grounding rooftop discone

[COM19pr]

recently put up a Jetstream JTD2 discone antenna on my roof for sdr. i used a metal non-penetrating roof mount system, and that sits on a thick rubber mat.

i connected a #30 gauge ground wire to the base and ran it alongside the coax antenna cable with tiewraps to the ground. there it branches off to a copper rod into the ground.

will running the ground wire next to the antenna coax cause any issues or should they be separated a bit?

 

[mmckenna]

30 gauge? That's exceedingly small. Are you sure it was 30?

Running the ground wire along next to the coax shouldn't be a problem for the reception, however you should be running a lightning ground as straight as possible down to the ground rod with no sharp bends. I believe NEC require #6 (6 gauge) or larger.

 

[dlwtrunked]

recently put up a Jetstream JTD2 discone antenna on my roof for sdr. i used a metal non-penetrating roof mount system, and that sits on a thick rubber mat.

i connected a #30 gauge ground wire to the base and ran it alongside the coax antenna cable with tiewraps to the ground. there it branches off to a copper rod into the ground.

will running the ground wire next to the antenna coax cause any issues or should they be separated a bit?

#30 (30 AWG) wire is only about 0.01 inch diameter. The larger the gauge number, the smaller the wire. 22 AWG is a common gauge for hook up wire . #6 (or 6 AWG) is about 0.162 in or about 1/6 inch in diameter. You are certainly not using #30.
American wire gauge - Wikipedia
30 AWG looks like this:
https://www.amazon.com/uxcell-Coate...nements=p_n_feature_two_browse-bin:6426179011

 

[prcguy]

The National Electrical Code for the US states a minimum of 10AWG copper wire for grounding an antenna and if you install an additional ground rod they require you to bond that to your house main electrical panel ground with no less than 6AWG copper wire. For more info see NEC article 810 which deals specifically with antenna grounding.

 

[Lauri-CoyoteFrostbite]

I think you meant some other value for the wire size than #30, COM19... (an aside, #30 copper wire has a resistance of something like 1 Ohm per 10 feet- the stuff of fusible links )

But its the placement of the ground wire that struck me. Running as you described it, COM, will be Okay to bleed off light static charges, but anything big, sudden and flashy is going to take the fastest, shortest rounte to the earth; likely thru your roof. That circuitously routed ground wire is going to act more like a big reactance impedence lump (yes, lightning behaves like RF- ) Lightning will ignore it, finding its way to neutral thru the path of least resistance (likely your house wiring, plumbing- metal siding............)

Once upon a time, I got a dramatic, first hand experience with the awesome brute strength of lightning. I was a guest at a high altitude meteorological research station- a station that pokes its nose up tauntingly at Zesus; its high on a mountain top famous for severe weather... ie: lots of lightning.

One of the first things I noticed about this station was the 60 foot tall steel "air terminal"- a cute phrase for a lightning rod- standing about 10 feet from the main building (living quarters, kitchen, instrument room- its not a big building.)
This "air thingy" was no slouch of a lightning rod- the base was 12 inches in diameter- tapering up to 3 or so inches at the top. Several coronal discharge rings festooned its length-- but what really caught my eye were the fuses fixed to the side of the behemoth. They were fusible link fuses commonly used in cars- these were in series, running parallel, with wire leads about 4 inches on either side, attached to large bolts weld'd to the mast.

Can everyone picture these?.. a slight current secondary path thru a fuse that bypassed the main, humongous steel lightning rod by some 8 inches. There were several of these "fuse bypass's"- each with different value'd fuses (5, 10, 20, 30 ! amps.) Imagine the total current thru the mast, if enuff current gets shunted off thru those fuses to blow a 30 amp'r.

Before my visit was over, I got a first row seat performance of the wrath of the gods... an electrical storm par excellence. Everyone in the station sat individually perched on tall wooden stools with ceramic power pole insulators on the stool legs, all this as Zesus hurtled bolt after bolt down at us. When they hit the "air terminal' the whole mast rung like a bell for several seconds. Coronas danced on the outside metal of the building's frame work- no one thought to leave the safety (??) of their stools while the fireworks blaz'd.

Enuff of the colourful imagery-

....When the storm passed, I went outside and looked at those fuses. Every one of them was 'blown !"
One of the researchers said-

"Humpf, maybe we should try higher value fuses next time"
.
Okay Guys- calculate the total current of a lightning bolt that could blow one of those 30 amp fuses while 99.99999% of the rest courses to ground thru the huge metal mast.

Think a piece of #6 wire is going to save anything, even with a puny secondary strike ?

But Hey !, run those wires for static discharges, read all you can about lightning- take a trip to look at a mountain top tele-comm site and see what the pro's do.

And don't taunt the gods

Lauri

 

[COM19pr]

30 gauge? That's exceedingly small. Are you sure it was 30?

Running the ground wire along next to the coax shouldn't be a problem for the reception, however you should be running a lightning ground as straight as possible down to the ground rod with no sharp bends. I believe NEC require #6 (6 gauge) or larger.

you're correct. my mistake. i should have written #10 gauge, 30ft. there is one 90 deg bend where roof meets house side then straight down to rod.

 

[COM19pr]

#30 (30 AWG) wire is only about 0.01 inch diameter. The larger the gauge number, the smaller the wire. 22 AWG is a common gauge for hook up wire . #6 (or 6 AWG) is about 0.162 in or about 1/6 inch in diameter. You are certainly not using #30.
American wire gauge - Wikipedia
30 AWG looks like this:
https://www.amazon.com/uxcell-Coated-Plated-Copper-Wrapping/dp/B008AGUC36/ref=sr_1_8/142-2266228-4822332?s=lamps-light&ie=UTF8&qid=1546365885&sr=1-8&refinements=p_n_feature_two_browse-bin:6426179011

thx for reply/linkks. i made a typo. it is #10 gauge and i bought 30ft of it

 

[COM19pr]

@Lauri-Coyote , the value should have read #10 gauge. i had purchased 30ft. interesting read you wrote, appreciate it. there are a few mountain top antenna farms around the valley here i could go check one out. it'll add to my education as i'm new to this and still studying for ham.
the house central a/c sits on the roof too so if Zeus misses aim just a bit i guess that a/c is toast. ;-) thx

 

[COM19pr]

it is 10AWG copper. i made a typo. the rod i rod i hammered into the ground is probably ~50ft from house main panel. this now is getting a bit above my current pay grade. i'll look at the NEC article 810. maybe call an electrician or pro-antenna installer to take a look.

thanks for the education

 

[prcguy]

BTW, 10AWG wire is specified by NEC but the level of grounding being discussed will in no way protect you from a direct lightning hit. Consider it impossible for you protect your equipment against a direct hit unless you rebuild your entire house electrical system from the ground up by a professional specializing in lightning protection. At the very least you should meet code specs even though its not designed for direct hits.

 

[Lauri-CoyoteFrostbite]

Hey COM

You might find this interesting

http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

This is my "go to" brochure for all things introduction Lightning.
.

Lauri

 

[COM19pr]

well, as far as that goes, then a direct hit on my home or neighbor's is left to my insurance policy. as you say, it it impossible to fully protect especially considering my limited resources. mr. & ms. lightning is going to travel where they darn well please through any possible path to my home on their merry way to ground.

i'm glad you brought this phase of it up though. i will get a pro to stop by and check it out to make sure it is up to elec code for my place so my insurance is being met.

 

[COM19pr]

Hey COM

You might find this interesting

http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

This is my "go to" brochure for all things introduction Lightning.
.

Lauri

i do find that interesting and downloaded the pdf into my ham/study folder. i'm sure i will revisit it many times. thanks much!

edit: Berkeley, huh? used to work at a place on University Ave multi-moons ago. can stll smell the coffee from au coquelet on way to office. thx all for your help!

 

[Lauri-CoyoteFrostbite]

I hope all this discussion about lightning has not unduly alarmed you COM...
The chances of a direct hit are very low for the average homeowner. The vast majority of the damages are caused by indirect spikes- surges that come in via power, data lines etc. As has been said, there isn't much you can do if a 'big one' has your name on it- but plenty that can be done about those nasty secondary spikes.

In my career I have seen a lot of lightning up close and personal - like that weather station story- or its effects when places have been struck. Even the most carefully engineer'd facilities aren't immune to its often whimsical nature- Like why after a direct strike on a remote site that blasted a 6 inch hole thru the side of a cinderblock building- did the only electrical damage that resulted was a single blown out light switch?
Chances are you will never experience any of these things.... but do take all the precautions in those booklets.

Years ago I pick'd up this pearl from a colleague-

"Trust in Allah, but hobble your camel"


Lauri

.

 

[AK_SAR]

Years ago I pick'd up this pearl from a colleague-

"Trust in Allah, but hobble your camel"

Lauri

As an old Gunny Sergeant once said:
"If a bullet has your name on it, don't worry about it because there's nothing you can do about it. It's all those other bullets addressed 'To Whom It May Concern' that you need to try to dodge!"

 

[COM19pr]

I hope all this discussion about lightning has not unduly alarmed you COM...
The chances of a direct hit are very low for the average homeowner. The vast majority of the damages are caused by indirect spikes- surges that come in via power, data lines etc. As has been said, there isn't much you can do if a 'big one' has your name on it- but plenty that can be done about those nasty secondary spikes.

In my career I have seen a lot of lightning up close and personal - like that weather station story- or its effects when places have been struck. Even the most carefully engineer'd facilities aren't immune to its often whimsical nature- Like why after a direct strike on a remote site that blasted a 6 inch hole thru the side of a cinderblock building- did the only electrical damage that resulted was a single blown out light switch?
Chances are you will never experience any of these things.... but do take all the precautions in those booklets.

Years ago I pick'd up this pearl from a colleague-

"Trust in Allah, but hobble your camel"


Lauri

.

points taken. no, not unduly alarmed. just want to be safe up to a point then hobble my camel as you say. adding to my education via the booklets.

 

[COM19pr]

As an old Gunny Sergeant once said:
"If a bullet has your name on it, don't worry about it because there's nothing you can do about it. It's all those other bullets addressed 'To Whom It May Concern' that you need to try to dodge!"

hear that in the Navy too.

 

[spongella]

I live dangerously, no ground wire on the discone. Hopefully the church on the corner's steeple will fend off strikes. Best is to always disconnect your antenna during the summer.

 

[jim202]

Having been in the cellular industry for many years and also public safety radio systems, lightning protection is one of the major concerns. Yes you can protect a tower site to survive a direct strike and still have the equipment stay operational.

I have was at one tower during a heavy rain and lightning activity. I was sitting in my vehicle waiting for the rain to die down when there was this very loud bang. The ground shook a little and I looked at the tower. It was steaming in the rain from the heavy current that went through the legs to the grounding system. The tower legs were about 3 inches in diameter. So you know it took some high current to make them hot enough to cause steam in the rain.

When the rain stopped, I got out and went into the equipment shelter. Everything was still functioning like it should. So yes, you can protect your tower and have it survive a direct strike. But it takes some careful grounding. It also takes the addition of surge protectors on cables coming into the shelter or building and you need to ground all the equipment racks together and tie them back to the common site grounding buss. Each coax cable coming into the shelter has the shield grounded. Plus there is a surge protector in series with the coax cable before it goes to any radio equipment.

You will read postings on different chat groups about how you can't survive a direct lightning strike. But that is an old tail that just keeps on showing up every time someone asks a question about ground their antenna system and radio equipment.

A good place to go to read about grounding and surge protection is to find a copy of Motorola's R56 standard. It is the bible source for most radio and cellular installations. If you search hard enough, you can find it on the internet for downloading. You might not find the current version, but just about any version will provide all the information to show you what should be done.

Roof top installations are much harder to ground. If your in a commercial building, the building steel is the best place to tie your grounds into. But in some cases, that building steel may not be a good ground. I have taken a ground resistance tester to see if the building steel ground is good for a low resistance ground. In some cases yes and others no. You don't know until you test it. If your in a tall multi story building, you have no choice but to use the building steel. If you in say a 3 or 4 story building and the building steel is not a good ground, then you have the option of running multiple ground wires from the roof to a ground ring in the earth around the building. I have had to do this at one building where we put an antenna mast on the roof for a cellular installation.

Just bear in mind that each location and antenna installation is different. It takes some time to figure out what your best choice of action is. There are a number of guides to go by. The NEC (National Electrical Code) is a good place to go to to see what your required to do. The section in it has already been mentioned in this thread by another person. If it's your personal home, then you need to check with your insurance company about what they have for requirements. They are the ones that will have to come out for an inspection after a strike. If they fine an incorrect installation, they might give you push back on paying for any damages.

Hope this provides some information for those that are concerned about lightning protection. Oh one more item that I almost forgot to mention. The ground rod that is under your electrical power meter is very important to the surge protection you might add to equipment in your house. These surge protection devices require a good low resistance ground. This is provided by the neutral wire and ground wire in the wiring of the house. It's good ground comes from that single ground rod under the meter. My point in bringing this up is I have had a lightning strike at one house I was in a number of years back. It took out out TV, several telephones, an electric organ, my sons fire pager in the charger and cracked the cable pre stressed slab of the house.

In investigation what caused the damage, I did a ground resistance test of the house ground rod. I had to kill the main breaker of the house electrical feed. Then disconnect the ground wire going to the electric meter. At this point you can now pull the ground wire off the ground rod. I measured the resistance and found it to be like 200 ohms. It should be like 5 ohms or less. So I pulled it out and replaced it with a new ground rod in a spot slightly different from the original one. Then I added a second ground rod 16 feet away from the one under the meter. Measured the resistance of my new ground rods and found it to be about 3 ohms. Inspecting the original ground rod, I found that it was badly corroded and as such could not provide a good low resistance ground. My suggestion is to look at how old the ground rod is and use the time of about ten years. If it's older than that, the ground rod probably needs replacing.

The reason to space out the ground rods the 16 feet apart distance is due to the "cone of influence" around the ground rods. It will extend the radius distance equal half the length of the ground rod. So if you use an 8 foot ground rod, the second one should be 16 feet away. If you use a 10 foot ground rod, the second rod should be 20 feet away. Placing the ground rods closer, the cone of influence will overlap and you will not get the full benefit of each ground rod. In other words, your wasting your money by placing them closer.

I know I have got long winded, but ground information is something that most people know little about. They also generally don't have a clue where to look to get information on it. So hope the information I have provided has opened up the eyes of some that may be concerned.

 

[prcguy]

Yes you can survive a direct hit and not have any damaged equipment, but its completely impractical and well beyond anything you can do at home. For starters you would have to rip out all existing AC power entry, wiring and antenna feeds, install a buried ground ring around the house and have everything installed again and tested and certified by someone with knowledge on the subject.

Cell phone sites and their lightning proof grounding have been engineered a long time ago and they are usually built in cookie cutter fashion with contractors simply following existing proven instructions on what to install and how to do it. A residence is vastly different with layers of problems to overcome and would require an expensive engineering session just to start the process. How much would it cost to completely rebuild a house electrical system, antennas and radio area to R56 standard?

For starters, the standard ground cable used for buried ground rings and all connections to ground rods is bare copper 500MCM at a cost of around $7 per foot and even a small house would need a couple hundred feet of that plus a dozen or more 10ft ground rods. Then there is trenching to bury that ground ring about 4ft below the surface all around the house and tower. Then there would be dozens of cadweld connections for all the underground cable connections. Then single point ground for AC power and antennas, which may not be practical for the home owner needing short runs of coax on the other side of the house and running them to the central ground point would add 100ft more coax to his radio room. And the list of problems and the price keeps growing.

After the engineering is done how many home owners would be able to perform all the work themselves to save $$ vs paying professionals to trench, install, rewire, etc? So what would it cost to lightning proof a ham or scanner room inside an existing house and all its antennas? My guess $50k range, could be less, maybe a lot more. Anything less than a completely engineered, professionally installed, tested and certified lightning ground system is simply false hope in a lightning strike.

I've worked for many years in the big satellite antenna and repeater site business and have been project engineer and lead engineer on many installs of antennas and their ground systems. I've seen the prices and bills from vendors and contractors and its way beyond what I could ever afford to lightning proof my own house. I know thousands of people, many who are hard core radio geeks like me and I have never met anyone who has been able to lightning proof their house. Its just not practical or affordable. So my standard advise is to ground to NEC standards and disconnect everything if lightning is possible including getting and feedlines connected to antennas well away from the house.

Having been in the cellular industry for many years and also public safety radio systems, lightning protection is one of the major concerns. Yes you can protect a tower site to survive a direct strike and still have the equipment stay operational.

I have was at one tower during a heavy rain and lightning activity. I was sitting in my vehicle waiting for the rain to die down when there was this very loud bang. The ground shook a little and I looked at the tower. It was steaming in the rain from the heavy current that went through the legs to the grounding system. The tower legs were about 3 inches in diameter. So you know it took some high current to make them hot enough to cause steam in the rain.

When the rain stopped, I got out and went into the equipment shelter. Everything was still functioning like it should. So yes, you can protect your tower and have it survive a direct strike. But it takes some careful grounding. It also takes the addition of surge protectors on cables coming into the shelter or building and you need to ground all the equipment racks together and tie them back to the common site grounding buss. Each coax cable coming into the shelter has the shield grounded. Plus there is a surge protector in series with the coax cable before it goes to any radio equipment.

You will read postings on different chat groups about how you can't survive a direct lightning strike. But that is an old tail that just keeps on showing up every time someone asks a question about ground their antenna system and radio equipment.

A good place to go to read about grounding and surge protection is to find a copy of Motorola's R56 standard. It is the bible source for most radio and cellular installations. If you search hard enough, you can find it on the internet for downloading. You might not find the current version, but just about any version will provide all the information to show you what should be done.

Roof top installations are much harder to ground. If your in a commercial building, the building steel is the best place to tie your grounds into. But in some cases, that building steel may not be a good ground. I have taken a ground resistance tester to see if the building steel ground is good for a low resistance ground. In some cases yes and others no. You don't know until you test it. If your in a tall multi story building, you have no choice but to use the building steel. If you in say a 3 or 4 story building and the building steel is not a good ground, then you have the option of running multiple ground wires from the roof to a ground ring in the earth around the building. I have had to do this at one building where we put an antenna mast on the roof for a cellular installation.

Just bear in mind that each location and antenna installation is different. It takes some time to figure out what your best choice of action is. There are a number of guides to go by. The NEC (National Electrical Code) is a good place to go to to see what your required to do. The section in it has already been mentioned in this thread by another person. If it's your personal home, then you need to check with your insurance company about what they have for requirements. They are the ones that will have to come out for an inspection after a strike. If they fine an incorrect installation, they might give you push back on paying for any damages.

Hope this provides some information for those that are concerned about lightning protection. Oh one more item that I almost forgot to mention. The ground rod that is under your electrical power meter is very important to the surge protection you might add to equipment in your house. These surge protection devices require a good low resistance ground. This is provided by the neutral wire and ground wire in the wiring of the house. It's good ground comes from that single ground rod under the meter. My point in bringing this up is I have had a lightning strike at one house I was in a number of years back. It took out out TV, several telephones, an electric organ, my sons fire pager in the charger and cracked the cable pre stressed slab of the house.

In investigation what caused the damage, I did a ground resistance test of the house ground rod. I had to kill the main breaker of the house electrical feed. Then disconnect the ground wire going to the electric meter. At this point you can now pull the ground wire off the ground rod. I measured the resistance and found it to be like 200 ohms. It should be like 5 ohms or less. So I pulled it out and replaced it with a new ground rod in a spot slightly different from the original one. Then I added a second ground rod 16 feet away from the one under the meter. Measured the resistance of my new ground rods and found it to be about 3 ohms. Inspecting the original ground rod, I found that it was badly corroded and as such could not provide a good low resistance ground. My suggestion is to look at how old the ground rod is and use the time of about ten years. If it's older than that, the ground rod probably needs replacing.

The reason to space out the ground rods the 16 feet apart distance is due to the "cone of influence" around the ground rods. It will extend the radius distance equal half the length of the ground rod. So if you use an 8 foot ground rod, the second one should be 16 feet away. If you use a 10 foot ground rod, the second rod should be 20 feet away. Placing the ground rods closer, the cone of influence will overlap and you will not get the full benefit of each ground rod. In other words, your wasting your money by placing them closer.

I know I have got long winded, but ground information is something that most people know little about. They also generally don't have a clue where to look to get information on it. So hope the information I have provided has opened up the eyes of some that may be concerned.