[Towertalk] creating ground "surround" of house: Obstacle
Guy Olinger, K2AV
k2av@contesting.com
Thu, 19 Sep 2002 00:33:08 -0400
Evaluate the grounding needs by considering the currents that flow and
THAT ARE INDUCED during a lightning strike.
If lightning hits the tower, ALL conductors will either conduct direct
or induced current away from the tower.
This includes the tower, both shield and inner conductors of all coax,
and all miscellaneous conductors.
The lightning induced current on the coax shield and inner conductor
will be of the same phase, or longitudinal current.
Grounding of coax shields to the tower ground at the base of the tower
will lower the shield current away from the tower to some degree, but
the lightning is looking for ANY path away from the tower to dissipate
the charge. The idea here is that the (hopefully) lower surge
impedance of the tower ground system will accept more current and the
coax shield less. But it won't get it all.
Some IS headed for the shack on the shield of the coax.
If you ground the shield of the coax at the entry to the house, this
will shunt some to whatever ground system you have attached at the
entry point.
If that entry ground is NOT connected to the house ground, you will
raise the ground of your shack above the potential of the house safety
ground, and route the lightning through the house to equalize against
the power ground. This happens because the entry ground and the coax
shield to the rest of the shack are a parallel circuit.
If you did it right and you have a single point entry (or a separate
entry properly tied to the) house ground, then you ALREADY HAVE tied
the tower ground to the house ground. Via the coax shield.
If the coax is large diameter hardline, it will probably handle it. If
it's a single RG8 size coax, it's a bit on the small size and you
might do some bad things to the coax, including create pinholes in the
jacket, which will cause the eventual destruction of braided coax by
admitting moisture.
The best thing is to extend the tower ground to the house ground with
something good enough to carry the current.
My 110V electrical line to the tower is an outdoor ground-fault
breaker at the tower. It is grounded to the tower and the tower
ground. Read the National Electrical Code and treat the tower like an
outdoor swimming pool.
73, Guy
----- 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."
>
> _______________________________________________
> 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
>