IMHO,
Long runs of UTP  (unshielded twisted pair) make wonderful antenna systems for 
EMI and EMP which is why they are matched to differential drivers and receivers 
to reject as much common noise as they are designed to. Older and larger 
Ethernet interfaces have drivers separated from the logic components that can 
handle higher over currents and voltages that are induced on the cable. Newer, 
smaller integral designs cannot usually handle as much power as the older 
designs. 
UTP systems in industrial environments require higher performance drivers that 
handle higher currents and voltages since they are induced by large motors, 
HVAC and florescent lighting systems.
EMP (lightening) is a very wide band, high number of frequency bands signal 
with large amounts of power being induced into the systems they are impinging 
very rapidly. ITGOD (In the Good Old Days) we used to run everything through 
conduits which when properly grounded protected both power and signal circuits 
against lightning very well.

There is a very large wifi network in multiple mile long structures connected 
by underground tunnels, in the most active thunder storm zone in the country, 
some of the issues were:

• There were a number of power and grounding zones in the buildings
• There were local grounds at each of the wiring closets that all equipment in 
that zone was tied to. (Have the earth ground checked and if it they are 
corroded or no longer working, have a new earth ground field dug or tie to the 
“building steel” if it has one or more grounding points.)
• All inter zone runs were fiber
• Both PoE switches and local PoE bricks were used to power the remote access 
points to keep power drops over the utp to within design parameters.
• Some zones had switches with both fiber and PoE ports with the PoE ports 
handling local access points and the fiber ports running to smaller remote 
switches with PoE from there to the edge devices.
• If the power runs were too long and their was no local power available, 
custom cables were manufactured to increase power conductor sizes to lessen 
voltage drops
• All outside runs were in conduit and would preferably be fiber.

When I installed my first Ethernet with RG-9, I had to ground the cable at the 
center of the run and tape each end of the cable since it had almost lethal 
voltage at the either end of the Ethernet cable.

My analog circuits professor said forget this digital design stuff, it as an 
analog signal in a transmission medi(a)um.

Regards,

John (ISDN) Lee
________________________________________
From: Caleb Tennis [caleb.ten...@gmail.com]
Sent: Thursday, May 13, 2010 11:36 AM
To: North American Network Operators Group
Subject: POE switches and lightning

We had a lightning strike nearby yesterday that looks to have come inside our 
facility via a feeder circuit that goes outdoors underground to our facility's 
gate.

What's interesting is that various POE switches throughout the entire building 
seemed to be affected in that some of their ports they just shut down/off.  
Rebooting these switches brought everything back to life.  It didn't impact 
anything non-POE, and even then, only impacted some devices.  But it was spread 
across the whole building, across multiple switches.

I was just curious if anyone had seen anything similar to this before?  Our 
incoming electrical power has surge suppression, and the power to the switches 
is all through double conversion UPS, so I'm not quite sure why any of them 
would have been impacted at all.  I'm guessing that the strike had some impact 
on the electrical ground, but I don't know what we can do to prevent future 
strikes from causing the same issues.  Thoughts?

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