Protecting ethernet cables from effects of lightening FREE cabling and networking Helpdesk
 Question by Char posted 01 Aug 2003
 Protecting ethernet cables from effects of lightening
a few months ago, we had a terrific (horrible)
lightning event that was so sever that, even
though you couldn't see if anything was actually
hit, it blew out our garage door sensors, fried
the GFI outlet in the garage, took out our cable
modem, network switch, WAP's ethernet port, and
various other network connection points --
USB, ethernet, and parallel. This, despite the
fact that we had turned off and unplugged
everything but we had left all the various cables
connected. If I had been using SHIELDED Cat5e
cables, would that have protected them from
behaving so badly in response to what must have
been some atmospherically propagated EMP?

 Answer by Dmitri Abaimov posted 23 Aug 2003
Dear Char,

It's difficult to tell for sure, but the result might be even worse with shielded cable since the shield will have to be grounded, and in a regular residential building there is usually only one point of grounding - electrical power ground. This point would surely take the hit, and some of the charge could even propagate through to your ground-bonded equipment, like your PC's metallic case, for example. So, even if you would unplug the PC's power, there will be still a path to electrical ground through the NIC's connection to the cable's shield.

So, the bottom line is: shielding a cable is not a solution to lightning problem.

Dmitri Abaimov, RCDD

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