protector. Discussed is the
>difference between grounding for human safety verse earthing for
>transistor safety. Protection means a surge must be earthed before it
>can enter a building. CATV must make a short connection to same
>electrode that all other utilities also make that short connection to.
>Grounding to pipes (not to be confused with bonding) is not acceptable
>as it was 40 years ago.
>
> Meanwhlle above only defines secondary protection. Your modem,
>network, etc protection also means the prmary protection system must
>be inspected:
> http://www.tvtower.com/fpl.html
Wouldn't having the CATV use the service mast as their grounding point
instead of the copper piping eliminate the surge danger?
Thanks for your suggestions.
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