Hi Chip,
Ref your input, "
> ...., IMHO, just running a long THHN wire between grounds is
> not enough to prevent equipment damage. "
I'm not sure how to interpret that remark, but just want to be sure that you
or anyone else does not think that my ref. to the THHN tie between grounds was
in and of itself a panacea for damage prevention. In addition to many OTHER
prevention measures, it is academic that a separate station ground be employed
and tied back to the entrance panel ground. I'm pretty sure you agree, based
on your other astute input.
Tnx, Steve K1PEK
DAVIS RF Co
>
> Message: 6
> Date: Tue, 4 Jan 2011 13:44:38 -0500
> From: Charles Coldwell <coldwell@gmail.com>
> Subject: Re: [TowerTalk] WHOLE HOUSE SURGE/LIGHTNING PROTECTION -resp.
> DAVIS RF Co.
> To: Stephen Davis <sdavis@davisrf.com>
> Cc: towertalk@contesting.com, k1ttt@verizon.net, jim.thomas@telus.net,
> garyschafer@comcast.net
> Message-ID:
> <AANLkTinXNqMTHa=iQBm1gYraNf_e9UVg+-NtvqDNk+mT@mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> On Tue, Jan 4, 2011 at 11:45 AM, Stephen Davis <sdavis@davisrf.com> wrote:
>> ?and I find that often when a single point ground was used, close to the
>> station, what was missing was the return from that back to the entrance
>> panel ground. ?This is such a simple undertaking....usually a # 6 or # 4 THHN
>
> I recently bought a house that has the main electrical panel at the
> front (grounded to a water pipe) and had (past tense) both OTA and
> satellite TV coax coming from the antenna/dish through the back of the
> house. The 75 ohm coax runs were grounded with a rod driven into the
> back of the house, and there was a long long #6 or #4 THHN wire
> running from that grounding block at the back of the house to the
> panel at the front.
>
> What's wrong with this picture? Well, that long run of #6 or #4 has
> an inductance. That inductance becomes an impedance at high
> frequencies during a lightning strike, which means that the voltage
> potential at the panel ground and the coaxial ground could differ as
> K4FMX said, "Sometimes by many thousands of volts!"
>
> That voltage difference between the coaxial ground and the panel
> ground will appear across the electronics that are connected to both
> grounds: i.e. the satellite receiver and television that are both
> plugged into the wall and connected to the antennas. Voom!
>
> Once again, as K4FMX said, "This means that ALL equipment and lines
> connected to that ground system must rise together to avoid damage."
>
> That is why, IMHO, just running a long THHN wire between grounds is
> not enough to prevent equipment damage. Yes, it is a short circuit at
> DC, but don't let that fool you. Lightning is an impulse with all
> kinds of high frequency components!
>
> Chip
>
> --
> Charles M. Coldwell, W1CMC
> "Turn on, log in, tune out"
> Belmont, Massachusetts, New England (FN42jj)
>
> GPG ID:? 852E052F
> GPG FPR: 77E5 2B51 4907 F08A 7E92? DE80 AFA9 9A8F 852E 052F
>
>
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> End of TowerTalk Digest, Vol 97, Issue 14
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