On Tue, 15 Mar 2011 21:43:20 +0100
Sascha Silbe <sascha-ml-reply-to-201...@silbe.org> wrote:
> Excerpts from Jason Hsu's message of Mon Mar 14 19:31:00 +0100 2011:
>
> > How do you protect servers from lightning? [...]
>
> Others already answered this, but I'd like to stress the fact that
> you'll need proper protection on _all_ levels. Surge protectors will
> only do what they're intended to do if coarse protection does its job
> as well and so on. Match the ("input") ratings of each protector to
> the ("output") ratings (response time etc.) of the previous protection
> level. Make sure _all_ entry points to the house are protected
> (including telephone line, broadband cable, garage lighting, etc.).
> A proper ground system is of equal importance. Jim Gettys can tell
> [1].
>
And you can still only do so much. If you get a close hit, nothing on
Earth will protect electrical equipment. Lightning does not obey Ohms'
Law, but does exotic things with voltage gradients, and will leave a
conductor when it gets bored with following it, through insulation if
necessary.
The chimney of the house next door to me was hit by a minor strike,
only a few bricks loosened. I had a TV aerial in my loft, and some
damaged roof felt showed where some of the power took a slight detour.
The front element of the aerial was bent back at 45 degrees, but there
was no other damage. The body of the coax connector of the TV set was
*not* *there*. The shell was there, and the cable ended neatly, but
there was no trace of the connector body. The coax plug was completely
unmarked.
The TV tuner and power supply were damaged. Everything in the house
which was turned on was damaged, though apparently it couldn't jump
open switches. *Neon* *bulbs* were blown. Unfortunately, I was up a
ladder at the time, about two feet from a light bulb which was also on,
and which burned very brightly for a few microseconds before expiring
loudly.
One of the power amps of my tuner-amplifier did not work, and on
investigation, I found that a speaker cable crossed the TV aerial cable,
and by looking very carefully, I could see a tiny mark on both where
they crossed.
So place your trust in UPSes if you will, but look carefully at cable
crossings, where your expensive lightning arresters can be bypassed.
Don't forget the DSL line: don't assume your router will selflessly
protect the server by vaporising. Most of my lightning damage (two
telephone answering machines, apart from the above incident) has arrived
by telephone line.
--
Joe
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