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Re: [TowerTalk] Vertical antennas and lightning

To: "Tommy Alderman" <>, "'Tower and HF antenna construction topics.'" <>
Subject: Re: [TowerTalk] Vertical antennas and lightning
From: "WA3GIN" <>
Date: Sun, 1 Aug 2010 16:13:58 -0400
List-post: <">>
Want to learn more... go to the site where the article below is the home 

Special Grounding at Wireless Tower Sites will Prevent 99% of all Lightning 

Abstract: The average (30kA) lightning strike will result in approximately 
$25k in equipment damage throughout most of the US .  A hilltop standard 60 
foot PCS tower can expect a hit once every fourteen years, a hilltop150 foot 
tower can expect a hit once every other year, and a hilltop 300 foot tower 
can expect 1.89 hits every year.  These lightning strike frequencies may be 
halved if on flat terrain, doubled if on the east coast, and tripled if 
along the gulf or in Florida .  If the tower and equipment building are 
grounded and communications specially protected against lightning strike 
energy, equipment damage will be virtually eliminated, no matter where the 
tower is located.

Wireless Providers

Wireless providers that own 100 towers on flat terrain (150 foot in height) 
may expect a lightning hit every four years to those 100 towers, or saying 
it another way expect 25 of those towers to be hit every year.  If you have 
designed a 5 ohm tower ground, a limit found in most wireless specifications 
and in Motorola's R56 Standard, expect an average of $25k in damage from 
each lightning hit.  In a year, your maintenance bill, from owning the above 
100 towers, is going to be $625K.  If you are one of the 'Big Seven' and own 
a 1000 towers, your yearly maintenance bill is going to be $6.0+ Million!

There is a difference between minimum design standards found in the National 
Electrical Code (NEC) and good engineering practice. The scope of the NEC 
does not cover lightning and there is not a hint of what Ground Potential 
Rise (GPR) is or does. Nor is GPR mentioned in Motorola's R56 current 
standard either!  In fact, there is no code book or published standard today 
that relates to the engineering design of equipment locations to prevent 
damage from lightning strike energy.  However, this type of information is 
available in the "Guide for Protection of Equipment and Personnel from 
Lightning", in ASCE's Journal of Performance of Constructed Facilities, 
August 2002, by E. Duckworth .


An average 30kA lightning strike will produce a 7.5kV GPR into the earth. If 
you do not have a grounding system that is properly designed to bleed off 
lightning strike energy, you will be part of that average yearly loss 
mentioned above. In addition, if you have not isolated wire-line 
communications that entered your tower site, a grounding system of near zero 
ohms will not help either! Proper grounding and proper isolation go 

If those 100 towers would have be properly grounded and isolated, you would 
not have had a $625K maintenance bill for the year or $6,250 per tower in 
lightning maintenance damage every year. This is quite a maintenance cost to 
your company that does not have to exist at all.

Engineering Design

Design a total site grounding system that centers around a single point 
ground.  A single point ground is an absolute must for equipment protection 
against a lightning induced ground potential rise (GPR).  Without a tower 
site single point ground (SPG), equipment damage from lightning will be a 
perpetual problem.

Soil resistivity measurements must be made at the tower and building 
location in order to design a grounding system that will meet lightning GPR 
specifications. Available real-estate, soil conditions, physical location, 
typical weather for the area all needs to be taken into account.

The tower ground and building ground should be designed to be less than two 
(2) ohms each and the combined total ground should be less than one (1) ohm. 
These measurements must be made prior to connecting the power multi grounded 
neutral (MGN) to the grounding system.

The tower grounding system design requires radial grounding (spider legs) 
that will move the lightning induced GPR away from the equipment building 
and the single point ground location.  The engineering design of a proper 
grounding system and isolation of wire-line communication facilities to 
protect against lightning induced GPR will save many maintenance dollars 
over the life of a tower site.

Last but not least, protect the grounding system from corrosion by designing 
for a 40+ year life.  Grounding systems that become green dirt over the 
years are very difficult to maintain, and understandably become very 
expensive to correct.  Of course a deteriorating grounding system also costs 
more in maintenance dollars over all of those deteriorating years.

Ernest M. Duckworth Jr., P.E., President of LPGI & Affiliates
962 Coronado Drive
Sedalia, CO 80135-8303
Fax: 303.688.5551

----- Original Message ----- 
From: "Tommy Alderman" <>
To: "'Tower and HF antenna construction topics.'" <>
Sent: Sunday, August 01, 2010 4:02 PM
Subject: Re: [TowerTalk] Vertical antennas and lightning

> This then, means that ICE lightning protectors, with their center 
> conductor
> at DC ground, are really not good protectors to use? Doesn't it also bring
> in to question the advice to connect coax shields to both the top and 
> bottom
> of a tower?
> To me, what Dave says, answers the age old question about antennas of any
> kind: 'To ground or not to ground?".
> Tom - W4BQF
> Subject: Re: [TowerTalk] Vertical antennas and lightning
> Unfortunately in this case the 'bleeding' when there is a charged cloud 
> over
> head is putting charge ONTO the antenna from the ground to equalize it 
> with
> the rest of the charge being attracted to the base of the cloud.  So it 
> make
> it MORE likely to start the upward streamer that completes the path.
> David Robbins K1TTT
> e-mail:
> web:
> AR-Cluster node: 145.69MHz or telnet://
> _______________________________________________
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