Lightning Protection

[wqgj587]

Getting ready to set up my own tower. I know how to ground the tower itself.

For the first month or so, a temporary radio will be housed in a steel box mounted to the tower,, then the permanent one will be housed beside in small , very small shelter.

What more will need to be done as far as lightning control beside good copper grounding on the tower itself.

Any sort of inline coax grounding?

Thanks for any advise

Tom

[Jim202]

Not trying to tell you how to do, but I would suggest that you do a search on the internet and
look for a copy of the Motorola R56 standard. Not trying to be a supporter of any one company
over another, but that standard does have a good section on tower grounding and site grounding.

As for the coax, yes you should put some surge protection on it before the radio. The
effectiveness of your efforts will depend on just how good your "ground system" is. I use the
word system because no one thing will provide total protection. You need a good ground
"System" (more than one ground rod) for the tower, surge protection on the AC power being
used, surge protection on any telephone lines being used and on the coax cables being used.

The tower ground system is probably the most important effort you can put into the "system"
to protect your equipment. Ground rods use the resistance of the soil to provide the total
low resistance that your looking for. In doing this they rely on what many call the cone of
influence around them. If you place ground rods too close, the cone of influence will overlap
and not produce the lowest resistance you can obtain. Along these lines, the best spacing
then is to place the ground rods at least twice the distance of their length apart. In simple
terms, if your using 8 foot ground rods, you place them at least 16 feet apart. If your using
10 foot ground rods, you would space them 20 feet apart.

The grounding connections should all be made with exotheric welds. This provides the lowest
resistance connection and won't have and corrosion over time to reduce the low resistance
connection. Caution should be used on making the grounding connection to towers. You
don't want to just place bare copper wire on the galvanized tower legs. Over time, the
copper will react with the zinc and the zinc will be leached out of the galvanization on the
tower. Over time you will have rust taking hold and start to destroy the tower. If you
don't have a grounding plate on the tower, then the best second choice would be to use
a bronze grounding clamp to be the interface between the galvanized tower and the copper
wire. Many commercial radio carriers have used plated wire to reduce this problem. They have
also standardized on using # 2 solid copper to reduce oxidization of the ground wire itself.

Hope this provides you with some guidance in your efforts.

Jim

Getting ready to set up my own tower. I know how to ground the tower itself.

For the first month or so, a temporary radio will be housed in a steel box mounted to the tower,, then the permanent one will be housed beside in small , very small shelter.

What more will need to be done as far as lightning control beside good copper grounding on the tower itself.

Any sort of inline coax grounding?

Thanks for any advise

Tom

[motorola_otaku]

And guess what, R56 is a free download now.

http://motorola.wirelessbroadbandsuppor ... 7bbba93fad

The chapters regarding site grounding will be of interest you.

[motorolo]

A few years back, one of the engineers over at PolyPhaser wrote a series of articles on lightning protection for QST. The articles have a wealth of information, and were written to be accessible for any skill level. Definitely worth checking out, in addition to what has already been posted in this thread.

http://www.arrl.org/lightning-protection

The articles I'm referring to are the topmost links on that page, although there is other good information available below it, too.

[Jim202]

If your asking questions, then the best bet is to follow all the suggested information here and the other sites
that have been suggested. Being in the field for well over 45 years now, I am always still learning about it.

You have a ways to go to fully understand the reasons for doing the different steps. Like many that have
got their first ham license, read the book and memorize the answers. The understanding will come with
time and doing it. Lightning has no friends. Just enemies.

[desperado]

I was reading some information on lightning and EMP protection the other day and found that people are going much deeper with grounding rods than previously.
New builds are drilling grounding wells and putting rods in 60 or better feet deep.

There are also findings that R56 (I live by it too) doesn't take into account for the currents from a direct strike, and the voltage induced across the number 2 ground wires when the are long.
Point is that you can't have too much grounding, but you can easily have improper grounding.

Without going into all of it here are some high points to consider.
First is ground EVERYTHING to the same point. This means your electrical, tower, equipment, water pipes if metal and any structural steel in the facility. If it's metal and it can bring in lightning, ground it.

Make your ground buss runs as heavy as possible. Minimum is number 2 wire. Bigger is better. R56 standard says that a number 6 ground can have no more than 3 number 6 connections on it.
This is important. Also, keep grounds short as possible. Due to the current involved with lightning being in the thousands of amps, wire with milliohms of resistance per foot will still have a significant voltage induced on it, the shorter the wire, the less resistance it has for the run.

Do NOT ever solder any ground connections. Crimp lugs on with proper crimping tools, not a hammer or vice grips.


Use good brand name lightning arrestors not the cheap stuff. A fried MTR 2000 or Quantar with lightning damage is much more expensive to repair than the $20 you save on the cheap arrestor. That goes for ground wire too, the heavy stuff ain't cheap, but it's WAY cheaper than a repeater.

[Jim202]

To follow on what "deserado" has said, you can't have too much.

I will give a prime example. The company I use to work for in Louisiana, just north of Lake Ponchartrain, had 2
each, 500 foot towers about 20 feet apart. The site was used for paging and cellular. R56 was enforced there
in both the underground and inside the shelters.

The site would take a direct hit about once every couple of weeks. It would cause some damage to the
telephone interfaces for the paging equipment. My boss asked to have me go out there and try to find the
cause of the problem. We took a backhoe and dug up the ground to expose the ground system around the
towers and the shelters. Everything was done right. All the connections were exothermically welded to
the ground rods, tower and equipment shelter ground bars.

Went home that night and thought about it. In the morning, I made the suggestion that we dig a couple of
trenches out away from the tower and bury a string of ground rods the length of the trenches. Put in additional
ground rods every 16 feet (was using 8 foot ground rods) apart. Welded the #2 solid wire to the ground rods
and tied it back into the existing grounding system.

Filled in the trenches and sat back and waited. Waited some more and had a number of bad storms go through.
Best we could figure, was that even though we had a high ground water, clay soil, it just couldn't dissipate
the direct hits the towers were taking. The fuses in series with the telephone lines were saving the equipment
before the additional ground radials were added. You could take a shovel and dig down 6 inches and get water.

The moral of the story here is to make sure you have a low resistance, low inductance ground system that
can dissipate a heavy hit. In some soils, that may mean pushing longer ground rods into the soil. If the
ground system can't get rid of the high current, it is going to go someplace and cause some sort of damage.
I have seen some ground rods that we pulled after testing them, that had the soil melted to them into a
glass type glob around the rods. This is a sure indication that the ground system has failed. Bet you also
are having major equipment damage at a site like this.

It may seem like a real pain in the lower extremity to do a good soil resistance testing of your ground system.
But you need to do it once in a while. You also need the proper test equipment to do a complete test of the
ground system. You can't just hook up a low resistance meg unit and call it good. You actually need dig
down to each ground rod and use a clamp on meter to get below the welded wire connection. Normally
this type of testing will only take place after you start seeing a pattern of equipment damage from multiple
storms. It takes time and plenty of man hours to do it correctly. Then you have to figure out where the
problem is after all the testing. Don't forget that you have to lift the power company ground and neutral
while doing this testing. Generally you end up shutting down the site for a couple of days.

Jim


Jim

[Bill_G]

I have some really neato matching base station cabinets with bulged out sides. A little paint, and a doily - perfect end tables. You might be able to put a keg in them now with a tap out the side. The possibilities are endless.

[desperado]

R56 standard says that a number 6 ground can have no more than 3 number 6 connections on it.
.

This was stated wrong.
A number 2 wire can have no more than 3 number 6 grounds branching of it.

[Astro Spectra]

While there are all types of gas tube protection devices on the market it is hard to go past two 1/4 wave long shorted coax stubs spaced a 1/4 wave apart on your antenna feeder.

You can build easily this out of two N type T pieces. When you make up the stubs leave plenty of coax inner exposed after the short and use that to connect to your station ground.

If you use decent crimp connectors and tools it’s about 30 minutes work using RG-213. You could also make then from Heliax if you're keen.