Grounding an Antenna....

dkreichen1968

Moderator
Staff member
#41
NEC does not require that attic antennas be grounded. Grounding may help prevent signal loss due to the fact that it completes the faraday cage effect for the coax cable. But, attic mounts are safe from lightning.
 

krisbee

DTVUSA Jr. Member
#42
I am a ham radio operator, and I have read a lot on grounding and antennas, and I have my setup heavily grounded with 8 ground rods, a radial system, blocks, etc., so I will try to keep it simple and not give bad info (some of this is reiteration of what was already posted):

1. You want all grounds to be at the same potential - the one serving the house and the one serving the antenna - this means they need to be connected together (bonded), and best done outside.

2. You can get zapped or your electronics zapped by lightning just near by (miles even). Enough voltage can be induced in your wiring to cause a discharge. I have been shocked on my electric fence once after I pulled the plug but touched the wire during a flash. The voltage came from the lightning two miles away induced in the fence wire! So it isn't just a direct hit you are working with - and the nonsense that your tree is bigger and will be hit first is crazy! Induced voltage (EMP) is more of an issue frying your electronics, and that doesn't need a direct hit to be trouble for you.

3. You want to get the voltage to ground outside, not through your equipment or in your house. A good grounding block should be ideally outside, and directly below the mast, Drive a ground rod there. Connect this rod back to the service ground of the house using thick (#6 or #8 solid copper) wire. Wire can be buried. Connect another grounding block before the entrance to the house and ground there as well. What you are doing is trying to direct the lightning/voltage to disappate where you want, not where it wants. If it hit the antenna, it will likely go straight to ground there, if it is induced, the long cable run is now the pickup of the voltage which is why you want to ground it directly outside before it comes in your house.

It isn't the easiest topic, and there are consequences for getting it wrong - But a good system doesn't have to be expensive, but it does have to be installed correctly. I have seen profesionals run their grounds with nice bends and turns. Lightning doesn't zig-zag, it usually goes fairly straight. Good ground wiring is rarely pretty!

The other major thing is having the grounds bonded together. If you don't, the path of least resistance maybe through your house and wiring! When everything rises and falls together, the strike's path of least resistance to ground is outside - where you want it! If your entrance is all the way on the other side of the house, most professionals will tell you to run a cable all the way to the other side of the house - some even will say put a ground rod every 16' along the way.

There is more to it, of course, but these three principles will help most people still reading this thread.
 

n2rj

Moderator
Staff member
#43
Hi Krisbee!

I'm also a ham (N2RJ). I do agree with everything you said. With regard to bonding grounds together, it is best to use an exothermic welding process such as Cadwelding. Otherwise you'll have to tighten clamps every year as they become loose.

The 16' rule for ground rods applies to 8' rods because the rods have an effective coverage radius of twice the depth they are placed in the ground. Placing them further apart will cause a potential difference. Placing them closer together won't hurt but is a waste, and copper is expensive these days.

I was actually working on a master grounding article which I should get back on. It's based on the Motorola R56 spec used by commercial radio installations.
 

Egor

DTVUSA Rookie
#44
YES, grounding IS VERY important, unless your willing to burn your house down that is.
Ground protectors come in two main varieties. Spark gap (The cable company thinks these are ok, but theyre cheap, and largely ineffective after just one nearby strike.
Next is gas-discharge type arresters, (which is a misnomer, as NOTHING on Gods green earth can 'arrest" a direct strike, you can only mitigate the damage).
These will cost you more, but they're effective for multiple strikes, over a much longer time. Don't forget a good ground rod. Lightning always takes the shortest path, and a 10' or longer ground rod will conduct a strike directly to earth if its installed close to the arrester. Otherwise, the strike will follow the path to your pricy TV, back out the power cable, to the ground in the power distribution wiring of your house,possibly starting a fire anywhere in the path. Lets NOT make Thor angry!
 

SWHouston

Moderator
Staff member
#45
Beyond using the proper components, it's equally as important that they be installed properly.
Many don't realize when you install a Ground Wire, and attach/run it near/on the materials of your house, that the proximity can cause a Fire.
It's better to ground a Mast as close to the Base as possible, but, IF you have to attach the Ground Wire to a structure, one can use Electrical Conduit to protect the Conductor.
It's important to remember, that when using Conduit as a Insulator, that it should "float" in the circuit, and the way to achieve that, is buy a Solid Conductor (appropriate gage) which has a Jacket.
.

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krisbee

DTVUSA Jr. Member
#46
And the lightning arrester is the least important part of lightning protection... sometimes it isn't even used. The most important thing is grounding properly, with proper materials and bonding all to a single point. A little 22g wire coming from a clamp to a ground rod isn't going to do it. 8ga solid copper wire, minimum, though flat wide copper ribbon/strap is better. Not sharp turns; lightning prefers gentle arcs. If you got a direct strike, you think that dinky bit of foam is going to contain that energy? It will find the shield and then go to ground. For induced strikes, which are much, much more likely, the shield should protect and dissipate the energy if connected correctly.

But never forget that your antenna ground should be connected to your house ground so everything rises and falls at the same potential. That is why dropping the coax near your house ground is ideal, nearby is okay but you will have to bury a ground wire connecting your mast ground to your house ground. And if it is on the other side of the house, you will have a lot of wire to bury, not to mention you should put another ground rod every 16 ft until you get to the service ground.

Also, another grounding block and grounded before it enters the house. You want all that fury outside, so always ground before it comes in. This is why, ideally you combine all of those functions with the service ground. If that is the case, however, I would add a few more ground rods to the service ground (again, spaced 16 ft from each other) to help dissipate any big charges.

All of that will be the most important part. The gas or spark tube is helpful, but more to make you feel better if you have done all of that. And at $15-$20, why not sleep better :)
 

FOX TV

Contributor
#47
You don't have to have a direct strike to lose equipment. The static buildup from a near by strike can kill RF front ends very easily since most of them are now Integrated circuits instead of discreet components. Grounding is not an exact science since we only know how high voltage acts in theory, but one cannot over do grounding at all. Discharge units may not even completely protect your equipment, but they may stop your house from burning down due to a direct strike. The best protection is to simply UNHOOK everything that leads to the outside world by using RF quick disconnects. I use them on my antennas and my DirecTV dish. I have DSL and I unhook the modem from power and from the phone line. I disconnect all RF cables and unhook everything electrical through one power strip. This is the only 100% sure way to protect your equipment. If you are not using it, why leave it connected and take a chance?? DiagSafe.jpg
 
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krisbee

DTVUSA Jr. Member
#48
The best protection is to simply UNHOOK everything that leads to the outside world by using RF quick disconnects. I use them on my antennas and my DirecTV dish. I have DSL and I unhook the modem from power and from the phone line.
I don't disagree, however, one still has to be cared unhooking and leaving an ungrounded component in the house. Many hams have done this and lightning has jumped from the unconnected coax to wiring several feet away, or the house duct work. Some used to put the leads in a glass jar; this sometimes has caused the jar to explode. Again, the lightning just traveled several miles, a few feet in your house isn't stopping it.

Now, I do this as well, I believe it helps to disconnect, but it is a secondary to the proper grounding. By having the grounding, you are encouraging lightning to stay outside and go into the ground rod, and by disconnecting you are still encouraging it. You gave it a safe place to go, so it does.

Also, BTW, had lightning come in two months ago through the phone line - damaged the DSL (and it is grounded outside with the house ground, only a few feet away from where the connection to the DSL is)... the antenna and computer which were properly grounded were fine. The strike was in the back of one of my pastures, a few thousand feet away - my contention is that the ungrounded few feet of wire from the box into the house (since it was grounded at the box) was enough to induce a charge into my equipment.
 

dth71

DTVUSA Rookie
#51
Ground rod installation questions

Okay

So you guys have me worried enough to get a ground rod installed in the ground.

I have four questions:

1. How the heck am I to get a ground rod 8 feet into the ground? I have enough problems putting up garden stakes 4" into the ground before I hit a nasty rock. (Good old pennsyvannia rock soil)

2. My antenna is connected to a metal j-mount arm on the roof. Do I need to run two seperate copper wires (One for the cable terminal mount and another for the j-mast) as in the drawings? (I picked up a coax terminal block which I intend to attach near the ground.)

3. If I use solid #6 copper wire, can I attach it to the grounding rod with simple metal U clamps? I don't think welding is a possibility here.

4. I have a high quality power surge protector with an lead for antenna inputs. I assume this is to match the antenna lead to the house ground only and not really to protect against spike.
 
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nbound-au

The Graveyard Shift
#52
1. How the heck am I to get a ground rod 8 feet into the ground? I have enough problems putting up garden stakes 4" into the ground before I hit a nasty rock. (Good old pennsyvannia rock soil)
IIRC, its is acceptable to use the mains grounding stake. Others equipment or people can be hired to do the job. An electrician would be a good start.

4. I have a high quality power surge protector with an lead for antenna inputs. I assume this is to match the antenna lead to the house ground only and not really to protect against spike.
Nothing, and I mean nothing, protects against lightning. Im not even sure they connect those boards to house ground for rf (they probably do though), but if you want to do it properly, its not the way you do it.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#53
:welcome: digital_griffin,

I agree 100% with nbound-au. Nothing you can do will protect you 100% from lightning and the advice above in proir posts is excellent.

In my personal situation I am taking advantage of the water pipe entry to my home which I know for certain is steel pipe buried in the ground.

Upon a strike, I am certain the electrical pathway for (the majority of) a lightning strike will go to earth ... but my setup is my choice and not necessarily the right choice for you nor is it necessarily legal per your local building (electrical) code.

IF ... you have any doubt that there is plastic pipe (an insulator) in your water system, my chosen setup is not for you. Secondly, the photos below show I used 12 gauge wire which is not large enough: I didn't have any finger-diameter welding wire on hand, but I now do and I will change it this coming summer.

Jim



 
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SWHouston

Moderator
Staff member
#54
Useing a Water Drill to install a Ground Rod

DG, I fully understand rock you can't see :D Situations like yours, may take several attempts to find a direct route downward through the earth. You need to make a "Water Drill". I have used a 10' piece of 1/2" Schedule 40 black or galvanized pipe, which is threaded on both ends. You then need to go to the Hardware Store, and purchase a 1/2" Female Pipe to 3/4" Male HT (hose thread) adaptor. Screw the HT Adaptor on the Pipe, connect a standard Garden Hose onto the Adaptor. slip the Ground rod up into the pipe, set the open end of the Pipe where you wish your Rod to sink, turn on the water, and let the water pressure wash the dirt out of the way as you put downward pressure on the Pipe. You may hit solid rock on the first attempt. Just move over a few inches and try again. Using the Water Drill, saves pounding your new Ground Rod to pieces, and is much easier than all that hammering. Stop the downward pressure with about 30' (if you use a 10' piece) of the Water Pipe remaining above ground. This should leave about 6" of Rod above the ground. If you are unsure how deep the Rod is, take something small like a thin Steel Measuring Tape and measure down into the 1/2" pipe, BEFORE you pull the Pipe out of the hole, which will leave the Ground Rod in place in the Ground. If you have the capability, using 1/2" Copper Pipe is a bit easier than using Schedule 40. I have provided a link below, which describes this procedure to some extent, save they use Copper Pipe. [video=youtube;htprIppsx70]http://www.youtube.com/watch?v=htprIppsx70[/video]
 
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