Protecting 1Gb Ethernet From Lightning Strikes

Wed Aug 14 11:02:25 UTC 2019

Subject: Protecting 1Gb Ethernet From Lightning Strikes Date: Tue, Aug 13, 2019 at 02:22:12PM -0400 Quoting Javier J (javier at advancedmachines.us):
> I'm working with a client site that has been hit twice, very close by
> lightening.
> 
> I did lots of electrical work/upgrades/grounding but now I want to focus on
> protecting Ethernet connections between core switching/other devices that
> can't be migrated to fiber optic.

If lightning comes so close that it will break things inside the same
facility because they are connected by structured cabling, two things
typically have failed;

* The building as such is not adequately protected.

* There exist too large potential differences within the electrical
  system inside the building.

For #1, telecoms regulations on site grounding and protection give good,
albeit expensive advice. The most important part is that all cabling
enter the facility with its screens at common potential. The reason
is that most blown equipment comes from in-ground potential difference
between different cables. (I've poured shattered IC's out of a poor ADSL
router after such a strike. ) If that potential difference is cancelled
upon entry in the facility by bonding all grounds the risk is minimised.

For #2, it is mostly solved by fixing #1, but it is proper to fix it by
mesh-connecting grounds on all equipment together. If there is a 10mm^2
(around AWG7) bonding conductor parallel to the 0,14mm^2 (AWG25) drain
wire in the foil screen, which way will the current take?
Do note that star grounds are popular, but they're impossible to maintain
and typically don't work at high frequiencies, which will lessen their
efficiency against fast-rising transients. Mesh grounds are better at
conducting high frequencies and are easier to maintain.

Having several power utility feeds into same facility will of course
exacerbate the problem, which is one of the reasons it is illegal
in Sweden.

If you need to cross between two buildings, copper should be
rejected. Fiber is so much better. And pays for itself immediately upon
first strike survived.

/Måns, has 6 pairs 9/125 between garage and house at home. 
-- 
Måns Nilsson     primary/secondary/besserwisser/machina
MN-1334-RIPE           SA0XLR            +46 705 989668
I feel partially hydrogenated!
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