I think what Steve is trying to do is avoid a major current flow from his RF
ground to the AC safety ground which can fry wiring and rigs. By tying both
grounds together, I think Bob and the Electrical Code are trying to avoid a
major voltage gradient from occurring between the RF ground and the AC
Safety Ground to avoid frying people. A person can argue the theoretical
merits of both systems.
John
-----Original Message-----
From: WILLIAM F MANSEY <WA2PVK@prodigy.net>
To: tentec@contesting.com <tentec@contesting.com>
To: <tentec@contesting.com>
Date: Saturday, March 24, 2001 05:00
Subject: [TenTec] Grounding issues.
>
>I have read various comments concerning grounds, or the lack thereof, and
am
>no longer quite as sure about my grounding system. I read, with interest,
>the comment about the NEC grounding of antenna structure(s) to the AC mains
>ground. I recall, however, another comment that recommended that the
>electric service be grounded at a single point ONLY. (generally at the area
>of the connection to the utility lines)
>I have a 40' push-up pole supporting my inverted V antenna and GP-9 VHF/UHF
>antenna. This pole is attached to a good ground rod directly. I use heavy
>braided ground strap from this point to the shack. (about 8') The coaxial
>cables for the antennas on the pole, and some others as well, come into the
>shack via "bulkhead" connectors mounted on a 1/4" thick copper plate that
is
>connected to the ground strap also. I can disconnect the rigs from the
>bulkhead connectors, and plug ground jumpers into the connectors, during
>thunderstorms. The antenna tuners and rigs are all grounded to this
>arrangement using pieces of the same grounding braid. All my equipment is
>operated from power supplies that do not ground (to the power line) the
>negative DC lead. I feel safe from lightning when the antennas are
>disconnected and grounded. Unplugging the power supplies is an added
safety
>measure. The only danger remaining would be if the push-up pole was hit
>directly. (ground or no ground!)
>I am concerned about setting up "The Mother Of All Ground Loops" if I
>connected "my" grounding system to the AC mains ground. Another concern is
>due to the nature of my home's construction. The house was built in a way
>similar to concrete swimming pools: A heavy frame of "rebar" covered by a
>heavy wire mesh which then has concrete sprayed on. This framework is
>grounded to the AC mains ground. This may sound like, and does act like, a
>Faraday Cage! (windows spoil the effect) but the main purpose was
resistance
>to hurricane force winds rather than RF turbulence!. The structure is
rated
>to withstand 200+ MPH winds. I do not think that I would have any antennas
>left after such winds but at least I should still have my shack! - and the
>rest of the house as well. Having said way too much - - - I am wondering
>what IS the correct answer? Combined or separate, and isolated, grounds?
>(this is a Ten-Tec issue because 2 of the rigs are those!)
>Any and all comment(s) appreciated. True - this is not a real Ten-Tec
issue
>BUT it IS a matter of personal safety which I feel should be discussed
until
>a measure of agreement is reached. We are heading into thunderstorm
>season -especially here in Florida - so this is a timely discussion as
well.
>( a local repeater was hit 3 times in a year and a half. 2 of the strikes
>were within 2 weeks of each other) OUCH!
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/tentec
>Submissions: tentec@contesting.com
>Administrative requests: tentec-REQUEST@contesting.com
>Problems: owner-tentec@contesting.com
>
--
FAQ on WWW: http://www.contesting.com/FAQ/tentec
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
|