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Lightening damage

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rcbenedict1545

Lightening damage

I’m sure there are others with more expertise on this subject then me, however several texts including the new ARRL grounding book say it may be dangerous to disconnect antenna coax in the house. It should only be done outside.
My daughters vertical was hit by lightening and the lightening leaped 5 feet from a cable on the floor to a power outlet.
Ray
W8LYJ

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k6dgw

Re: Lightening damage

Nearly every direct strike will fry something (or manythings), connected
or not. An arc that could involve a kilometer or two probably isn't
going to be deterred by a meter or so of disconnected coax. The
grandson of my Elmer in the early 50's [who now holds his Grandpa's
call] became a lightning scientist.

His advice: Very little [if any] electronic equipment will survive a
direct strike on your antenna. There are many 10's of thousands of
amperes dashing around, and lightning arcs very often fork and take more
than one path in what appears to be random fashion. For non-direct
hits, this electrical mayhem all still creates EMP's. The goal is to
have everything conductive in your shack to float at the *same*
potential. This means bonding everything together. Connecting that bond
to an earth electrode is problematical. If you do, that electrode
should be bonded to the one at the service entrance [which more often
than not is a UFER electrode in most late 20th and 21st century
construction].

Disconnecting outside can be helpful in some cases. However, my good
friend Tom, K5RC, who operates the Comstock Memorial Station near
Virginia City NV, with 7 [or so, I haven't counted lately] towers, some
well over 30 m, notes: "Lightning will just as likely strike a 1 meter
sagebrush bush as a 47 meter tower with a 3-el 80 meter yagi at the top."

That said, in the rare times when we had close lightning while living in
the foothills of the Sierra Nevada, I did the disconnect at the base of
the tower out back.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 11/6/2017 4:12 PM, Gmail wrote:

> I’m sure there are others with more expertise on this subject then me, however several texts including the new ARRL grounding book say it may be dangerous to disconnect antenna coax in the house. It should only be done outside.
> My daughters vertical was hit by lightening and the lightening leaped 5 feet from a cable on the floor to a power outlet.
> Ray
> W8LYJ
>
> Sent from my iPad
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K9MA

Re: Lightening damage

I agree that disconnecting the coax from the antenna inside the house is
a bad idea. All my cables from antennas are permanently connected to a
well-grounded and bonded panel in the shack. I disconnect the coax and
control cables from that panel to the radio. Now, if the tower takes a
direct hit, that panel, the ground system for the station, and all the
equipment may go to many thousands of volts above earth ground, because
even my 13 ground rods don't have all that low an impedance. However,
everything in the station should stay close to the same potential. And,
by disconnecting the equipment from everything except ground, there
isn't a direct path for current to flow THROUGH the equipment.

The hazard, of course, is that there could be an arc from that panel or
the station "ground" through the floor or wall of the basement to earth
ground. That's why it would be better to have that disconnect panel
outside by the tower 20 feet from the house. However, having to slog
through the snow at 20 below in January would discourage operating.
(And we do sometimes have lightning in January in Wisconsin!) It's a
trade-off I've chosen to make. I suppose I could put the antenna
relays, etc. in a box outside, and disconnect it there in the summer,
and have a second disconnect inside for winter. At this point, however,
that outside box would have to get past the aesthetics committee, and
she's none too happy with the tower in the first place.

About bonding: Lightning is not DC, and the inductance in any conductor
more than a meter or so long can be significant. All you can do is to
try to minimize the bonding inductance by using short, wide conductors.

In the 28 years my tower has been up, it has not yet taken a direct hit,
though it could in the next thunderstorm. I've had no damage from
nearby strikes.

I think lightning IS more likely to strike a tall tower than a short
bush. Using the "cone of protection" concept, I'd expect the
probability of a strike to go up as the square of the tower height. It
seems as if lightning which, if the tower weren't there, would have hit
the ground within the circle at the base of that cone, is likely to hit
the top of the tower instead.

73,
Scott K9MA

--
Scott K9MA

[hidden email]

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Richard Fjeld-2

Re: Lightening damage

In reply to this post by rcbenedict1545

I'm trying to avoid taking anyone's side on this discussion. I wanted to say that I worked for a company that had towers throughout the state which were several hundred feet tall. Over the years, I only saw one that took a hit. The company was so certain their grounding specs had not been followed, that they made the contractor dig up the entire grounding layout. It revealed the specs had not been followed.

Certain radio and TV services need to operate 24/7 and can't shut down when lightening threatens. Their grounding methods apparently prevent the towers from being hit .

Rich, n0ce

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Gmail
Sent: Monday, November 6, 2017 6:12 PM
To: [hidden email]
Subject: [Elecraft] Lightening damage

I’m sure there are others with more expertise on this subject then me, however several texts including the new ARRL grounding book say it may be dangerous to disconnect antenna coax in the house. It should only be done outside.
My daughters vertical was hit by lightening and the lightening leaped 5 feet from a cable on the floor to a power outlet.
Ray
W8LYJ

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Igor Sokolov-2

Re: Lightening damage

In reply to this post by K9MA

I had a direct lightning strike this summer in July. It has also caused
fire that created more damage then lightning itself. The interesting
thing is that lightning hit not the 20 m tall grounded telescopic mast
that had no antenna (it was down for service), but rather metal roof of
a shed that was only 2 meters high and 1 meter away from the tower. The
the mast was up for 20 years and never before had been hit, although
there were many lightning strikes hitting the neighborhood.

73, Igor UA9CDC
07.11.2017 7:08, K9MA пишет:

> I agree that disconnecting the coax from the antenna inside the house
> is a bad idea. All my cables from antennas are permanently connected
> to a well-grounded and bonded panel in the shack. I disconnect the
> coax and control cables from that panel to the radio. Now, if the
> tower takes a direct hit, that panel, the ground system for the
> station, and all the equipment may go to many thousands of volts above
> earth ground, because even my 13 ground rods don't have all that low
> an impedance. However, everything in the station should stay close to
> the same potential. And, by disconnecting the equipment from
> everything except ground, there isn't a direct path for current to
> flow THROUGH the equipment.
>
> The hazard, of course, is that there could be an arc from that panel
> or the station "ground" through the floor or wall of the basement to
> earth ground. That's why it would be better to have that disconnect
> panel outside by the tower 20 feet from the house. However, having to
> slog through the snow at 20 below in January would discourage
> operating. (And we do sometimes have lightning in January in
> Wisconsin!) It's a trade-off I've chosen to make. I suppose I could
> put the antenna relays, etc. in a box outside, and disconnect it there
> in the summer, and have a second disconnect inside for winter. At
> this point, however, that outside box would have to get past the
> aesthetics committee, and she's none too happy with the tower in the
> first place.
>
> About bonding: Lightning is not DC, and the inductance in any
> conductor more than a meter or so long can be significant. All you
> can do is to try to minimize the bonding inductance by using short,
> wide conductors.
>
> In the 28 years my tower has been up, it has not yet taken a direct
> hit, though it could in the next thunderstorm. I've had no damage
> from nearby strikes.
>
> I think lightning IS more likely to strike a tall tower than a short
> bush. Using the "cone of protection" concept, I'd expect the
> probability of a strike to go up as the square of the tower height. It
> seems as if lightning which, if the tower weren't there, would have
> hit the ground within the circle at the base of that cone, is likely
> to hit the top of the tower instead.
>
> 73,
> Scott K9MA
>

rcbenedict1545

Re: Lightening damage

In reply to this post by Richard Fjeld-2

I worked in Broadcasting for over 55 years. It’s common for broadcast towers/antennas to take direct hits. The lightening protection systems deflect the energy to ground. AM stations use ball gaps at base of each tower. In the mid 70s I worked at WKBN and lived in a farm house in the middle of 6 400 ft towers. We would sit on the front porch and watch tower #2 take hits in almost every storm. I remember only one time when there was damage, connector blew off end of 3” line.
There were lightening panels on top of towers so, the hits could be counted.
Ray
W8LYJ

Sent from my iPad

> On Nov 7, 2017, at 00:19, Richard Fjeld <[hidden email]> wrote:
>
> I'm trying to avoid taking anyone's side on this discussion. I wanted to say that I worked for a company that had towers throughout the state which were several hundred feet tall. Over the years, I only saw one that took a hit. The company was so certain their grounding specs had not been followed, that they made the contractor dig up the entire grounding layout. It revealed the specs had not been followed.
>
> Certain radio and TV services need to operate 24/7 and can't shut down when lightening threatens. Their grounding methods apparently prevent the towers from being hit .
>
> Rich, n0ce
>
>
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On Behalf Of Gmail
> Sent: Monday, November 6, 2017 6:12 PM
> To: [hidden email]
> Subject: [Elecraft] Lightening damage
>
> I’m sure there are others with more expertise on this subject then me, however several texts including the new ARRL grounding book say it may be dangerous to disconnect antenna coax in the house. It should only be done outside.
> My daughters vertical was hit by lightening and the lightening leaped 5 feet from a cable on the floor to a power outlet.
> Ray
> W8LYJ
>

George Danner-2

Re: Lightening damage

In reply to this post by Richard Fjeld-2

Rich,
Even massive grounding systems do not keep a tower from being hit! It only
mitigates the damage.

I was CE of a TV station in South Florida with towers of 1,000' a couple at
500' and several more at 100' to 200'. They all got hit at one time or
other. Sometimes many times a year.
We used massive grounding systems with the tall towers. The towers we rented
or on buildings - we had to take what we got. Some were excellent some were
non-existent.

We operated 24/7 since 1955. We did have redundant equipment. We had two-way
antennas as high as 900', microwaves from 100' to 950'. Tower cameras as
well. The ENG receive sites (at 950' & 500') had very sensitive LNAs at 2, 7
& 13 GHZ. as well as the pan/tilt steering electronics and drive systems.
When possible we did not put electronics on the tower; because of the surge
current of a direct strike.
A small (tiny?) strike will have over a thousand amp current surge. If the
steel tower has a 0.1 ohm resistance, then the top of the tower is 100 volts
above the bottom. Any electronics at the top that is connected at the bottom
can have that potential on the equipment case (a DC ground loop so to
speak) of 100 volts. Most times it is much higher.

The least affected equipment were the microwave transmitters and receivers
that used waveguide. The signal up and down the waveguide is transmitted
rather then conducted.

We felt that the best money we spent to mitigate lightning damage were
dissipation arrays on all of our towers higher than surrounding structures.
Over a 10 year period our lightning damage costs were reduced significantly
over the 10 year period prior to that installation. It seems that
dissipation arrays are in dispute at this time.
It goes to the old adage - that just because you put out elephant repellent
and then see no elephants still does not mean the elephant repellant works!

My 40 years experience in South Florida as a Broadcast Engineer has taught
me that you will find the weakest links in your plant's structure and make
them less vulnerable but never be completely immune to lightning damage
unless you eliminate all conductors of electricity. Fiber interconnections
between studios and towers really helped us reduce the losses.

73
George AI4VZ

-----Original Message-----
From: Richard Fjeld
... Certain radio and TV services need to operate 24/7 and can't shut down
when lightening threatens. Their grounding methods apparently prevent the
towers from being hit .

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Jim Brown-10

Re: Lightening damage

On 11/7/2017 9:31 AM, Gmail - George wrote:
> Any electronics at the top that is connected at the bottom
> can have that potential on the equipment case (a DC ground loop so to
> speak) of 100 volts. Most times it is much higher.

It is a serious mistake to view lightning as DC. While there MAY be a DC
component, lightning is primarily an RF event. IEEE studies show that
the energy in lightning is (very) broadly centered around 1 MHz. As far
as lightning (and any other RF) is concerned, that tower is an antenna,
and must be understood as an antenna.

It is also a serious mistake to think of our antennas as the only means
by which lightning enters our homes. Lightning comes in on power wiring,
telephone wiring, and CATV wiring. It also induces current on wiring
within our homes.

It is VERY common for lightning currents induced on wired Ethernet
cables, connected to equipment with shunt mode surge protectors (MOVs)
to fry computers (especially their Ethernet circuitry) in the loop that
includes their green wires back to the panel. This happens in homes and
offices with no radio antennas at all.

All of this is why the most important element of lightning protection,
BY FAR, is proper bonding of all equipment and grounds in a building.
This is all covered in considerable detail in N0AX's new ARRL book on
Grounding and Bonding for hams. It is of FAR greater value than all the
surge protectors you could possibly buy. And you can get most of the
same information for free from these slides.

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC

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