[Towertalk] creating ground "surround" of house: Obstacle
Bill Hider (N3RR)
n3rr@erols.com
Wed, 18 Sep 2002 23:51:47 -0400
Jon,
Generally, most large acreage ham stations do not tie everything together.
That's why you hear that these stations frequently get lightning hits that
wipe out equipment.
Now to your other point:
The one big thing you're leaving out is the surge induced Voltage into the
coaxes/control wires (though they have lightning protectors on them) and
house AC/TELCO/CATV wires outside the house.
As lightning travels through wires/towers, etc, a magnetic field builds up
and, when the lightning goes to ground at the tower, energy will then be
induced by that magnetic field into nearby wires that are not grounded well
or are at a different ground potential from the tower, like the list I just
cited. When this happens, bang, your equipment sees it. In fact, we often
refer to this as "not a direct hit". "Not a direct hit" is a frequent cause
of lightning-induced equipment burnout. In fact, the "not a direct hit"
could have been quite a ways away from your house and raise the Voltages in
your AC/CATV/TELCO wires enough to burn out equipment.
That's the big reason to tie all of these grounds together with a ground
grid around the house and a ground grid that emanates from each leg of your
tower(s) and then tie them together. You should also tie things like chain
link fences, airconditioners, and other outdoor equipment to this ground
grid so that any induced Voltage into these devices does not create a
difference of potential and/or induce still other Voltages into your
equipment.
You need to read PolyPhaser's book that I've often cited in these
discussions on the TT reflector.
And you need to look at my website if you haven't yet done so. I show my
example in great detail with many references and drawings/photos.
73,
Bill, N3RR
www.erols.com/n3rr
----- Original Message -----
From: "Jon Ogden" <na9d@speakeasy.net>
To: "Bill Hider" <n3rr@erols.com>; <towertalk@contesting.com>;
<brewerj@squared.com>; "Glenn Little" <glittle@awod.com>
Sent: Wednesday, September 18, 2002 11:04 PM
Subject: Re: [Towertalk] creating ground "surround" of house: Obstacle
> OK, I am willing to be educated here on this whole issue. And as I new
> tower owner, I guess I should be. Here is how I have seen things:
>
> 1.) Ground tower to ground via network of ground rods.
> 2.) Use surge/lightning arrestors in all lines.
> 3.) Don't need tie the tower to the electrical ground.
>
> My reasoning (and what I've heard others say) on point 3 is that first of
> all, that ground line could be very long. Do guys that have their towers
> spread out on 5 acres run grounds between all towers and then to their
> house? Perhaps they do and I am sure someone can answer that.
>
> Secondly, if the tower is well grounded and you have a surge protector
> grounded at the tower, why do you need to tie it to the electrical ground?
> If a strike hits the tower, the energy is shunted to ground. Any energy
on
> the center pin of the coax gets shunted to ground via the surge arrestor.
>
> Glenn mentioned that the potential between the tower ground and service
> ground could be different in a strike. That's quite possible, but with
the
> surge arrestors in place, how would the energy get from one spot to the
> other? My assumption is that the tower ground would raise in potential
> during a strike above the house ground. This would then cause the current
> flow toward the lower potential "if" the path is less reactive and
resistive
> than the path toward the lowest potential nearby. The odds of that being
> the case even with a surge arrestor seem small to me. Perhaps I am
missing
> something. Additionally, I would think you would want to keep all that
> energy away from your house ground.
>
> I am willing to be educated so fire away.
>
> 73,
>
> Jon
> NA9D
>
> on 9/18/02 9:36 PM, Bill Hider at n3rr@erols.com wrote:
>
> > I totally agree Glenn and was about to reply to Jon's response with a
> > similar answer, except I saw your comments and yours are right on.
> >
> > On another point:
> > I disagree with the theory of disconnecting equipment from the
coaxes/cables
> > as a good method to avoid lightning problems in lieu of providing a
proper
> > grounding system. Disconnecting equipment, as I have pointed out
> > previously, with some disagreement from others ;-), opens your
house/shack
> > up to arc-over at the open connections and possibly resulting in fire.
I've
> > had my antenna farm and lightning protection system in place since 1994
with
> > all equipment continuously plugged-in with out any problems. A properly
> > designed and installed lightning protection system will allow you to
keep
> > your station on-the-air 24x7, as I do. 4 Packet radios, IC-4KL, IC-781,
> > PCs, more. All antennas are always connected to both radios and ring
rotor
> > controllers. I operate in all kinds of wx, and ignore it as an
operating
> > issue. Lightning storms approach my tower/property and literally go
around
> > the property, often splitting (or morphing) so as to avoid my tower and
> > property, then re-converging and proceeding when past the property.
It's a
> > very interesting site. In a big storm, where there's lots of lightning,
it
> > looks miraculous.
> >
> > Skimping on this lightning protection stuff just doesn't make sense to
me -
> > never has.
> >
> > Bill, N3RR
> > www.erols.com/n3rr
> >
> >
> > ----- Original Message -----
> > From: "Glenn Little" <glittle@awod.com>
> > To: "Jon Ogden" <na9d@speakeasy.net>; "Bill Hider (N3RR)"
<n3rr@erols.com>;
> > <towertalk@contesting.com>; <brewerj@squared.com>
> > Sent: Wednesday, September 18, 2002 6:00 PM
> > Subject: Re: [Towertalk] creating ground "surround" of house: Obstacle
> >
> >
> >> If the grounds are not tied together, you will get a difference in
> >> potential between the two grounds. If the grounds are tied together,
the
> >> difference of potential will be minimum. If everything is tied together
> > and
> >> a lightning strike occurs, everything elevates to the same level and
> >> everything is happy. If the grounds are not tied together and a strike
> >> occurs, the two "grounds" will elevate to different points. A
difference
> > of
> >> potential and current flow. Not at all good. If the tower takes the hit
> >> (probable) and is connected to the house by anything conductive and the
> >> house is not at the same ground potential as the tower, dammage will
occur
> >> as the energy attempts to equalize. To ground the tower to the house
> >> requires ground rods placed along the path at twice the distance of the
> >> ground rod length. The ground wire should be bonded to the rods along
the
> >> path. To be done properly, the rods are driven to about 18 inches below
> >> grade and the ground wire (#2 AWG or larger) is trenched to the depth
of
> >> the rods and welded. References for this are Motorola's R-56 manual for
> >> site selection and MIL-HDBK-419A.
> >>
> >> In my past job, I evaluated sites for lightning probabilities. If
> >> everything is bonded together, minimum damage during a strike. I
anything
> >> was not attached to the system bonded ground, it was usually toast
after a
> >> strike.
> >>
> >> YMMV.
> >>
> >> 73
> >> Glenn
> >> WB4UIV
> >>
> >> At 06:42 AM 9/18/02 -0500, Jon Ogden wrote:
> >>> on 9/16/02 11:56 PM, Bill Hider (N3RR) at n3rr@erols.com wrote:
> >>>
> >>>> Now, sometimes the tower is located so far from the shack (house)
that
> > the
> >>>> impedance in the coax shield
> >>>> over that long run (say several hundreds of feet) is so large that
> > you'd
> >>>> think the lightning would dissapate before
> >>>> it got to your shack. Well, maybe it would and maybe it wouldn't.
> > Why not
> >>>> be safe and provide a path for the lightning
> >>>> that YOU know is the one you want it to take? Add that measure of
> >>>> protection. In your case, 70 ' just doesn't come
> >>>> close to being far enough to ignore this, in my opinion.
> >>>
> >>> This whole thing seems to be a bit of debate between people. To
connect
> > the
> >>> tower to the house ground or not to.
> >>>
> >>> Most people I have talked to do not connect the tower ground to house
> >>> ground. The simplest reason, is you want to keep lightning strike
energy
> >>> AWAY from the house. A big, long wire connecting 70 feet or more of
> > length
> >>> is going to have a lot of inductance to lightning and won't do much
good
> >>> anyhow.
> >>>
> >>> The reason for tying electrical grounds together is for safety reasons
as
> >>> you want all "ground" points to be at the same potential relative to
the
> > hot
> >>> wire in the electrical circuit. Otherwise, you can create major
problems
> > as
> >>> ground is not always "ground." Tying electrical grounds together
fixes
> >>> that.
> >>>
> >>> This is a different purpose for the tower ground. In fact, I
personally
> >>> think that keeping the ground separate is a very good thing as you
want
> > to
> >>> keep al lightning strike AWAY from your house electrical system.
> >>>
> >>> The best protection of shack and equipment is as one person said to
> >>> disconnect everything. Sure, but it's not always practical. So the
> >>> alternative is to bite the bullet and drop the big bucks for surge
> >>> suppressors. One of the guys that helped me put up my tower told me
in
> > no
> >>> uncertain terms to do this. He said EVERY line coming from the tower
> > going
> >>> into the house needs to be protected. The surge arrestors should be
as
> >>> close to ground as possible and grounded right near the tower.
> >>>
> >>> So yesterday I ponied up the big bucks and spent the money to get the
> >>> arrestors for every line. Cable Experts sells the ICE, Alpha Delta
and
> >>> Polyphaser models. The ICE ones that I bought cost $40 to $46 each
and
> > look
> >>> to have a pretty good design.
> >>>
> >>> 73,
> >>>
> >>> Jon
> >>> NA9D
> >>>
> >>> -------------------------------------
> >>> Jon Ogden
> >>> NA9D (ex: KE9NA)
> >>>
> >>> Life Member: ARRL, NRA
> >>> Member: AMSAT, DXCC
> >>>
> >>> http://www.qsl.net/ke9na
> >>>
> >>> "A life lived in fear is a life half lived."
> >>>
> >>> _______________________________________________
> >>> Self Supporting Towers, Wireless Weather Stations, see web site:
> >>> http://www.mscomputer.com
> >>> Call 888-333-9041 to place your order, mention you saw this ad and
take
> > an
> >>> additional 5 percent off
> >>> any weather station price.
> >>> _______________________________________________
> >>> Towertalk mailing list
> >>> Towertalk@contesting.com
> >>> http://lists.contesting.com/mailman/listinfo/towertalk
> >>
>
>> -------------------------------------------------------------------------
-
> > -
> >> Glenn Little glittle@awod.com QCWA LM 28417
> >> Amateur Callsign: WB4UIV wb4uiv@amsat.org AMSAT LM 2178
> >> QTH: Goose Creek, SC USA (EM92xx) ARRL TAPR
>
>> -------------------------------------------------------------------------
-
> > -
> >>
> >>
> >> _______________________________________________
> >> Self Supporting Towers, Wireless Weather Stations, see web site:
> > http://www.mscomputer.com
> >> Call 888-333-9041 to place your order, mention you saw this ad and take
an
> > additional 5 percent off
> >> any weather station price.
> >> _______________________________________________
> >> Towertalk mailing list
> >> Towertalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
> >>
> >
> >
> >
>
>
> -------------------------------------
> Jon Ogden
> NA9D (ex: KE9NA)
>
> Life Member: ARRL, NRA
> Member: AMSAT, DXCC
>
> http://www.qsl.net/ke9na
>
> "A life lived in fear is a life half lived."
>