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? 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?
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.)
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.
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 <n4zr@contesting.com>
> To: <rfi@contesting.com>
> Date: 9/18/2012 6:36:02
> Subject: Re: [RFI] ISOBAR
>
> I use a piece of 3/4 inch copper pipe running along the rear of my desk
> as a ground bus. All of my radios, computers etc. are fed off a single
> branch, and each is grounded to the pipe by a short, direct copper
> wire. The copper pipe is connected to my aluminum entry panel, and from
> there #2 solid copper goes to my power-line input ground.
> Unfortunately, that wire has to be around 40 feet long, so I know it's
> not ideal. Not all of us can have purpose-built shacks with perimeter
> grounds and copper strap galore.
>
> 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 9/17/2012 10:47 PM, Jim Brown wrote:
> > On 9/17/2012 7:14 PM, Pete Smith N4ZR wrote:
> >> I guess what I was asking was whether the snubbing at the power entry
> >> would allow MOVs to work for the branch circuit protection a
> >> cost-effective share of the time. I have experienced problems with
> >> Ethernet EMP pickup, but so far my cascaded MOVs have done the job,
> >> even when I took a direct hit on my tower.
> >
> > Not if there are the multiple ground point issues with stuff plugged
> > into the MOV box.
> >
> > 73, Jim
> > _______________________________________________
> > RFI mailing list
> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
>
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|