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Author Topic: Yes, more questions about grounding  (Read 1975 times)
N8EUI
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« on: July 26, 2009, 08:19:19 AM »

I have some questions about lightning grounds I hope someone can answer.  
 
I am erecting a Butternut HF-9V vertical antenna in my backyard.  In addition to a thorough wire radial system, I will be installing an eight foot copper clad steel ground rod connected to its base.  In addition, outside my coax entrance to my house, I'm installing a lightning arrester mounted to another ground rod (the arrester mounts onto a mounting block which in turn mounts onto the ground rod and the feedline enters the house).  I am also installing another ground rod as a ground for my equipment.  Of course my AC power is also grounded at the service entrance.  My question is: Will this suffice for my grounding needs?  I've read the AC mains and telephone service grounds need to be grounded to my antenna ground, too.  If this is true how do I bond them together?  Do I run a heavy guage wire from the AC service ground back (about six feet) to the ground rod that enters the house?  Why must the antenna be grounded together with the AC/Telco ground?  If my antenna was to be hit by lightning, either directly or indirectly, why would I want the energy to dissipate through my AC mains and telephone?  I hope you can answer these questions and direct me in the right direction.
 
Thank you,
 
Tom, N8EUI
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AA4PB
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« Reply #1 on: July 26, 2009, 10:29:51 AM »

The National Electric Code (NEC) *requires* that your station grounds (antenna, rig, etc) be "bonded" to the electrical system ground with a minimum #6 wire. The primary reason is to prevent an electrical shock hazard in the event that the two grounds wind up at different voltage levels. This can often happen due to leakage currents in electrical equipment grounds.

It is also good practice to connect all ground wires coming into the house (electrical, antenna, cable, phone, etc) to a single point ground. During a lightning event all grounds will then rise to the same voltage, preventing current from flowing through equipment connected to the different grounds. For example, lets say a nearby lightning strike causes current to be coupled into the electrical lines. Lets say that the grounds are not bonded together and your antenna ground is lower impedance that the electrical ground. Some of the current will then flow from the electrical system through your radio and coax on its way to the more effective antenna ground. If you provided a heavy duty bond between the grounds then most of the current would flow through that bonding wire in lieu of the radio and coax.
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K1CJS
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« Reply #2 on: July 26, 2009, 10:31:07 AM »

Sounds pretty good--but you MUST tie the electrical service ground to your antenna system ground.  The reason is that you want all parts of the building ground system to be at the same electrical potential.  Even through the earth, there is resistance between ground rods.  

Say there is an excess of static electric charge on your antenna system, including the antenna ground system.  If the electrical ground is at a different potential, say more positively charged, and you're in the shack working the bands, that charge can go through your equipment--and possibly through you.

That is the reason the grounds must be tied together--for safety.
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K9KJM
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« Reply #3 on: July 27, 2009, 12:37:20 AM »

Didn't you just ask this same question over in the Elmers section???

Here is the reply from there:

RE: Yes, more questions about grounding  Reply  
by K9KJM on July 27, 2009  Mail this to a friend!
 
The basic concept of proper lightning protection is to BOND all grounds together with a heavy bare copper conductor. (#6 copper minimum, Flat copper strap is even better) (Tower, Mast, AC power entrance, Telco, Cable TV, etc.)

Try to space your ground rods about twice the distance apart as the depth. (8 foot deep rods should be spaced about 16 feet apart.)(It will not hurt to space them closer together, You just lose effectiveness, And in effect are "wasting" a ground rod.)

For some good information about proper protection:

http://members.cox.net/pc-usa/station/ground0.htm

Grounding your coax shields before they enter the buildings somehow is a must.

The actual "lightning arrestor" used in the overall scheme of things is about the least important item.
Proper grounding and bonding is much more important.

Article in the May 2009 issue of Popular Communications magazine with tips on how to do it all on a budget.
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N8EUI
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« Reply #4 on: July 28, 2009, 07:56:38 PM »

Thank you all for the information. I now have a clearer understanding about bonding all grounds.

Tom, N8EUI
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WA7VTD
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« Reply #5 on: September 08, 2009, 09:02:04 AM »

A single point ground is the best and should be used, and it sounds just great. But practically speaking, what does one do when one's AC service ground is located some 60 linear feet, on the other side of the house, from one's antenna feedline bulkhead? Is No. 6 wire running from one to the other really effective? In theory, ought it not be very wide copper strap? What is the best solution for this problem, and what is the next best alternative to single point ground?

Thanks,

Kevin H. WA7VTD
Oregon City, OR
licensed in 1973 (WN7VTD)
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AA4PB
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« Reply #6 on: September 08, 2009, 03:23:35 PM »

Yes, its still effective in making sure that you don't have a shock hazard caused by grounding systems with a voltage difference between them. The NEC doesn't make any exceptions for systems being on opposite sides of the house.
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W8JI
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« Reply #7 on: September 09, 2009, 04:20:35 AM »

It is NOT necessary to ground the radial system of a remote antenna to the mains. As a matter of fact that is almost silly unless the radials come right up to the mains ground. If the antenna was on or next to the house it should be tied in. If the radials come up to the house they should probably be tied in. Running a separate conductor out to the antenna however is largely a waste of time.

What the code says is everything entering or leaving the building must be bonded to a common ground point with the mains, and that is what will also stop lightning damage.

My towers get direct hits several times a year here with direct hits and I never have damage. I don't even have a lightning arrestor on any coaxial lines. My towers certainly are not bonded to the mains, except through the feedline shields at the entrance. My TV tower is, but it is one foot from the house.

Tom
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AA4PB
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« Reply #8 on: September 09, 2009, 05:31:03 AM »

what does one do when one's AC service ground is located some 60 linear feet, on the other side of the house, from one's antenna feedline bulkhead
------------------------------------------------------
It sounds to me like he's talking about the single point ground for the feed lines entering the house so YES it is still important to bond that system to the electrical system ground - even if it's 60 feet away.
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AA4PB
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« Reply #9 on: September 09, 2009, 05:37:12 AM »

And from the Polyphaser web site:

"The tower ground system and the single point ground system must be interconnected. This interconnection should be below grade and with a bare low inductance conductor. The coax cable shield must not be the only interconnection between ground systems."
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WB5JEO
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« Reply #10 on: September 09, 2009, 03:02:37 PM »

"what does one do when one's AC service ground is located some 60 linear feet, on the other side of the house, from one's antenna feedline bulkhead"

There are several things involved in this. It's a not an uncommon situation. Few can or are able to do a textbook job of it, which would be ground systems properly done at both ends and well bonded together. I think, though, that a reasonable effort can do a lot to deal with the two concerns, an impulse originating in the utility mains and an impulse originating in the antenna system. Each should be offered a good ground that we hope will soak up the impulse from either source and not leave one or the other as an attractive path. It's not quite getting the whole system, mains, house wiring, shack wiring, and antenna system to the same potential, but it may be the best effort that can be made. Like so much in lightning protection, you have to recognize where a less than ideal system is vulnerable and evaluate the risk of the particular events where that vulnerability can do harm.

I have something like that. The shack is an outbuilding some 100 feet from the house. Even if I were to undertake the project of bringing both ends to the same ground, it would take a while. The ground is very rocky and difficult to drive rods into and much worse than other soils for trenching. I deem strikes and near strikes to the tower to be the more likely hazard to the radio equipment, but I also know it's something of a crap shoot whether any particular event happens at all or affects things on the far end of the action. So I treat the shack as I would an individual house and the house as a house and the power feed to the shack as a commercial main and consider it a reasonably practical approach.

The answer to the in-house shack on the far side from the service panel and mains involves making these same choices. Unquestionably, the house would benefit (if it came to a major event) from a proper ground system that included appropriately spaced, sized, and bonded rods around the house perimeter, part of which would pass close to the shack SPG panel. But the important thing is, I think, to consider the effect of well-grounded radio system that's powered by house power that likely has the typical one-rod "safety ground" that can see one good ground path, the one through the equipment. But at least recognize that the typical house wiring ground isn't adequate for a large impulse and balance that against the reality that major events are not very common.

The problem with discussions of lightning protection is that stories of others' experiences mean little, and even following advice to do nothing at all may work out just fine, if nothing happens or what happens does no harm. The best advice may be to learn as much as you can, do as much as you're willing or able to do that doesn't do more harm than good, and buy insurance. Reference is often made to commercial installations where large sums were spent on protection, but it's rarely considered that those folks likely still still buy insurance.
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KB9CRY
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« Reply #11 on: September 09, 2009, 04:17:18 PM »

I've read the AC mains and telephone service grounds need to be grounded to my antenna ground, too.

Yes, this is a big must and maybe the most critical part of a properly designed and installed grounding system.  Read on.

If this is true how do I bond them together? Do I run a heavy guage wire from the AC service ground back (about six feet) to the ground rod that enters the house?

Yes, min #6, I use #4 bare solid copper wire.  Use either mechanical clamps or exothermic connections.

Why must the antenna be grounded together with the AC/Telco ground?

Read on......

If my antenna was to be hit by lightning, either directly or indirectly, why would I want the energy to dissipate through my AC mains and telephone? I hope you can answer these questions and direct me in the right direction.

The energy will not go through the AC mains or phone.


Take a step back and look at your house from afar.  You have this strike energy being induced in some part of your system, either via the antenna or via the AC wires or the phone system.  The energy causes a voltage rise to occur.  When everything is bonded to each other, as described, everything rises in voltage potential to ground together and falls in voltage potential to ground together.  If you didn't have everything bonded to each other, there would be a voltage potential difference somewhere in the system.

Now, back to basics, "What does a voltage potential difference create?"   The answer is current.  And having a current in your system, it deadly to electronic components and may cause a fire.

Get it?  Everything is bonded and in the induced energy state, everything rises and falls in potential voltage together and therefore no current and no damage.  Voila!   QED
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K9KJM
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« Reply #12 on: September 09, 2009, 11:46:47 PM »

Yep, CRY is correct.
For some good info:

http://members.cox.net/pc-usa/station/ground3.htm

(Note that there are many pages and links to go to on that site)
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W8JI
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« Reply #13 on: September 11, 2009, 05:12:25 AM »

Polyphaser has good information, but it is not absolute for every installation. They mostly assume all towers or antennas are in a small radius near the building.

If a ground system or antenna is somewhat remote or remote from the building, there is no reason for a ground to ground interconnection. Just follow the entrance rules and all is safe.

You can see my grounding here:

http://www.w8ji.com/ground_systems.htm

Note I have NO lightning arrestors in any coaxial line. I have silver soldered or bolted connections. My tallest tower, over 300 feet tall, normally takes dozens of hits a year. On occasion shorter towers, like the 220 ft towers, will get hit. All of my gear stays connected 24/7, all of our TV's  and computers stay connected, and nothing internal ever gets damaged.

This shows the advantage of proper common point entrances alone.

Tom
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AA4PB
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« Reply #14 on: September 11, 2009, 06:07:02 AM »

Tom, you obviously do not have this situation but I have seen situations (one in a military antenna range) where there was a voltage difference between the building system ground and the remote tower site ground. When you removed the coax connector you would see small sparks and could get a slight shock if you weren't careful. Running a heavy wire (as Polyphaser recommends) between the tower site ground and the building single point ground solved it by ensuring that there was a permanent low resistance connection between the two. As Polyphaser says, don't depend on the coax shield as the ONLY connection between the two grounds.

Over the years I've also seen the same thing at several ham stations, which is why I immediately recognized the source of the problem at the test site. While it may not always be needed, I don't see any reason not to bond the tower ground and the station single point grounds together to be on the safe side.

73,
Bob
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