[ubuntu-uk] External CAT5 (subject change for change of topic)

Mark Harrison Mark at ascentium.co.uk
Fri Oct 22 18:03:08 BST 2010

Date: Fri, 22 Oct 2010 10:47:42 +0100

> From: Alan Pope <alan at popey.com>
> Subject: Re: [ubuntu-uk] Powerline Recommendations
> To: bdrake at crosswire.org, UK Ubuntu Talk <ubuntu-uk at lists.ubuntu.com>
> Message-ID:
>        <AANLkTi=EEEf3pWvvg3R2BdtmAfvJZaq8Nun6B5GP7OhM at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
> On 22 October 2010 10:44, Barry Drake <bdrake at crosswire.org> wrote:
> > I drilled throught the outside wall and have CAT5 all around the
> > outside. ?Quick, easy, fast, secure ....
> >
> ...almost certainly against building regs.. :)
> If it gets struck by lightning (a very real possibility given it's
> grounded via your PC/switch at each end, it could blow your entire
> network up.
> Armouring the cable may help though.
> Al.

I've been active in the Home Automation market, both as a hobby and then
professionally, since 1997, and have never encountered a lightning strike on
external cable.

External CAT on WALLS is very unlikely to be against building regs. Indeed,
building regs are far more likely to frown on INTERNAL risers, because of
the need to fire-break them every couple of storeys.

As far as I'm aware, it poses no more risk than, say, a satellite dish.

The way that lightning groundpaths work, the best thing you can do if you
have external ethernet is to have an external TV aerial mounted higher :-)

If you assume that any grounded point basically causes a "cone" below, that
extends out about 1m for each 1m in height, and that anything inside the
cone will broadly be safe (because lightning will have an easier path via
the higher grounded item), that's a good rule of thumb.

Actually, the biggest problem I've come across is the fact that ethernet
cable sheathing doesn't have great U/V stability - it will degrade over
about 7-10 years if it's left in direct sunlight. Hence, what we did (based
on electrician's recommendation) was to put it in some external trunking.
The sort that B&Q (other DIY sheds are available) sell for air extract is
good. Leave a vertical run with the bottom open, so that any water that gets
in will run down the insides and drip out without puddling, but use a decent
sealant where the cable goes back into the house.

If anyone needs pictures, contact me (Mark AT Ascentium DOT co DOT
-the-country-code-for-this-list ) and I'll mail some JPGs over.

If you are very paranoid, then of course you need to be aware that ethernet
is tappable, so if you have reason to believe that the security services are
interested in your data, then you may want to keep those runs internal :-)

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