Thanks to all for suggestions. AC power line is indeed likeliest
ingress. I checked and there are no overvoltage clamps on the
200 m power feed from the pole; we are at the end of the line.
Grounding is excellent at our home (I did it myself, to ground
rods and building's rebars) but I never got to put in the big varistor
to clamp the feed; its a GE/Harris V275HE250 device rated at
20,000 amperes. We'll do it next week and It will sacrifice itself
during the next hit and blow the breakers. We'll also get after
the state electricity monopoly to install spark-gap protectors or
something. (Expected reply "If you're not happy with your
service we can disconnect it for you.)
Among other items damaged was the APC uninterruptible
power supply. APC replaced it for us.
Jeffrey Race
On Thu, 11 Jun 2009 14:39:04 -0600, Will Honea wrote:
>** Reply to message from "Jeffrey Race" <os2-wireless_users@2rosenthals.com> on
>Thu, 11 Jun 2009 21:34:54 +0700>
>> Further to previous msg I'd appreciate recommendations about
>> coax and ethernet protective devices (clamping devices) to
>> protect my equipment so not destroyed a second time>> jeffrey race
>
>This could get to be a long discussion - lightning problems pre-date
>electronics by centuries and the first practical lightning arrestors were the
>ones Benjamin Franklin devised in the late 1700s. First, don't even sweat the
>internal wiring like coax until you REALLY solve the external threat: your
>power lines. Those expose you for a radius of miles in some cases. Next, look
>at the building itself. Such things as aerials, chimneys, and metal gutters -
>ground those really well. You might even want to install a specific lightning
>rod and grounding mesh if your area is prone to a lot of lightning. As part of
>this, verify and test your internal power ground - I see too darned many of
>those 3rd wire power grounds that are worse than useless. Once you have done
>that, you can proceed to reduce the risks elsewhere but until you provide a
>reasonable shell around the internal equipment you are really just wasting time
>and money.
>
>When you have snubbed the environmental exposures the next step is the power
>system. Virtually all the damage I've dealt with in nearly 40 years of site
>installations entered the system through either the power line or external
>communications lines (telephone, TV cable or antennae, etc.). While structural
>strikes cause some electronic damage, you usually have bigger problems to deal
>with than electronics when they hit. The most common point of entry is the ac
>power line. Several companies make gas tube protectors which will shunt up to
>several kilojoules. These are sturdy glass and metal tubes with a gap in an
>inert gas (typically argon) which will arc to ground with a breakover voltage
>of 150 volts or so. One or more of those each lead of the power line followed
>by an isolation transformer is pretty much the best you can do. Those wall
>socket mounted to power strip jobs are useful for small glitches but they are
>really too puny to give major protection.
>
>As a compromise, I use a relatively small gas tube/inductor coil setup ( the
>manufacturer that made mine is out of business now) followed by a hefty UPS for
>the main station with smaller UPS units for the other clusters of gear. That
>has served through several nearby lightning strikes (Colorado gets more than
>its' share!) and a single UPS is a lot cheaper to replace than the whole
>system. Note: GROUNDING IS CRITICAL!!!
>
>For the phone and TV lines, I put my own gas tube shunt (minus the inductors)
>across the input lines and to ground from each side. I follow that with
>smaller MOV type shunts at the place my equipment plugs in but I don't even try
>to isolate the internal wiring. The only time I've seen problems with that was
>in a metal building where the internal leads were installed near the roof or
>walls and a strike would arc between the metal building and the wires. I can't
>recall ever losing equipment to a direct strike on internal wiring in a wood
>frame structure - it always got zapped either by proximity to some externally
>connected metal part or by over powering the protection on the input leads from
>outside.
>
>All the years of experience point to one primary target: GROUND. I can't say
>it enough for that is the single most important component of any protection
>scheme. If you have doubts, simply run a heavy copper lead - 8 ga. or so -
>between the third wire "ground " lead and a nearby cold water pipe (assuming
>metal pipes - plastic pipes are useless) every place you can. That will do as
>much to protect you as most of the cheap surge suppressors on the market and
>without a good ground even those are worse than useless.
>
>--
>Will Honea <whonea@whonea.net>
>
>
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