[RFI] ISOBAR

[Pete Smith N4ZR]

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 at contesting.com>
>     *To: *svetanoff at earthlink.net <mailto:svetanoff at earthlink.net>
>     *Cc: *rfi at contesting.com <mailto:rfi at 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.
>