Hi Dale - Yes, I do disconnect at the point of entry to the shack, and
no, there was no evidence of scorching on the roof.
I was in the shack when the hit occurred, and it was very loud and
seemingly close - I'm not sure but suspect that some share of the strike
current arced across the bulkhead connectors on my panel, something I
have seen before with nearby strikes. However, nothing was visibly
damaged.
Everything active on the tower - two rotators, an antenna relay box, and
a Stackmatch - was damaged, though not vaporized. I suppose this means
that the tower's grounding took much of the energy. I thought at the
time that the hit was on my F12 40m yagi, because one of its loading
wires was broken, but it could have been on the mast a couple of feet
above it. I bet it gave the long-time-resident wasps in the mast a
headache!
73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
On 9/18/2012 10:15 PM, Dale Svetanoff wrote:
Pete,
Thanks for the detailed reply. Yes, given the second floor shack
location (which I had in my younger days), I agree with your
contention about disconnect being the most effective approach. You
validate that concept by mentioning a direct hit. My one remaining
question: Since your shack is second floor, I presume that you
disconnect the cables on the inside of the entrance panel, thus
isolating the equipment from the outside lines that could be exposed
to a direct hit and/or coupled currents. That means the cables are
still attached to the outside of the entrance panel and you mention
that the wire grounding it runs along a first floor porch roof. Have
you ever noticed any evidence of scorching to that roof after a hit?
Again, thank you for sharing details with us on the reflector.
73,
Dale Svetanoff, WA9ENA
Sr EMC Engineer
E-N-A Systems, LLC
Specializing in shielding applications, system grounding, and
lightning protection
----- Original Message -----
*From:* Pete Smith N4ZR <mailto:n4zr@contesting.com>
*To: *svetanoff@earthlink.net <mailto:svetanoff@earthlink.net>
*Cc: *rfi@contesting.com <mailto:rfi@contesting.com>
*Sent:* 9/18/2012 3:40:45
*Subject:* Re: [RFI] ISOBAR
Answers interspersed.
73, Pete N4ZR
The World Contest Station Database, atwww.conteststations.com
The Reverse Beacon Network athttp://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
On 9/18/2012 10:46 AM, Dale Svetanoff wrote:
Pete,
Two questions: 1) That 40 feet of bare #2 wire between the entrance panel
and power line ground - I assume it is run outside, and if so, how many
ground rods are on it?
My shack is on the second floor - the wire runs along a first
floor porch roof and then down the side to the existing ground rod
that also serves the main electrical panel.
2) Does the wire provide all of the grounding for
the entrance panel, or do you have one or more ground rods tied to the
panel?
See above
While I understand and agree with your comment about non-ideal
installations, I think the point has to be made that trying to accomplish
as good of an installation as possible should be a prime goal of every
radio installation design. The two most important factors, in ANY case,
are: A) Keep the lightning current on the outside of your
shack/house/vehicle; B) Design for as low an impedance as possible between
the entrance panel and earth ground and between tower (or antenna support)
and ground. Naturally, net Z will be the total of Xsub-L + wire resistance
+ bonding resistance + earth coupling resistance. Net Z should be figured
for frequencies in the range of about 100 kHz to 10 MHz, the main spectral
distribution of lightning energy. (Yes, it extends upwards to nearly 100
MHz, but at greatly reduced energy levels.)
My shack location virtually assures that I cannot achieve a
good-enough installation so that I should count on it. My
solution, which has worked so far (including a direct hit on the
tower) is to disconnect everything at the entry panel.
The latter is essential during the strike because of the huge currents
during a strike. Since all of the station equipment is tied (bonded) to
the one ground system (or should be), the lower the net Z to ground means
the less voltage developed differentially between grounded connections and
power feeds, antenna inputs, and so forth. (This is in addition to the
common mode induced currents from a strike.) Keeping the lightning
current on the outside of the building is key to minimizing what I call the
"Kingsford Effect" (conversion of a building into a pile of charcoal) and
is usually handled well by a good entrance panel, well-grounded, and
equipped with protective devices for each and every I/O line used in the
station. I can personally vouch for the effectiveness of that approach.
I contend that disconnecting the cables is probably as good as
you're going to get in my situation.
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