1. Basics of Lightning Protection for Communication Towers
7/4/2019 1:10 AM
Basics of Lightning Protection for Communication Towers
February 2018
Jim Bacher, WB8VSU
Electronic Product Regulatory Consultant
JB Consulting
Presented by: Dr. Al Torres, KP4AQI
Although aimed at communications towers such as Ham Radio, it is valued for protecting homes as well.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. It is Broadband Electromagnetics
Lightning, What Is It?
It is Broadband Electromagnetics
Image from:

3. Characteristics Three to four pulses per strike (10 to 170 µs total)
First pulse averages about 18 kA with 98% falling between 3 kA and 140 kA
Subsequent pulses are half the current
The Dayton Ohio area has about 50 thunderstorms a year; Gainesville, FL is lightning capital in the US
If you have a 75ft tower you are likely to have one strike a year (GE Technical Training) or more
For this presentation we use 10 kA for strike energy and 10 µs rise time
Info from page 4.4 of the ARRL book on Grounding and Bonding for the Amateur Radio Operator
Dr Al Torres:
The lightning capital in the US is at Gainesville, FL. Current at 10 kA is a good number to start. Do not forget the air breakdown voltage which is about KV depending on the air pressure. Once the air break down, there is a significant power dissipation.
2. When I was measuring lightning, the strike with the most visible photometric irradiance had a rise time of 8 microseconds. The fall time was 22 microseconds with a peak at the 8 microsecond end. An eight microsecond rise is equivalent to about 125 MHz (remember that because we will use it later)
3. The Ldi/dt is very important because it only takes a tiny amount of inductance to generate a significant voltage. It you use 8 microseconds, the voltage will get worse for the same current. So parallel inductances are good.....to reduce the L.
From: ARRL book on Grounding and Bonding for the Amateur Radio Operator

4. How I learned the hard way
1984 Built a new House with builder pouring the concrete for the base of the tower
Then the neighbors showed up when they saw the tower base
And they were right, first 7 years we had direct strikes resulting in damage every year
Then I read / implemented Polyphaser’s book on lightning protection and no more damage

5. The original house config
Old School Grounding method / no Bonding
I actually found that all though the electrical service had a ground wire, it’s connection to the ground rod was buried. What I found was it was missing a ground clamp. In the case of the DARA Clubhouse it’s ground connection did not exist on the electrical service.
Image from the 2016 ARRL Handbook Page 28.8 figure 28.6 Copyright ARRL

6. Proper Grounding and Bonding
Should have been
Proper Grounding and Bonding
I rearrange things so everything entered at a common location and everything was bonded together and all damage stopped.
Image from: page 3.19 fig 3.10 in the ARRL book on Grounding and Bonding for the Radio Amateur Copyright ARRL

7. What’s the difference between bonding and grounding?
Bonding is tying items to a common potential
Grounding is tying to earth potential (for this presentation)
Understanding the difference is important.
Image from ARRL book on Grounding and Bonding for the Radio Amateur, figure 1.1 Copyright ARRL

8. What is the cause of damage?
Is it voltage or current?
Yes
It is both, with current being the worst of the two
The reason is current develops a voltage across a resistance (impedance). For example 10 kA through a 1 Ohm resistance will have 10 kV across it.
V = L * (di/dt)  assuming a 0.15 mH inductor, 10,000 amps and 10 microseconds = 150,000 V
Al Torres: The Ldi/dt is very important because it only takes a tiny amount of inductance to generate a significant voltage. It you use 8 microseconds, the voltage will get worse for the same current. So parallel inductances are good.....to reduce the L.
Originally used 45 microseconds, changed to 10 microseconds

9. Resistance is ……. Resistance is both a friend and a enemy
In a way lightning protection breaks down to just Ohm’s law
However you have to consider inductance as well as just plain resistance, so it is impedance verse just resistance.
For example:
0.5 inch coax about 100 ft long is about 51 µH
A tower is probably about 5 µH per 10ft.
Tower Joint resistance is ohms

10. Soil Resistivity Comparison
Surface Soils ,000
Clay ,000
Sand and Gravel 5, ,000
Surface Limestone 10, ,000,000
Limestone ,000
Shale ,000
Sandstone 2, ,000
Granites, Basalts, etc 100,000
Decomposed Gneisses 5, ,000
Slates, etc 1, ,000
Soil Type Resistivity (ohm-cm)
From Bicse pdf Soil Resistivity and Grounding System Testing - Roy Whitten - Lyncole XIT Grounding

11. Typical Ground Performance Requirements
– National Electrical Code (NEC) < 25 OHMS
– IEEE Standard Equipment Dependent
– IEEE Standard < 5 OHMS
– Motorola Standard R < 10 OHMS
– Verizon Wireless < 5 OHMS
– Typical Telecom Switch < 2 OHMS
From Bicsi pdf Critical Facility Grounding - John Howard - Lyncole XIT Grounding

12. Ground Resistance Calculations
For example, if the soil resistivity is 50,000 ohm cm (mid case sand), the rod diameter is 1.73 cm ( inch), and the rod length is 243 cm (8 feet), the resistance-to-earth is ohms.
Consider 10 kA through ohms is 2,067,381 Volts at the top of the ground rod
So how many of you are excited about a single ground rod on your tower with a resistance of ohms?
Keep in mind wire inductance and resistance puts the bottom of the tower at higher values.
Keep in mind this is what the top of the ground rod will be at. The tower leg will be more as the wire to the ground rod will add in inductance.

13. Ground Resistance Calculations Page 2
If soil resistance is 5,000 ohm cm then resistance- to-earth is Ohms
If soil resistance is 2,500 ohm cm then resistance- to-earth is Ohms
If soil resistance is 100 ohm cm then resistance-to- earth is 0.41 Ohms
How excited are you with 1 ground rod at Ohms with 10 kA current puts the bottom of the tower 4,135 V?
Or three ground rods at 0.14 Ohms or 1,378 V?

14. Grounding Improvements
Improvements come in several forms. One can lengthen the rod, increase the diameter of the rod, add more rods, bond to structural steel or other buried metal, or use chemical rods. Chemical rods increase the conductivity of the soil around the rod, increasing its effective diameter.
ARRL book on Grounding and Bonding for the Radio Amateur Figures 4.4 and 6.6.
With 50 ground rods and 100 Ohm Soil, your ground rods would be close to 100 Volts
ARRL book on Grounding and Bonding for the Radio Amateur Figures 4.4 and 6.6 Copyright ARRL

15. Protectors and Misc.
Use coax protectors From Polyphaser, Nextek or Industrial Communications Engineers
If possible use quarterwave shorting stubs at VHF+
Use AC Line Surge protectors – use only Tripplite, SGL Waber or Polyphaser
Only use Safety Certified products IE UL, Nemko, CSA, ETL, etc.
Use a AC Line Surge protector in the service panel (installed by a licensed electrician)
Use only safety certified power supplies that have a CE mark, such as Samlex
Guy wires need to be grounded

16. Lightning According to IEEE
Typical Lightning strike is 8 s rise-time and 20 s fall-time
IEEE Lightning Strike based on Probabilities
Lightning is an electromagnetic pulse, no DC

17. Melting of Copper as Function of Current and Time

18. KP4AQI Steps for Selecting Grounding Conductor
Step 1: Select the level of protection; recommend 10% level strike at 65 kA for a 90% protection
Step 2: Select a conductor capable of handling 65 kA current for a transient of 8 s. This conductor should be 3 times the fusing current (see previous slide Table)
Step 3: Skin Effect for this pulse will be 2.18 mils at 1.5 MHz. Use 3x Skin Depth or 6.54 mils conductor surface depth
Step 4: Using conductors in parallel reduces ground conductor inductance. Two 12 AWG conductors will have lower inductance than a single conductor; if you twist the conductors, inductance drops further
Step 5: If you can afford a copper strap, then you are better of because they provide a larger surface area (Skin Effect); you can get parallel straps to reduce inductance

19. Typical Copper Straps

20. Things I do Drip coils or Drip Loops at key points to add impedance
Take coax off the tower below the connections to the ground rods with sharp corners (adds inductance)
Use quarter wave shorting stubs on single band VHF/UHF
Tripplite localized protection
Single point entry with bonding and grounding
Whole house surge protection
Ground all legs of tower, typically put a 4 ft ground rod on each tower leg before pouring concrete
Ground rods are at a slight angle to allow for less of a angle connecting to the rod (less than 45 degrees)
Run coax between two legs of the tower
Drip loops at the wrong place can make things worse.

21. Summary Single point of entry Bonding is a superb thing
Lots of ground rods
Minimize resistance and impedance to ground
Use heavy gauge or larger wires or copper straps
Ground every leg of the tower
Ground guy wires
Get out of the shack during storms
Think safety
This presentation only scratches the surface
Lightning is very complex

22. John Monteith, WB8YXD along with
Special Thanks to
H Ward Silver, N0AX for supplying the images for this presentation that are in his book
Dr Al. Torres, KP4AQI for his additional information
And
The reviewers:
John Monteith, WB8YXD along with
H Ward Silver, N0AX and
Dr. Al Torres, KP4AQI

23. You can email me at: WB8VSU@arrl.net jim@trc.guru (JB Consulting)
7/4/2019 1:10 AM
Questions?
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(JB Consulting)
Thanks for listening
JBRC Consulting LLC dba JB Consulting
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.