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Author Topic: Antenna Ground Wire Installation Dilemma  (Read 8414 times)
KJ4TAX
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Posts: 11




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« on: January 31, 2012, 07:39:10 PM »

Hi Everyone,

I am a new ham with my Technicians license. I am planning to install a chimney mount vertical 2m\70cm antenna which I think I need to run a ground wire to a grounding rod to provide protection in case of a lightening strike. Lightening strikes are not that common where I live compared to other locations in the US. I have looked at some lightening strike maps of the US to verify this. But nonetheless it is cheap insurance should a strike occur. In other words, never say never.

Dilemma #1: My house has a hip roof, i.e. not gabled ends. The eaves of the house, including gutters, have a 14" overhang. I plan to run the ground wire from the antenna mast along the roof and over the eaves down to the grounding rod. This will require that I have a bend in the ground wire where it goes over the roof's edge and back under the 14" eave so I can run the ground wire straight down the wall.

Dilemma #2: Next complicating factor. The prior owner had a sidewalk installed along the backside of the house to connect the carport to the walkout basement steps so I will need to figure out how to install a grounding rod either under the sidewalk. Optionally, I could install the grounding rod about 5 feet away from the house but this would mean I would have to run the ground wire under the sidewalk to the grounding rod, another 90 degree bend. By the way, the grounding rods for my meter is on the back of the house hence I need to bond the grounding rod for the 2m\70cm antenna to the grounding rod for the meter, at least I think I should.

I have read that bends in the ground wire affects its grounding capability. Will this degrade the grounding capability so much that I should not do this?

Thanks for any help.

kj4tax
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NA4IT
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« Reply #1 on: February 01, 2012, 04:34:13 AM »

#1 - Sometimes, that can't be helped. Best practice would be to not have sharp bends in it. You might consider using copper strap made for grounding.

#2 - Have you considered drilling a hole in the concrete large enough to put the ground rod through? You can also get 10 ft ground rods, since the concrete and probably gravel underneath would limit some length of the rod.
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AD4U
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« Reply #2 on: February 01, 2012, 07:59:48 AM »

There is one more thing that I would suggest.  After you install your ground rod in or near the concrete sidewalk, use some #6 or larger copper wire and connect this ground rod to the ground rod that is located near or under the electric power meter. 

The ground rod under your power meter is connected to the electric power system ground grid.  This should (may) greatly increase the effectiveness of your ground system in case of a lightning hit.  It definitely will not hurt anything.

Dick  AD4U
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K9KJM
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« Reply #3 on: February 01, 2012, 08:31:49 PM »

I agree, All "bends" in  a ground conductor need to be gradual, NO sharp bends.  Think bending around a 5 gallon pail....  That is about a 6 or so inch radius and will be fine. Never reverse direction in the ground downconductor.  Keep it heading "down" toward ground. 
Usually a person can bore under a sidewalk with something simple like a slightly bent ground rod with a hole drilled in the end to pull a pull wire through when you pull it out.  Just dig a small hole on each side of the sidewalk and hammer the ground rod horizontally under the concrete, Attach a pull wire and pull the rod back out. Then pull your main ground wire with the pull wire.

#6 copper is mentioned a lot for a ground wire conductor, Also very effective is the flat copper strap mentioned, And so is some soft copper tubing of 1/4" or larger diameter.
(Both can be found at your local discount home supply store, The flat copper strap in the roofing department as roof flashing, And the tubing in the plumbing department. (You want the tubing that comes in long rolls, Not the hard 10 foot lengths)   If you use the tubing, Be careful to not kink it.
(The ground rods can be found at the same home supply store in the electric department, Good 1/2" or 5/8" X 8 foot long are around 10 bucks each.)
For some tips on doing it all on a budget:
 http://www.scribd.com/anon-849269/d/14868226-lightning-protectiontaming-thors-thunderon-a-budget
(Give that site plenty of time to load)

Of all the things you do for lightning protection, Good BONDING of your grounds is the most important.  (Bonding your single point ground panel where the coax enters the building, Mast ground, Electric entrance panel, Telco, Catv, etc all together.)
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W6RMK
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« Reply #4 on: February 01, 2012, 09:20:13 PM »

A few comments..

bend radius isn't all that critical, don't obsess.  There's no good physics reason for bend radii greater than, say, 1" or so.  The code just says as direct as practicable.  Avoid a loop or half loop, though. Electromagnetic stresses will cause issues.

Pay attention to distance of lightning ground from "other stuff".  You don't want it running next to something important (like your coax?)

Strap isn't all that much better than wire for lightning or electrical safety ground.  If you were grounding a 40m vertical, strap is it, but other than that, other things dominate.

All grounds have to be bonded together with AWG6, if you're concerned about code compliance. The inspector wants to see round wire, not tubing, not strap, not braid, not anything other than round wire at least AWG6 or bigger. (there are weird exceptions if you're running the bonding conductor in a conduit and stuff like that)

A bigger question is how you're bringing the coax inside.  Code requires that the shield be bonded to the grounding system at the point of entry.  Good practice says all the "chassis grounds" of everything should be tied together, which implies that your AC wiring ground (green wire) should be connected to the same ground point as your coax shield, etc.

get yourself a free copy of Mike Holt's low voltage grounding book (it's online at the Mike Holt site).. it summarizes all the electrical code requirements nicely, so at least you'll have that part covered.  It doesn't deal with lightning rods or NFPA 780 grounding, if you need that (are you in the 4 call area? the southeast is notorious for high lightning rates.. compared to the very quiet 6 area, for instance)

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K0ZN
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« Reply #5 on: February 02, 2012, 10:45:38 AM »

 Hi.

 You do not want the ground rod right up next to the house, especially if you have a basement. I would recommend placing the rod 8 ft. away from the house.
 The main reason is that there is likely to be more moisture in the soil and thus more conductivity. Well worth the effort and a little additional wire.

 Truly, one ground rod is an absolute rock bottom minimum situation. Two or three, with the other two located at least 8' away and separated from each
 other by 8 ft. would be far more effective. If your soil is dry or rocky, you should use even more rods.

 Remember, you are trying to conduct, literally, MEGA Watts of energy to ground. That amount of energy will saturate the ground around one rod and the energy will be  
 looking for other paths. Ground rods are CHEAP compared to the damage a lightning strike will cause! VERY cheap. If your antenna is the highest thing on top of your
 house, it adds even more urgency. There is also the probability that if you do it right, it will afford some protection to the house. Yeah, it is bad to lose an antenna and
 a rig, but it is a LOT worse to lose all the electronics and some appliances in your house or have the house wiring destroyed. An inadequate ground system to that antenna
 also might void your home owner's insurance.....I am not saying it *will*, but I would not discount the possibility; remember the insurance company does NOT want to pay
 you....they pay claims when they HAVE to. You also might want to think a little bit about upgrading to AWG #4. In the  big scheme of things, that would not be a lot more
 money.  It is all about Risk vs. Reward and you have to make that choice.

Heed AD4U's advise to bond with # 6 to the AC power line ground. VERY important. This keeps the AC line and "your ground" at the same potential.  Also, a very high
percentage of lightning damage comes in on the power line. (When your power line or your neighbor's house is hit!) Adding your ground to the power line ground is nothing but good.

FYI:  I put my money where my mouth is. Since I live in an area that has really bad and frequent lightning in the spring and summer, and I have several HF antenna in the
        yard, I have an extensive system with 14 ground rods (all bonded together) with AWG # 2.

 I am like the other poster; if you actually live in the 4th Call area, you really should take lightning protection seriously. There is no part of the 4th Call area that does not
 have moderately frequent thunderstorms in the warmer months. e.g. Lightning !

73,  K0ZN
« Last Edit: February 02, 2012, 10:51:16 AM by K0ZN » Logged
WX7G
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Posts: 5908




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« Reply #6 on: February 02, 2012, 12:36:20 PM »

National Lightning Safety Institute

http://www.lightningsafety.com/nlsi_lhm/lpts.html

"A single point grounding system is achieved when all equipment within the structure(s) are connected to a master bus bar which in turn is bonded to the external grounding system at one point only. Earth loops and differential rise times must be avoided."

This is what I advocate. The common practice of bringing the coax into the shack via one path turns the house AC wiring into a path for lighting current from the shack to the house AC service ground. A #6 AWG wire paralleling this path will take about half the current with the other half taking the house path. With a 300 kA strike who wants 150 kA through the house?

The solution is to route coaxial cables (you can ground them along the way) first to the AC service ground then to the shack. The house wiring is now hung off the side of the lightning current path and all that the house wiring experiences is displacement current of a few hundred amps (that beats 150,000 amps).
« Last Edit: February 02, 2012, 05:25:17 PM by WX7G » Logged
KJ4TAX
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Posts: 11




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« Reply #7 on: February 02, 2012, 04:59:51 PM »

Thanks to everyone for the advice and the links to more information. I have a lot of reading to do but so far I gather that I need to ground my shack, the antenna mast, coax cable shielding where it enters the shack to the same point where the AC ground from my meter is grounded in order to keep the same potential throughout the grounding system. I need to place any ground rods at least 8ft away from the basement foundation wall. I will use #6 AWG at minimum to bond the the ground system and keep any bends 6 inches or larger in order to reduce the chances of a flashover.

kj4tax
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K0ZN
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« Reply #8 on: February 02, 2012, 07:17:52 PM »


You pretty much have it nailed.  It will seem like kind of a pain type job and maybe expense, but trust me!  When that first heavy thunderstorm rolls over, and
you see those huge, brilliant bolts strike near by and/or hear the house shaking claps, you WILL feel better for the effort. Without spending a pretty fair amount of money,
it is hard to "guarantee" positive results, but you will be far better off than if you do nothing and just BET that nothing will ever happen.

Bottomline: if lightning hits, it WILL go to ground. The only question is through what path!  Generally, giving it what it wants (a low resistance path to ground)
is the best way to guide it to ground.

73,  K0ZN
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W8JX
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« Reply #9 on: February 02, 2012, 08:30:02 PM »

I simply do not share this concern. I have had 3 hits that did damage and several more near hits and NONE of them ever hit a antenna or damaged any radio equipment. (I float them in a storm) Can it happen yes but is it likely to happen here in this scenario? VERY VERY unlikely.
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W6RMK
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Posts: 646




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« Reply #10 on: February 02, 2012, 09:56:55 PM »

Hi.

 You do not want the ground rod right up next to the house, especially if you have a basement. I would recommend placing the rod 8 ft. away from the house.
 The main reason is that there is likely to be more moisture in the soil and thus more conductivity. Well worth the effort and a little additional wire.
on the other hand, depending on where the vapor barrier (if any) is, the concrete in the basement wall might be a good low impedance grounding connector, particularly if it has rebar
Quote
Truly, one ground rod is an absolute rock bottom minimum situation. Two or three, with the other two located at least 8' away and separated from each
 other by 8 ft. would be far more effective. If your soil is dry or rocky, you should use even more rods.
if your soil is rocky and dry, don't fool with ground rods, which have only the virtue of being easy to install, but aren't a very good way to connect anything to the soil.  Use a Ufer ground (concrete encased grounding electrode), specifically developed for dry rocky soil by Herb Ufer.

you might ask yourself why many jurisdictions these days don't allow rods to be the sole grounding means, and actually require a CEGR or simlar.

Quote

 Remember, you are trying to conduct, literally, MEGA Watts of energy to ground. That amount of energy will saturate the ground around one rod and the energy will be  
 looking for other paths.
There is no such thing as "saturating" the ground around a rod.  Yes, if the current density is high enough and the stroke lasts long enough, you'll get a "smoking rod", but that's more likely to happen with something like a utility power line fault to your system (where you can get kiloamps for many minutes).

Megawatts means nothing.. what you are really concerned about is dissipating kilojoules or megajoules.  A megawatt for one microsecond is only one joule (about the energy from dropping an apple a meter).   Lightning strokes last about 50 microseconds.

Quote

Ground rods are CHEAP compared to the damage a lightning strike will cause! VERY cheap. If your antenna is the highest thing on top of your
 house, it adds even more urgency. There is also the probability that if you do it right, it will afford some protection to the house. Yeah, it is bad to lose an antenna and
 a rig, but it is a LOT worse to lose all the electronics and some appliances in your house or have the house wiring destroyed. An inadequate ground system to that antenna
 also might void your home owner's insurance.....I am not saying it *will*, but I would not discount the possibility; remember the insurance company does NOT want to pay
 you....they pay claims when they HAVE to. You also might want to think a little bit about upgrading to AWG #4. In the  big scheme of things, that would not be a lot more
 money.  It is all about Risk vs. Reward and you have to make that choice.

You're confusing a lot of things here. Rods are cheap, but aren't a very good ground. Use them if you have nothing else.  Protecting your electronics doesn't depend on ground rods, it depends on good system design: making sure that lightning current doesn't flow "through" your electronics.  That's more a matter of paying attention to where things are connected (you want to the same point) rather than whether they happen to be at the same voltage as the soil.

Quote

Heed AD4U's advise to bond with # 6 to the AC power line ground. VERY important. This keeps the AC line and "your ground" at the same potential.  Also, a very high
percentage of lightning damage comes in on the power line. (When your power line or your neighbor's house is hit!) Adding your ground to the power line ground is nothing but good.
First part is fine. the code requires (for good reason) that all grounds be bonded together (typically AWG6, but there are other ways).
Connecting your antenna ground to the power line ground doesn't necessarily help with transients, but it is required for other reasons.
Quote
FYI:  I put my money where my mouth is. Since I live in an area that has really bad and frequent lightning in the spring and summer, and I have several HF antenna in the
        yard, I have an extensive system with 14 ground rods (all bonded together) with AWG # 2.

 I am like the other poster; if you actually live in the 4th Call area, you really should take lightning protection seriously. There is no part of the 4th Call area that does not
 have moderately frequent thunderstorms in the warmer months. e.g. Lightning !

73,  K0ZN
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K0ZN
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Posts: 1525




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« Reply #11 on: February 03, 2012, 11:57:20 AM »


 W6RMK....

 I intended this post to be SIMPLE to help out a new ham, NOT an extensive, detailed, engineering design proposal with footnotes. 
 
 Next time, I will run my posts through the IEEE for technical editing.

 The LAST thing I would do is put a ground rod(s) up close to my foundation structure.

73,  K0ZN
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W6RMK
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« Reply #12 on: February 03, 2012, 06:19:46 PM »

perhaps not so oddly, most ground rods are driven next to the foundation, because you want the path from "thing being grounded" to "ground" to be as short as possible.  Putting it next to the foundation also means that it's less likely to be disturbed (by mowers, brush trimming, painters dragging ladders, who knows what all). That doesn't change that ground rods, as a grounding means, are less than ideal.

Most of us don't have infinite money and time, so it's worth spending those resources wisely, in accordance with sound engineering and physics principles.  There's a fair amount of  bad advice out there.  There's also a whole lot of misconceptions out there that while not actively bad, cause people to spend time and effort in ways that are ineffective. Some are drawn from applications which are similar, but different in important ways (lightning grounds are not HF antenna grounds are not 60 Hz power line grounds).  Some are historical, are not recommended in light of modern knowledge, and deserve a peaceful retirement. 

Since you mention the IEEE, they actually have several books on grounding, but the so-called "emerald book" (IEEE-1100) is the one most applicable to hams.  It's fairly straightforward, has been reviewed by people whose life work is in the field, etc.. It covers all the kinds of grounding and bonding.  It's pricey to buy, but you can request it from your local library.

For free, I'd recommend the Mike Holt Low Voltage Grounding book.  Download it from http://www.mikeholt.com/ and it tells you pretty much everything you need to know about grounding for amateur radio installations (and low voltage control, like that rotor control) from an electrical code standpoint.  The actual electrical code (NEC - NFPA70) from the NFPA  isn't readily available on the web, but Carl Malamud has most of the codes online at https://public.resource.org/index.html or more specifically at http://bulk.resource.org/codes.gov/   (Florida doesn't have an electrical code apparently, but if you look at California's, it's basically a copy of the NEC).  It's just a giant pdf, and doesn't have all the nice notes and links you'd get if you forked over the $125 to NFPA.   You're interested in Article 250 (grounding), and the 800's (all the antenna stuff).

If your insurance requires it, then NFPA 780 is the standard for lightning protection.  There's a copy out on the web at New Mexico State University, I think.

And, of course, the ARRL handbook does have a section on grounding, recently revised.
 
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KJ4TAX
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« Reply #13 on: February 03, 2012, 06:33:53 PM »

I appreciate everyone's input. I will take a look at Mike Holt's info. My basement wall is cinder block (hollow). My house was built in 1959 so the AC is not grounded to the basement slab. Also the soil here is mostly clay, only about 4 inches or so of top soil. The clay is pretty dense so I will have to use a hammer drill to drive ground rods. I will make sure I ground everything to the same point which is where the house AC is grounded. If I drill extra rounds I will make sure I bond everything together.

kj4tax
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KF4WXD
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« Reply #14 on: February 10, 2012, 11:41:07 AM »

There is one more thing that I would suggest.  After you install your ground rod in or near the concrete sidewalk, use some #6 or larger copper wire and connect this ground rod to the ground rod that is located near or under the electric power meter. 

The ground rod under your power meter is connected to the electric power system ground grid.  This should (may) greatly increase the effectiveness of your ground system in case of a lightning hit.  It definitely will not hurt anything.

Dick  AD4U

It's not just a good idea, it's the law.  The NEC specifies that all grounding systems are to br bonded to the electrical service safety ground.

Russ - kf4wxd
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