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Re: CAT5 surge/lightning strike protection recommendations?

  • From: Marshall Eubanks
  • Date: Wed Sep 14 09:53:46 2005

On Wed, 14 Sep 2005 08:44:16 -0400
 "Steven M. Bellovin" <> wrote:
> In message <>, "Robert E.Seastrom" writes:
> >
> >
> >Todd Vierling <> writes:
> >
> >> Seriously, though, that's exactly what you're describing, and about what I'd
> >> suggest in a no-other-option scenario -- but if it's possible to pull fiber
> >> through the conduits, it would probably be far less expensive long term, or
> >> even medium term if the physical fiber spools can be bought cheaply enough.
> >
> >For those who haven't priced the stuff lately, in spools of 1000' the
> >per-foot prices of 2-strand MM tight buffered fiber suitable for
> >pulling in conduits like he (hopefully) has tends to be
> >price-competitive with cat5 on a per-foot basis.  Extra strands are
> >cheap; the pricey part of fiber is the jacket and strength members;
> >even super-pure glass is not that expensive overall.
> >
> >The expensive parts in the equation turn out to be the termination
> >trays and connectors.
> >
> Also the labor of pulling it, when there's already something in the 
> (shudder) ground.
> My direct experience with running long-distance underground cable is 
> dated -- let's put it like this; we were dealing with RS-232 -- but the 
> countermeasures to a direct strike on copper cables don't seem to have 
> improved nearly enough...

I don't think they will... tens of megavolts is hard to protect against.

This depends a little on where you are. I have experience with cable runs  in Southern
Florida (where lightning strikes can occur daily), West Virginia and Virginia (with strikes common)
and Hawaii (where they don't seem to  be as frequent). The cable may be in the ground, but
it is connected to stuff at either end which isn't, and given the potential differences that
occur in the natural environment (~ 150 volts per meter of altitude), this means that cable runs
can act like lightning rods connected directly to your network gear.

So my jaded perspective is that you WILL get hit if you connect buildings
with copper, and you WILL NOT like it. Since this can be entirely mitigated through the use of
fiber, use fiber if you possibly can.


> 		--Steven M. Bellovin,

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