[TowerTalk] FW: Near Field Lightning Damage

[Matt]

No one else has offered up anything so thought I would throw in my 2 cents
worth...    Draw out a 1-line schematic of your station equipment set-up.
Show ALL of the wiring connections.   Include all house wiring (lights,
telephone, cable, intercom, alarm system, etc...   )  When you think you
have all the wiring identified, go back and recheck again.   Draw a box
around your station representing the room where the station is located.
Every metal line (or pipe) that crosses that box must be equalized quickly
to the common point ground potential during a lightning event, as well as
the chassis of the equipment shown inside the box.  "Quickly" means the
protective devices are either mounted directly to the common ground or by
means of a very short, low impedance ground strap.   Implementing this is
usually not a trivial matter.  But, when you do achieve this, the potential
of all the interconnected equipment will rise and fall at approx. the same
rate during a lightning event.   It works.   Check out W8JI's web page on
lightning protection for more info.

Sorry for your equipment loss and hope this suggestion helps.

Matt
KM5VI


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
Kenneth Goodwin
Sent: Thursday, April 16, 2015 4:32 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Near Field Lightning Damage

Doubt if this is correct forum but I need some assistance.  I've lost two
desktop computers and some radio equipment in the last three years having
experienced near-field lightning damage (hits ~ 1/4 mile or less away into
the ground or power/cable lines that discharged into the ground, damage was
not parted thru the power or cable lines).  I believe the damage mechanism
is between the USB connections to the radio equipment and the other USB
accessories associated with the computer system - wireless keyboard/mouse,
scanner, Davis weather system, etc.)  Potential difference between the radio
equipment USB interfaces (radio equipment single point ground) and the
computer accessories (house a/c power ground)?  The computer case is tied
into the radio single point ground system (bus wire).  The radio system's
single point ground is tied directly to the house's power ground with a big
bus wire between the two grounds so not a perfect single point ground but
the best I can do unless I move the 200 Amp service over to the other side
of the house.  The antennas are routed thru an extensive single point ground
system full of ICE and PolyPhasor devices, all equipment is on an UPS (three
APC 1500 VAC units running everything except a KW linear).  Three levels of
surge protection starting at the power line drop to the house including the
cable and telephone interfaces.  The hit in 2012 took out the motherboard on
the computer and ALL of the USB radio and rotator interfaces that were
connected to the computer.  I thought I would stop this from happening again
by providing antenna disconnects right after the single point ground.  So
the damage this week occurred with ALL of the antennas/rotator/control lines
physically disconnected.  The lightning hit sounded far away from the house.
No radio interfaces were damaged but the motherboard exploded (big snap)
when I was using it.  The computer's power supply checked out OK but the
computer will not power on.  An active (amplified) USB line from the
computer to one of the radios was nailed but not the radio's usb port.  Only
thing I can think of is to isolate the radio-computer interfaces by using an
ESD protected USB hub.  Or just a dedicated computer for the radio equipment
that I could easily disconnect.  Any suggestions or where I can find a
shoulder to cry on will be greatly appreciated.  Ken K5RG

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