Re: Lightning and Switches
- From: w_tom <w_tom1@xxxxxxx>
- Date: Fri, 22 Jun 2007 21:09:30 -0700
On Jun 9, 2:40 pm, JF Mezei <jfmezei.spam...@xxxxxxxxxxxxx> wrote:
Well, since the switch has amber lights on the block of 4 ports, and
since its own main status light is also amber, I would have thought the
software would know about the problem. (and would think that some error
message would appear when you do an show interface fa0/xx for one of the
faulty ports.
...
Thanks. That was probably it then. I guess I can consider ourselves
lucky we didn't get a direct hit. The neighbours in the back whose
house is just a few metres from the pole that was hit are probably
feeling even luckier.
...
I hadn't thought about EMI for thunderstorms for that, always tought
about grounding differences for this issue.
Your description is typical of a "direct hit". How will be
explained later. From your description, surge electricity flowed
through port 10 and through the connected computer. Remember, to have
electricity; first an incoming and outgoing path must exist. Which
side was the path to earth? Makes no difference whether electronics
were powered on or off.
In another example, a plug-in protector earthed a surge through an
adjacent computer, out via network wire, into network card of another
powered off computer, out via that computer's modem, to earth ground
via phone line. We traced that surge by identifying and replacing
every damaged semiconductor.
Possible that four ports in the Cisco share a common interface
chip. ICs for such ports also come in four or eight port versions.
This is speculation that would explain why surge current through port
10 would damage ports 9 through 12. Dead body would better explain
why damage occurred.
This we do know. It was a direct strike. A second example. A
nearby tree was struck. Campers sleeping tangent to that tree did not
suffer. But two campers sleeping pointed to that tree suffered a
direct strike. Electricity flowed down the tree into earth. Up into
camper's feet and back to earth via heads. Current flows some miles
distant to electrical charges. That was a direct strike to campers
whose body provided a better electrical path.
Ethernet (communication) connections between buildings so easily
suffer damage for same reasons. Third example: one building literally
becomes the lightning rod (or tree) to conduct a surge through
ethernet cable to be earthed in other building. That path to earth is
destructive to electronics - powered on or off - because it easily
overwhelms protection already inside ethernet interfaces.
Many then assume damage is from induced surges - or EMI. Numbers
say otherwise. The concept is called GPR. Solution requires single
point earthing of every incoming wire, short, to a single point
ground. Any wire of any cable not earthed, short, by hardwire or
protector may carry destructive surges inside the building. That other
building simply acts like a lightning rod to carry surges into this
building. Damage for reasons similar to those campers.
Also at risk are four legged animals - for same reasons - a fourth
example. Properly constructed barns install an even better single
point ground - halo or Ufer ground. Single point earthing that
encircles a barn means no current will flow up a cows hind legs and
down its fore legs. This direct strike (when lightning strikes a
nearby tree) is reason for livestock deaths. Learn from that example
to install that inexpensive and effective earthing in new buildings.
However, even that earthing is useless when incoming wires are not
earthed before entering a barn or network center.
Back to the original failure. What was the incoming path of the
surge that was seeking earth ground? Autopsy of 'dead bodies' would
be useful. But finding someone with sufficient electrical knowledge is
difficult.
What we do know: surge found one earthing path via Cisco port 10 and
a computer's ethernet interface. Surge could have been incoming on
AC electric through computer, through Cisco port 10, then ... well,
could ports 9, 11, or 12 conduct to earth? What thing conductive was
the Cisco mounted on? Even furniture could have been part of an
earthing path.
We know a surge entered the building on a wire that was not 'single
point' earthed via hardware or protector. Fields do not provide
sufficient energy to overwhelm a many thousand volt protection
internal in computer and Cisco. How many thousands? Well, IEC
standards now define interface chips that must withstand 2K or 15K
volts. Again, we don't know which were inside those 'dead bodies'.
But we know EMI will not overwhelm that existing and industry standard
protection. It was a direct strike - if only just like those campers
beneath a tree.
How to prevent such damage? Well your telco have been connected to
virtually every building in town. Every building is a lightning rod
that connects surges directly into their switching computer? But
telco installed protection has been standard everywhere since the
beginning of the 20th Century. Preventing damage has been that well
understood for that long. Each incoming wire must make a short
connection to a common earthing electrode. Each wire connects via a
'whole house' type protector so that damage will never happen. Your
damage implies that well proven and properly earthed protection does
not exist in your facilities.
Little difference whether wires are underground or that lightning
struck 30 meters distant. Fifth example: an application note from
Polyphaser:
http://tinyurl.com/38v2dv
Lightning strikes somewhere across the street close
to the below grade West cable vault. ... The first line
of defense is the telco protection panel, but the panel
must be connected to a low resistance / inductance
ground. There was no adequate ground available in
the telephone room.
Those quick to speculate may instead blame damage on EMI. Too many
examples and those numbers are little understood by those who blame
EMI. It was a direct strike that overhwhelmed protection found on all
ethernet ports. Power on or off makes no difference. Solution starts
with what always defines protection - the earthing system.
.
- References:
- Lightning and Switches
- From: JF Mezei
- Re: Lightning and Switches
- From: Doug McIntyre
- Re: Lightning and Switches
- From: JF Mezei
- Lightning and Switches
- Prev by Date: data/control plane
- Next by Date: Re: Show commands
- Previous by thread: Re: Lightning and Switches
- Next by thread: Re: Lightning and Switches
- Index(es):
Relevant Pages
|
