[Power] Lightning kills underground Ethernet too; PoE wiring/voltages non-trivial!

Sun Jan 24 02:33:02 EST 2016

There are a number of commercially-available lightning surge suppression tools for PoE/Ethernet that are considered best practices in most areas where lightning is common. Members of the Wireless ISP Association (trade group) here in the US may be able to donate a few of these; Barring that, they’re available at retail for less than $50/each, and L-COM may be willing to donate some directly.

http://www.l-com.com/surge-protector-indoor-10-100-1000-base-t-shielded-cat6-lightning-protector-rj45-jacks <http://www.l-com.com/surge-protector-indoor-10-100-1000-base-t-shielded-cat6-lightning-protector-rj45-jacks>

> Here in Lascahobas, Ben splurged and hired professionals to install solar
> panels back in 2014. The roof of the building with the battery/computer
> charging room was not stable enough, so they installed them on the roof of
> a building ~10 feet away. They ran a PVC pipe from the solar panel and
> through a hole in the charging room wall, and they placed the wire inside
> that. I think they may have also grounded (is that the correct term?) the
> solar panel itself by connecting it via wire to one of the metal rebar
> prongs sticking up out of the roof.
> 
> Would a PVC pipe protect an ethernet cable that ran between buildings too?
> Sounds like if not, an ethernet switch (to prevent electrical links, like
> Sam suggests) or a wireless repeater (to eliminate the need for cables of
> any kind) are necessary.
> 
> Thanks for bringing this issue up, Anish!
> 
> On Mon, Jan 11, 2016 at 11:39 PM, Samuel Greenfeld <samuel at greenfeld.org <http://lists.laptop.org/listinfo/power>>
> wrote:
> 
> > If you are going to use any cable outdoors or where it may be exposed to
> > the elements, getting cable rated for the desired outdoor use may be as
> > important as its speed rating.  You don't want the cables getting water in
> > them, causing interesting shorts and ground currents.
> >
> > Cables routed inside of walls/vents/etc. also often have to be one of a
> > few special types for fire safety and other reasons.
> >
> > Note that these cables types are not as flexible as the cords running into
> > your computer, so make sure not to bend them too hard.
> >
> >
> > If you can afford it, it might be worth splurging for a few Ethernet
> > switches which support fiber connections.  That way there is no electrical
> > link on the data line between buildings.
> >
> >
> >
> >
> > On Mon, Jan 11, 2016 at 11:05 PM, Adam Holt <holt at laptop.org <http://lists.laptop.org/listinfo/power>> wrote:
> >
> >> Just a quick digest below for microdeployments -- some summary excerpts
> >> for those who missed both interesting/longer discussions today:
> >>
> >>    - Power-over-Ethernet (PoE) might seem like magic cure (when
> >>    installing Wi-Fi Access Points across classrooms not having nearby
> >>    electrical outlets) but PoE is tough to get installed properly, as Tim has
> >>    discovered!
> >>    - Burying Ethernet cabling in a shallow trench between nearby
> >>    buildings seems rather popular "to the garage" (quite a number of personal
> >>    experiences are documented online) however this does NOT eliminate the
> >>    lightning problem.  What kind of trenching/equipment mitigates lightning
> >>    risks and to what degree seems to be open for debate across different web
> >>    sites (if you don't have El Chapo's tunneling team on your side, avoid
> >>    these risks using underground fiber or directional wireless/repeaters
> >>    instead ;)
> >>
> >>
> >> From: Anish Mangal <anishmg at umich.edu <http://lists.laptop.org/listinfo/power>>
> >> Date: Mon, Jan 11, 2016 at 10:32 PM
> >> Subject: Re: [XSCE] RE: [UKids] Ethernet Cable
> >> To: xsce-devel <xsce-devel at googlegroups.com <http://lists.laptop.org/listinfo/power>>
> >>
> >> Interesting insight Terry.
> >>
> >> FWIW, I did some rough testing of a homemade cantenna a couple of months
> >> ago. (Rough, because it was not a perfect Line of Sight)
> >>
> >> http://people.sugarlabs.org/anish/IMG_20150910_222141.jpg <http://people.sugarlabs.org/anish/IMG_20150910_222141.jpg>
> >>
> >> The measured gain over a omni 5dbm antennas was around 7-8 dbm, which
> >> would put the overall gain at about 12-13 dbm. Not bad for a tin can
> >> antenna made essentially from spare parts :)
> >>
> >> In theory, two of these could form a pretty stable link over a kilometre
> >> or so.
> >>
> >>
> >> ---------- Forwarded message ----------
> >> From: T Gillett <tgillett at gmail.com <http://lists.laptop.org/listinfo/power>>
> >> Date: Mon, Jan 11, 2016 at 10:29 PM
> >> Subject: Re: [XSCE] RE: [UKids] Ethernet Cable
> >> To: xsce-devel <xsce-devel at googlegroups.com <http://lists.laptop.org/listinfo/power>>
> >>
> >> Underground cabling doesn't add a lot of protection against lightning
> >> strike as George has related.
> >>
> >> One problem is that when a lightning strike occurs, there are large
> >> ground currents flowing from the point of the strike outwards.
> >>
> >> This produces voltage differences between different points on the ground
> >> - the further apart, the greater the voltage.
> >>
> >> If you stand at one point, you experience no problem. But if you straddle
> >> two points some distance apart, then you are in trouble.
> >>
> >> If you introduce a copper cable between two distant points, when a strike
> >> occurs you will see a large voltage between the end of that cable and local
> >> ground (to which the equipment is essentially connected). And your gas
> >> arrestors just try to tie it all together and so carry the current in the
> >> copper conductor.
> >>
> >> The voltages and currents produced in lightning strikes are truly awe
> >> inspiring.
> >>
> >> This is just one mechanism of failure that occurs. A lightning strike is
> >> really like a bomb going off. You can describe what happens in general
> >> terms, but the detail is extremely variable and difficult to predict with
> >> any certainty.
> >>
> >> Prevention is generally considered the best strategy.
> >>
> >> On Tue, Jan 12, 2016 at 1:18 PM, Adam Holt <holt at laptop.org <http://lists.laptop.org/listinfo/power>> wrote:
> >> On Mon, Jan 11, 2016 at 10:14 PM, T Gillett <tgillett at gmail.com <http://lists.laptop.org/listinfo/power>> wrote:
> >>
> >>> Long network cable runs are a magnet for lightning problems,
> >>> particularly if they are run between buildings.
> >>> And no amount of expensive protection equipment will save you from a
> >>> nearby strike.
> >>>
> >>> General guideline for lightning prone areas is to keep network cables
> >>> short as possible and within a single building.
> >>>
> >>> If you need to network to other buildings, consider a wireless technique.
> >>>
> >>
> >> Is shallow/quick trenching also viable?
> >> Or will rats/worms/frost destroy the cable quasi-annually?
> >>
> >> On Tue, Jan 12, 2016 at 1:08 PM, Anish Mangal <anishmg at umich.edu <http://lists.laptop.org/listinfo/power>> wrote:
> >>>
> >>>> fwiw, a simple google search reveals that these are prohibitively
> >>>> priced.
> >>>>
> >>>> http://www.blackbox.com/Store/Detail.aspx/Power-over-Ethernet-Surge-Protector-60-Volt/SP075A <http://www.blackbox.com/Store/Detail.aspx/Power-over-Ethernet-Surge-Protector-60-Volt/SP075A>
> >>>>
> >>>> On Tue, Jan 12, 2016 at 8:36 AM, Anish Mangal <anishmg at umich.edu <http://lists.laptop.org/listinfo/power>>
> >>>> wrote:
> >>>>
> >>>>> Perhaps this is slightly offtopic
> >>>>>
> >>>>> Talking to a school a few days ago up in the mountains, they had a
> >>>>> lightning strike that knocked out a bunch of electrical equipment. Are
> >>>>> there any surge inhibitors for ethernet cables, would using PoE create more
> >>>>> of these issues (i.e. the surge inhibitors probably wont work with PoE
> >>>>> stuff)? Sure inhibitors are easily available for AC power sockets.
> >>>>>
> >>>>> On Tue, Jan 12, 2016 at 3:10 AM, James Cameron <quozl at laptop.org <http://lists.laptop.org/listinfo/power>>
> >>>>> wrote:
> >>>>>
> >>>>>> PoE can be loads of fun.  The products vary considerably; both
> >>>>>> injectors, cables, and routers.  Most problems can be solved through
> >>>>>> measurements, ohms law, and power calculations.  Most problems can be
> >>>>>> pre-empted by choosing industry best practice equipment, but that
> >>>>>> raises costs.
> >>>>>>
> >>>>>> To avoid all the PoE, there's no substitute for an electrician running
> >>>>>> nice thick cables for AC.  Because these cables must meet a code, they
> >>>>>> are way thicker than they need to be for a router.  It depends on
> >>>>>> where you want to put your money.

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