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Author Topic: Proper roof peak antenna grounding  (Read 4026 times)
N9LNM
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Posts: 1




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« on: April 13, 2013, 07:39:51 AM »

I’m putting up a new antenna and want to protect myself as best I can by properly grounding the whole setup.  I’ve read many of the forum posts here, but still don’t have a clear/complete solution.
 
I know enough to know I don’t know enough!
 
Can I protect my home and my home electrical systems, including my radio equipment, from a direct lightning hit to my antenna?  I don’t know of nor have I found a solution that guarantees that.
 
Can I protect my home and my home electrical systems, including my radio equipment, from lightning and/or static electricity near my antenna?  I think so, but is what I can do (see below) going to guarantee that?
 
Power line electrical surges I understand and think I have covered.
 
Ground wire for roof peak mounted tripod
·         2AWG Guage     2 AWG, seriously?
·         Solid                      Strand ok?
·         Bare                       Insulated ok?
·         Laid on the roof and draped over the side of the house or mounted on insulators across the roof and down the side of the house?   If mounted on insulators, what kind?
·         Where’s the proper place to attach the ground wire to the tripod; where the mast sits on the tripod, or at the base of the tripod?
 
Rotator with 3 wire power line
·         How do I prevent electricity from traveling down this line into my house?
·         Use ‘standoffs’ to secure the power line down the mast?
·         Use ‘standoffs’ to secure the coax to the mast?
 
Antenna coax
·         Coax from antenna to a grounded lightning arrestor and coax from the grounded lightning arrestor to the transceiver
·         Laid on the roof and draped over the side of the house or mounted on insulators across the roof and down the side of the house?   If mounted on insulators, what kind?
 
Grounding solution
·         What I can do is put an 8’ ground rod into the ground.  What I can’t do is put in the ground rod AND some kind of ground system that goes all the way around the house and ties into the utility company’s ground rod.  From what I can see of the utility’s ground rod – it ain’t much!
·         What I can do is mount a mounting plate to the ground rod and mount the antenna ground wire and the coax lightning arrestor to the mounting plate.
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N3QE
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« Reply #1 on: April 13, 2013, 07:58:37 AM »

"Entrance panel" and "single point grounding" are the magic words.
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KB4QAA
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« Reply #2 on: April 13, 2013, 08:38:26 AM »

http://www.k9sth.com/Page_2.html
Glen's view, page down for Grounding Articles

http://www.w8ji.com/ground_systems.htm
Tom's view

http://forums.qrz.com/forumdisplay.php?33-Antennas-Feedlines-Towers-amp-Rotors
Read the three topics pinned at top

There are no guarantees when it comes to lightning protection.  However radio stations, cell operators and commercial operators with well designed systems regularly survive direct hits without damage.   Most hams aren't willing to spend the money and effort for a bullet proof system.  Still it is possible to have a very good system for reasonable cost and effort.

Note that a lightning ground and an RF ground have different requirements.
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W5WSS
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« Reply #3 on: April 13, 2013, 08:38:57 AM »

Roof peak located at an end of the roof?  Run the proper size wire such as, yes a large conductor like #2 from the top of the pipe "not the bottom". For example, the nearest junction where the antenna base clamps onto the pipe or pole. If you can slide the antenna down slightly in order to leave the pole protruding above the antenna is the "Ideal".
Route the large conductor straight down to an minimal 8 ft length Copper clad Earthing rod and use a ground rod clamp. Weather proof all the connections.

This is for antenna lightning protection path to Earth "outside" you can daisy chain more ground rods every 5ft and use 4ft rods and en circle the home for really good lightning protection.

For your DC safety station ground do NOT connect the rig and equipment to the antenna lightning Earthing rod.
rather do connect the rig and equipment to the AC Electrical mains panel marked GND.

Keep the rig Safety Ground separate from the antenna lightning ground system.

In short separate the antenna earthing system from the Rig safety dc system.

Even though the large lightning stroke can rise the voltage gradient potential enough to impose a commonality relevant to the two individual systems the inductance is minimized by your contributing systems isolation relative through the soil mediums and distance apart.

73
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W5WSS
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« Reply #4 on: April 13, 2013, 08:50:26 AM »

As an addendum to my previous post one can also in addition to, install an in line coaxial center conductor antenna lightning protection device located near the antenna near the point at which the coaxial feedline connects to the antenna and bond the device to the junction where the large #2 leads down to that first earthing 8ft rod.
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KF7P
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« Reply #5 on: April 15, 2013, 04:11:08 PM »

It is possible to get good lightning protection in your situation, but if you aren't able to get in more than a single ground rod I'm not sure how confident I would be in stopping any/all damage via lightning.  But you need to start somewhere.  Some other ideas:  Run coax to the ground, don't shortcut it in at roof level.  Run the biggest wire you can afford from the antenna to the ground rod(s). You can use an arrestor that mounts on the ground rod like this http://www.kf7p.com/KF7P/GroundRodClamps.html or go with the XYL pleaser, http://www.kf7p.com/KF7P/EntrancePanels.html   There are also Morgan Mfg. units that will work for your rotator line.  Also check the tech page for lots of good info on grounding.



Chris
801-231-2658
www.KF7P.com
Custom tower and grounding accessories for amateur radio

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W5WSS
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« Reply #6 on: April 15, 2013, 07:34:18 PM »

Kf7p Hello I took a look at your products and like them.

I also agree completely with your suggestions, especially the lightning arrester down at the rod and then bringing the antenna feed line back up to the equipment.
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K1CJS
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« Reply #7 on: April 16, 2013, 03:46:16 AM »

Yes, it is possible to get lightning protection, but the odds are that if your home is hit direct you're going to suffer some damage.  Commercial sites that have lightning protection have massive protection schemes including either multiple ground points or a ground halo, and are made of materials that won't ignite and burn if hit by lightning.  Materials such as steel, aluminum, and other metals and or cinder block, brick or concrete.  You will NEVER see any sort of wooden structure in a commercial radio site with a tower.

The good news part of it is this:  You're more likely to hit the lottery than you are to sustain a direct lightning hit on your antennas or your home.
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W9GB
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« Reply #8 on: April 16, 2013, 06:06:25 AM »

Lightning protection systems should be installed by a competent person(s) with a full understanding of the lightning protections standards: LPI-175, NFPA780 and UL96A. These standards must be followed during the design, installation and inspection of a lightning protection system.
http://www.kuefler-lightning.com/general-notes.htm

You have electrical contractors in your area (Indianapolis, Carmel),
 that specialize in Lightning protection systems.
http://www.lightning.org/installers/?state=25&country=
« Last Edit: April 16, 2013, 06:16:31 AM by W9GB » Logged
KV7W
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Posts: 136




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« Reply #9 on: April 16, 2013, 07:15:38 AM »

I've installed a lot of grounding for commercial sites. Every engineer has an idea of what will work best; UFER, ground ring, individual leg grounding, static ball - I wasn't hired to question it, but to make it happen. (Although I did question one job where the engineer wanted me to run a massive ground wire from the tower, through a commercial office building to the electrical room for single point.)

All the different scenarios have about the same idea - make the current from ground look more conductive from outside near the tower than inside the building.

2AWG is common for lighting ground. You need that mass of copper running straight down from the tower to look more inviting to the lighting than your feed lines. The more you load your tower, the more #2 and ground rods you will need. If you ground your tower legs with #2 and ground your feed lines with #6 to a buss bar that goes to ground with #2 - the electrical safety ground for your various rigs is going to look pretty puny with the #12 wire, and that's good! Single antenna with one feed line for your roof? #2 might be overkill, but it's cheap insurance you only have to pay for once.

The construction material choices for tower shacks has more to do with potential ice than lighting. A 300 pound ice-sickle falling a few hundred feet has a lot of potential energy! I went to one site that had a 170' freestand with a cinder block shack. Lighting hit and exploded a 2" aluminum mast at the top. In the shack the arc flash traveled through a rack to the electrical conduit. From there it branched; one path blew an unused breaker box off the wall in the next building, another path traveled the underground phone line to the service connection an 1/8 mile away where it exploded, and a third - got into the cinder block rebar; traveled all the way around the building, cracked every wall with blowouts at the corners. One upside - most of the equipment was OK and nobody was there at the time. I went outside and couldn't find a ground system. They must have figured the J bolts were "good enough". About a dozen ungrounded feedlines went into the shack though. This was an old site. They must have been used to just fixing the minor lighting damage over the decades, until this time when they took a direct hit.

Another old tower I worked on had a wood shack. It had a single #6 wire from a leg to a ground rod connected by an acorn. Every couple years they had damage and I'd find that acorn loose. I just started checking the acorn in the summer and it was usually loose again - lighting hits probably loosened it up. Cadweld and ground kits for the feedlines fixed it.

I used to think lighting was magic the way it would arc flash through the air inside a shack and bypass racks and equipment to find some oddball nail in the wall more inviting. I now think it's not magic, but as simple as two resistors in parallel - less current will flow through the higher value resistor. From an operating point of view, we want good connections between our stations and the antenna. The better we make these connections, the better lighting ground we need. A lot of Ham's lives have probably been saved by their inability to solder a proper 259.

#2 isn't that bad to work with. Insulated and stranded is fine. Make a large radius for any bends, 12" or greater is nice, but try to make the radius bend of the ground wire greater that of any feedline. Check into making a feedline ground where it enters the house. It's not that involved and only expensive if you want to be.
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N1RND
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« Reply #10 on: April 16, 2013, 02:37:33 PM »

Roof peak located at an end of the roof?  Run the proper size wire such as, yes a large conductor like #2 from the top of the pipe "not the bottom". For example, the nearest junction where the antenna base clamps onto the pipe or pole. If you can slide the antenna down slightly in order to leave the pole protruding above the antenna is the "Ideal".
Route the large conductor straight down to an minimal 8 ft length Copper clad Earthing rod and use a ground rod clamp. Weather proof all the connections.

This is for antenna lightning protection path to Earth "outside" you can daisy chain more ground rods every 5ft and use 4ft rods and en circle the home for really good lightning protection.

For your DC safety station ground do NOT connect the rig and equipment to the antenna lightning Earthing rod.
rather do connect the rig and equipment to the AC Electrical mains panel marked GND.

Keep the rig Safety Ground separate from the antenna lightning ground system.

In short separate the antenna earthing system from the Rig safety dc system.

Even though the large lightning stroke can rise the voltage gradient potential enough to impose a commonality relevant to the two individual systems the inductance is minimized by your contributing systems isolation relative through the soil mediums and distance apart.

73
I always thought that all parts of a ground system are supposed to be bonded together, to keep every part at the same potential.
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KB8VUL
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Posts: 105




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« Reply #11 on: April 19, 2013, 06:23:45 PM »


[/quote]
I always thought that all parts of a ground system are supposed to be bonded together, to keep every part at the same potential.
[/quote]



They are.
Here's the story on grounding at a broadcast, commercial two-way cellular  prospective.
First thing to know, you are NOT trying to build a path for lightning to follow without damaging the path or the connected equipment.  That would be impossible as a direct hit is tens of thousands of amps.  The induced voltage across a piece of copper wire in the one aut size with a wire length of 50 foot is over ten thousand volts on a direct hit.  Copper has resistance, it's not a perfect conductor.  Due to the voltages and currents present in a direct strike, that resistance creates a voltage difference between one end of the wire and the other. 
What you are trying to accomplish with grounding is two fold. 
The first thing is common potential.  If the case of every radio connected to the grounding system peaks at 75KV the potential between the cases is still 0V.  If one radio case goes to 75KV and the one next to it remains at 1KV, you get a big bright light in the shack, followed be a visit from the guys in the big red trucks that tear stuff up and throw water on it. 

Second thing is floating potential.  Lightning prefers to hit things that are at a higher than ground potential.  But what does that mean?  Go find a ham that has a home brew long wire dipole with no balun in the center.  He will tell you about how when the storms are coming and the wind is blowing his antenna tuner will start arcing internally.  One side of that antenna is going to a higher than ground potential and the other side is not.  When the voltage rises to the point that the air insulator in the antenna tuner can no longer hold back the voltage, it arcs over.  Towers will do the same thing, as will antennas that are not DC grounded (meaning the radiating element is not connected to ground in any way).  The reason that lightning will hit things with a higher potential than ground is the voltage is raised, and it's now the path of least resistance. 
So you need to deal with that as well.  So how does it all come into play and work.

A grounding system has to be built.  Now a commercial radio tower has a pretty substantial grounding system.  It's refereed to as a halo ground.  A halo ground consists of a heavy copper wire ring around the perimeter of the site that has ground rods of various lengths thermally welded to it.  All halo connections are exothermic welds.  No split bolts, no solder (never solder a ground, the heat of the strike will vaporize the solder and render the connection useless at it's most important time).
Then heavy wire is welded to the tower legs and then welded to the halo.  After that, the fence is grounded in a similar manner.  This keeps the tower, fence and anything sticking out of the ground at the same potential.  There are additional wires welded to the halo that are connected to ground bars in the building and on the tower.  Every coax line as it comes off the tower or enters the structure has a grounding kit put on it that is connected to the exterior ground bar.  The line then enters the building and is terminated at a lighting arrestor (polyphaser).  The lightning arrestor is mounted to another ground bar that has a connection to the halo.  In addition every breaker panel, transfer switch and radio rack is tied to this ground bar. each rack has a separate ground bar that ties over to the master ground bar that the radio equipment grounds to.  The main power coming in goes through a lightning arrestor as well, and of course it's tied to the ground bar. 

There are specific wire gauges that are required by an installation standard known as R-56.  Every radio has to have a number 6 wire to it, there can be no more than 3 number 6 wires connected to a number 2 wire back to the ground bar.  radios must be physically grounded via a different path than the ground for the rack they are mounted in, but it must be grounded as well.  Any connection that is not welded with regards to wire ladders must be strapped by a number 6 wire.  All wires must be connected via compression type (crimped) lugs. The minimum bolt diameter for a lug is 1/4 inch.  Bolts must be brass.  The list goes on.  R-56 is like 700 pages.  If you google it you will find it and if you can't sleep start reading it, it will put you right to sleep. 

So back to ham radio.  Obviously a commercial tower grounding system costs as much as a small car.  So we obviously can't lay out that level of money to build a grounding system.  So how do we go about it.  First is getting a ground field built.  We aren't going the route of the halo, but we can still put in a good field.  Pick a spot and measure out an area that is 8 foot by 8 foot.  Go buy enough ground rods to create a grid with 2 by 2 foot spacing.  Dig the top foot off the 8 by 8 area and drive the rods in creating the grid.  Now you can tie the grid a couple of ways.  First is get more ground rods and weld them to the driven in rods so they are all connected.  Welding is done with CadWeld one-shots.  Remember that you are wanting all this below grade so drive the rods deep enough that you can cover it all up and not hit anything with the mower.  If the cadweld shots give you sticker shock, remember that you are trying to keep your house from burning down, if the sticker shock still exists, you can get a buddy with an acetylene torch to braze the connections together.  DO NOT SOLDER IT!!!! Now the grid is done, you need heavy wire (read that as 0/4) to connect it to the house.  Sticker shock again, 3/4 copper pipe will work if its flat, so get some pipe and a big hammer.  Remember that you can't solder any of this,,, brazing is the way to connect the sections.  As the line passes the tower, run a line over to it to be connected as well.  Don't cadweld a Rohn 25 or 45 tower, you will only burn holes in the tower.  remove the galvanize with a sander or grinder and braze it.  Be careful of the heat.  don't melt the tower leg.  Get a can of cold galvanize and paint once it's cold to protect to protect the metal.  Regular paint ain't gonna cut it.  Run the line into the house and over to the ground bar.  Ground bars aren't cheap either, but they are best, if you are a real tight wad, more flattened copper pipe is in order.  Run a number two wire to your operator position, run a number 2 wire to your breaker panel remember that you need crimped lugs. Drill a hole in the side of the panel, clean off the paint and bolt it down.  Put another ground bar at the operator position and connect all your stuff to it with 6 or 8 gauge wire.  Radios need 6 gauge.  Computers and the like will be fine with 8 gauge. These runs can be stranded or solid.  Mind you there isn't really a difference in stranded or solid wire of a specific gauge.  8 stranded is larger than 8 solid but can carry the same power. 

It's not a bad idea to ground everything else in the house as well if it's convenient.   Furnaces, water heaters, and such.  Install a panel rated surge suppressor in your breaker panel.  Install a phone line suppressor on the incoming phone line and ground it over to the grounding system.  Even the cable should be tied to it.  At that point, everything has some protection.  Now, don't think that you will never get hit after all this.  You can still be hit, it's just lowers your chances.  At the point that everything is the same potential as the ground outside, and nothing is floating, if lightning is looking for a path, you have effectively ducked and aren't standing there holding a sign saying come hit me.

If you have long wire or dipole antennas that are not DC grounded, either buy a grounding coax switch or connect a SO-239 connector (or whatever you have on the incoming coax) to the bar and connect the antenna to it when not in use. 
Speaking of coax, get coax suppressors and install them on a bar near the entry point of the lines.  If you want to go full boat, either buy grounding kits, or take number 8 wire, remove 2 inches of jacket from the coax coming down the tower and connect the wire to the outer braid with small hose clamps, then wrap the connection with weather proofing.  Connect the wires to the copper bus at the base of the tower with bolts and lugs.
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KB8VUL
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« Reply #12 on: April 19, 2013, 06:45:30 PM »

I should also point out that this is a potential ground and not an RF ground. 
I didn't go into AM broadcast tower grounding and the field under them because it typically will make you really feel inadequate.  AM broadcast stations have removed acres of top soil and laid down acres of special copper screen that all gets brazed together and then covered up.  The central point is always the tower and the size of the grid is related to the operating frequency.  It's basically a ground plane antenna for really low frequencies. 

If you are a glutton for punishment and want to install an RF ground, head out to the local farming materials dealer (Tractor Supply) and get some rolls of galvanized high tension fence wire.  The stuff is great for antennas to so keep that in mind.  From the location of your tower, or HF antenna feed point measure out wire lengths that would be 1/4 wave for all desired operating frequencies.  you want a minimum of 4 wires per frequency, but you can have more than 4.  Start cutting them into the ground with a shovel so they are below grade.  Run them in opposite directions for their cut frequency length.  Make sure when cutting to length that you leave a bit to get them connected all together. 
Once they are all in the ground, break out the copper pipe again and bend it in a circle.  Call the buddy with the torch back out and have him braze all the wires to the copper loop.  Also tie the loop to the potential ground system for safety via a large conductor (more flattened copper pipe).  you now have a poor mans RF ground connected to the system.  It will have a marked effect on HF communications.
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KV7W
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« Reply #13 on: April 20, 2013, 07:24:41 AM »

That's a pretty good description of a commercial ground system and it even gets worse when the fence is some distance from the tower. Looking at the problem from the commercial side - you spare no expense to keep a site operational. A tall tower will get hit by lighting and needs to be operational while being hit.

It seems like amateur operators have the cards stacked against us, but do we?  Ham antenna systems get hit by lighting, but is the solution to look at a commercial system? Even with all the copper you've described, you know as well as I do, sometimes it doesn't work. Arc flash can travel through air.

I wonder why more effort hasn't been put into developing ways to isolate the antenna system from the shack during lighting storms? I see a lot of ham's do the best they can to replicate a commercial system, but if they cut any corner lighting will find the weak link.

W5CYF posted a video of what a lighting strike does.

http://www.youtube.com/watch?v=suaMa1h8u2Q

He had disconnected his feedline from the antenna, but didn't think about the arc flash passing through the insulation of his coax from his rf ground. He was really lucky it was disconnected; even though the strike took out most of his household electronics - his house and shack were mostly secondary damage.

Now, would he have been safe if he would have had ground rods sunk at the antenna with another sunk at his service entrance w/#2 routed around the outside of his house to the electrical service ground and all his shack equipment buss bar'd to a ground grid? Good chance he would have been, but that leaves a chance he could have sustained damage anyway.

If he had disconnected his feedline at the service entrance of his house and tossed the coax about 6' into his yard, it might have had the same effect as a $3K ground system. If the antenna system is easily isolated from the shack, doesn't that take care of the problem?

I wish there was a way to disconnect multiple feedlines quickly. I know it doesn't take too much effort to take apart a PL, but it still takes effort. Be nice to walk into the shack and just flick a switch and hear a solid mechanical "thump" as the antenna system is connected to the shack. 

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K1CJS
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« Reply #14 on: April 20, 2013, 10:23:11 AM »

Yes, arc flash can and does travel through air.  That is why lightning rods were installed on high risk buildings--and still are.  The trick is to make the lightning rods more attractive to lightning strikes, which is to say make their impedance to a good ground system the least it can be.
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