Re: [SLUG] Splitting Cat 6 cable

From: Donald E Haselwood (dhaselwood@verizon.net)
Date: Thu Oct 19 2006 - 22:34:00 EDT


On Thursday 19 October 2006 22:12, Paul M Foster wrote:
> Eben King wrote:
> > On Thu, 19 Oct 2006, Chuck Hast wrote:
> >> On 10/19/06, steve szmidt <steve@szmidt.org> wrote:
> >>> Plus it will not be susceptible to any interference. Now you can have
> >>> as many connections as you want. (Once you buy the fiber optics
> >>> nodes, which you should be able to do for a few hundred each. Then
> >>> the switch to allow multiple connections. Plus the fiber tool which
> >>> is only a few hundred. Of course the cable which is not too bad when
> >>> you get a volume break.)
> >>>
> >>> But then you'll be sitting pretty! Imagine! One of the few who
> >>> already have
> >>> fiber to the home!
> >
> > [...]
> >
> >> I have my home on one end of my property and
> >> my workshop/offfice/junk place on the other end with about 300 ft
> >> between them. I have buried 1.5 inch pipe and run cat 5 through it, but
> >> of course a lighting storm took out the hub on one end (spared the other
> >> though)
> >
> > Yeah, outdoor conductive LANs in Florida are contraindicated for just
> > that reason.
>
> You'd think that galvanized pipe would "solve" the problem by minimizing
> the voltage difference between the two points. Of course, if you run
> PVC, you'd have to run a ground wire through it and ground it thoroughly
> at each end.
>
> (Yes, I know that lightning can still strike and be transmitted
> regardless. I'm just sayin'...)
>
> Paul

The pipe with the cable inside forms a transmission line and the transient
induced from a lightning strike will be very large even though the cables and
pipe are grounded at both ends. The pipe helps a lot, but surge protection
is still needed (and at both ends). It is the transient that wrecks things.

The IEEE standard for the *average* lightning strike (10% of the strikes will
be ten times as large) has a rise time of the current of roughly 2E9
amps/sec, which when multiplied by the (small) inductance of a 100 feet of
pipe puts one up in the tens of thousands of volts.

So far (knock-on-wood, etc.) I have eliminated nearby lightning taking out my
switches/hubs/router/nics by putting an ethernet surge suppressor on each nic
and each of the router ports. They cost about $20-25 each, so I skip the
switches/hubs figuring they are cheap to replace.

Don
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