Survivalist Forum

Advertise Here

Go Back   Survivalist Forum > Survival & Preparedness Forum > DIY - Do It Yourself
Articles Chat Room Classifieds Donations Gallery Groups Links Store Survival Files



Advertise Here
Reply
 
Thread Tools Display Modes
Old 10-11-2011, 11:46 AM
AlgoRhythms's Avatar
AlgoRhythms AlgoRhythms is online now
Old Noob
 
Join Date: Sep 2008
Location: Pennsylvania woodlands
Posts: 4,769
Thanks: 2,490
Thanked 5,218 Times in 2,401 Posts
Default Antenna mast lightning protection



Advertise Here

I want to attach a 12 foot steel mast to the peak of my house in order to support a professional wireless weather station.

Naturally, I'm concerned about lightning strikes so I'm looking for suggestions for proper grounding.

Any help is appreciated.

Thanks!
Old 10-11-2011, 01:03 PM
6556 6556 is offline
human
 
Join Date: Nov 2010
Posts: 2,578
Thanks: 207
Thanked 2,462 Times in 1,167 Posts
Default

Many years ago I worked in the TV repair/antenna installation business.
When it comes to grounding antennas, there have always been two schools of thought.

The better the ground, the better the chances are that any damage as a result of a lighting strike will be minimized.

and..

The better the ground, better the chances are that it WILL be struck by lighting.

Fact is, both are true.

Most TV antennas were grounded with a single #14 plastic coated copper or aluminum wire. Fact is, this size wire will never be capable of handling the current generated by a lighting strike.
In addition, this wire is normally attached to a 10 foot copper ground rod, which normally isn't sufficient by it's self to disperse the charge from a lighting strike.

I've seen the result of a lighting strike on a "grounded" antenna. All that remained of the ground wire was a "burnt" trail. Where the wire ran under a rain gutter the lighting jumped to the gutter and knocked it off the house and had long sections of it burnt off. Areas of the side of the house (painted wood) had a large "spider web like" burn mark. The TV and antenna rotor were a total loss as were the stereo system and transformers for the door bell and furnace thermostat.
The funny thing about this particular strike was that it occurred only a week after a new antenna was installed. The OLD antenna was never grounded, and during it's 30 years of service was never hit by lighting.

For a good ground you really need a couple of ground wires the size of welding cables double ought #00 tied to a "field" of ground rods that are driven into a moist/wet ground, and even then a strike could damage your electronic equipment attached to your pole.

The purpose of grounding a antenna/pole on the roof is to prevent your house starting on fire, and not to "protect" any electronics tied to it.
The Following 5 Users Say Thank You to 6556 For This Useful Post:
Old 10-11-2011, 01:18 PM
AlgoRhythms's Avatar
AlgoRhythms AlgoRhythms is online now
Old Noob
 
Join Date: Sep 2008
Location: Pennsylvania woodlands
Posts: 4,769
Thanks: 2,490
Thanked 5,218 Times in 2,401 Posts
Default

Thanks. It's very helpful. I am not worried about the electronics that are attached to the pole. I'll have no wires to anything inside as the weather station is wireless.

I'm primarily concerned with minimizing damage done to my home and the possibility of voiding my homeowner's insurance by "attracting" a lightning strike and not providing a proper ground path.
Old 10-11-2011, 03:06 PM
barter411's Avatar
barter411 barter411 is offline
Newbie
 
Join Date: Oct 2011
Location: Central New York
Posts: 10
Thanks: 4
Thanked 6 Times in 4 Posts
Default

I attached a bare stranded copper ground wire to the top of the steel mast. Not sure the gauge. It should be as vertical as possible. No sudden jogs. Drive a copper stake into the ground immediately below and attach with a clamp. Mine is eight feet deep. It is stapled along the main house post inside the wall. In case of a strike, I understand it could completely melt the copper wire, but hopefully no fire.
The Following User Says Thank You to barter411 For This Useful Post:
Old 10-11-2011, 05:49 PM
Grinner Grinner is offline
Member
 
Join Date: May 2011
Posts: 49
Thanks: 48
Thanked 54 Times in 20 Posts
Default

I wouldn't intentionally attract lightning to anything attached to my house. I had a lightning strike a tree next to my house. The surge followed a root to the grounding rod of the phone cable. The surge not only went into the ground from there, but also followed the phone cable inside. Blew the phone box straight off the wall in the kitchen, shattering the plastic box. Some of the plastic landed in the toaster in the kitchen. This was extremely violent. There was no fire, but the wiring was charred.

In my view, antennas should not be mounted on or near a house.
The Following 2 Users Say Thank You to Grinner For This Useful Post:
Old 10-11-2011, 08:48 PM
6556 6556 is offline
human
 
Join Date: Nov 2010
Posts: 2,578
Thanks: 207
Thanked 2,462 Times in 1,167 Posts
Default

Quote:
Originally Posted by Grinner View Post
I wouldn't intentionally attract lightning to anything attached to my house. I had a lightning strike a tree next to my house. The surge followed a root to the grounding rod of the phone cable. The surge not only went into the ground from there, but also followed the phone cable inside. Blew the phone box straight off the wall in the kitchen, shattering the plastic box. Some of the plastic landed in the toaster in the kitchen. This was extremely violent. There was no fire, but the wiring was charred.

In my view, antennas should not be mounted on or near a house.
But ... that antenna lead in wire.. where does it go? And on top of that.. the longer the lead in wire the more loss of signal to your receiver.
Old 10-12-2011, 12:41 AM
Grinner Grinner is offline
Member
 
Join Date: May 2011
Posts: 49
Thanks: 48
Thanked 54 Times in 20 Posts
Default

Good questions. If it were me, I would free-stand the antenna, ground the mast really well (as Barter411 describes above), and just run whatever cable you need into your house. Not sure what type of cable you have to use, but RG-6 coax cable, for example, can run for a good distance (100 ft or more) without any significant signal loss.

I wouldn't have wanted the lightning to strike something attached to my house. That means it would go through the house to the ground. If the cables are run through walls, that can mean fire inside walls. Not good. Ancillary damage to devices connected to whatever gets hit by lightning is fine, but I don't want to attract lightning to strike my roof or my house.
Old 10-12-2011, 12:59 AM
6556 6556 is offline
human
 
Join Date: Nov 2010
Posts: 2,578
Thanks: 207
Thanked 2,462 Times in 1,167 Posts
Default

In this application, it's wireless. no lead in required.
Old 10-12-2011, 09:06 AM
AlgoRhythms's Avatar
AlgoRhythms AlgoRhythms is online now
Old Noob
 
Join Date: Sep 2008
Location: Pennsylvania woodlands
Posts: 4,769
Thanks: 2,490
Thanked 5,218 Times in 2,401 Posts
Default

Quote:
Originally Posted by 6556 View Post
In this application, it's wireless. no lead in required.

Thank you for noticing this!
Old 10-12-2011, 10:30 AM
westom westom is offline
Newbie
 
Join Date: Sep 2009
Posts: 22
Thanks: 0
Thanked 9 Times in 6 Posts
Default

Quote:
Originally Posted by 6556 View Post
In this application, it's wireless. no lead in required.
Earth that pole as required by the National Electrical Code. And exceed what code requires. For example, a connection from pole to earth must be as short as possible. No sharp wire bends. No splices. Wire not inside any metallic enclosure.

That pole does not make lightning strikes more frequent. That popular myth is only from hearsay. Lightning will strike something. Better earthing of a pole means lightning strikes the pole - and not your house. That pole is nothing more than a lightning rod if properly earthed. Either it connects lightning harmlessly to earth. Or it connects lightning to something else - destructively. Quality of earthing for that pole is your most important consideration.

Surges only do damage when incoming and outgoing via something. If both paths do not exist, then no damage exists. If a surge is incoming to the weather station but has no outgoing path, then no damage. If a surge has any reason to pass through that weather station on a connection to earth, then the station is damaged. Essential is for the station to be mounted so that an electrical path through that station is inferior to an electrical path around that station.
The Following 2 Users Say Thank You to westom For This Useful Post:
Old 10-12-2011, 10:48 AM
AlgoRhythms's Avatar
AlgoRhythms AlgoRhythms is online now
Old Noob
 
Join Date: Sep 2008
Location: Pennsylvania woodlands
Posts: 4,769
Thanks: 2,490
Thanked 5,218 Times in 2,401 Posts
Default

Quote:
Originally Posted by westom View Post
Earth that pole as required by the National Electrical Code. And exceed what code requires. For example, a connection from pole to earth must be as short as possible. No sharp wire bends. No splices. Wire not inside any metallic enclosure.

That pole does not make lightning strikes more frequent. That popular myth is only from hearsay. Lightning will strike something. Better earthing of a pole means lightning strikes the pole - and not your house. That pole is nothing more than a lightning rod if properly earthed. Either it connects lightning harmlessly to earth. Or it connects lightning to something else - destructively. Quality of earthing for that pole is your most important consideration.

Surges only do damage when incoming and outgoing via something. If both paths do not exist, then no damage exists. If a surge is incoming to the weather station but has no outgoing path, then no damage. If a surge has any reason to pass through that weather station on a connection to earth, then the station is damaged. Essential is for the station to be mounted so that an electrical path through that station is inferior to an electrical path around that station.

Good post. Thanks.

Here's the rub. I don't think its possible to have a sufficient ground path to direct a lightning strike harmlessly to earth. I have limits as to what wire gauge I can comfortably work with (#4? #2?) and practical concerns with installation. There is also a financial limit as to what I can spend.

I agree, though; exceed the code.

I'm hoping that the taller oak trees nearby will be more likely to attract a potential strike.

And you are also correct to mention isolating the weather station from the mast, although a direct hit will certainly arc across any insulator I use.
Old 10-12-2011, 10:57 AM
Robot's Avatar
Robot Robot is offline
Survivor
 
Join Date: Feb 2009
Location: Twilight Zone
Posts: 7,958
Thanks: 22,068
Thanked 11,686 Times in 4,425 Posts
Default

Lightning is ugly, period.
Old 10-12-2011, 10:57 AM
REM's Avatar
REM REM is offline
Getting There!
 
Join Date: Oct 2008
Location: East Texas
Age: 56
Posts: 8,743
Thanks: 14,849
Thanked 11,714 Times in 4,902 Posts
Default

Quote:
Originally Posted by AlgoRhythms View Post

Here's the rub. I don't think its possible to have a sufficient ground path to direct a lightning strike harmlessly to earth. I have limits as to what wire gauge I can comfortably work with (#4? #2?) and practical concerns with installation. There is also a financial limit as to what I can spend.
This is a small town and it might differ from where you are.

The utility company gives away old wooden poles. They don't remove the heavy copper ground wires. I'm not sure what gauge this solid conductor is, but it's what grounds each pole in the field.

I got quite a bit years ago. We went and got used poles to make a large pole barn. With copper at a premium this might no longer be the case.

I'm pretty sure that I've seen the same solid copper wire at Lowes.

All that you're trying to do is to go from the top of the mast straight down to a ground rod, or to a series of ground rods, right? As in 12-20 feet of ground wire?
The Following User Says Thank You to REM For This Useful Post:
Old 10-12-2011, 11:02 AM
westom westom is offline
Newbie
 
Join Date: Sep 2009
Posts: 22
Thanks: 0
Thanked 9 Times in 6 Posts
Default

Quote:
Originally Posted by AlgoRhythms View Post
I don't think its possible to have a sufficient ground path to direct a lightning strike harmlessly to earth. I have limits as to what wire gauge I can comfortably work with (#4? #2?) and practical concerns with installation. There is also a financial limit as to what I can spend.
Many use 6 AWG bare and solid copper wire. You have no choice. You must earth the pole. Otherwise even your insurance company may decide after some future event to not honor your policy.

Some numbers. How much current can an 18 AWG (lamp cord) wire conduct? That wire is rated for 10 amps because it will conduct 60 amps continuous. And something approaching 60,000 amps surge current. Obviously, a 6 AWG wire will conduct more. A typical lightning strike is about 20,000 amps.

Conductivity is not so much about wire thickness (resistance). Conductivity is mostly about wire length (impedance). And other factors that would negatively increase that impedance (ie sharp wire bends).

Most important is quality of the earthing electrode. Even geology is relevant.

I never said isolating it from the mast is important. I said a path to earth must be so conductive as to not pass through the weather station. One best connection to the mast is a single point connection. A single point connection between mast and station means no incoming and outgoing path. Insulation can or might not exist. Either way, insulation is not relevant since even insulators are conductors of this electricity. Station is located in a manner where the connection from cloud to mast is also not via the weather station.
The Following User Says Thank You to westom For This Useful Post:
Old 10-12-2011, 11:17 AM
REM's Avatar
REM REM is offline
Getting There!
 
Join Date: Oct 2008
Location: East Texas
Age: 56
Posts: 8,743
Thanks: 14,849
Thanked 11,714 Times in 4,902 Posts
Default

And the taller oak trees...

Trees are likely to take the strike, as they are tall and have a moisture content.

They (trees) are not good conductors, though. Side flash is what happens when a better conductor is near a tree that is hit. In my parents case it was a chain link fence a few feet away from a large oak tree on the neighbors property. The surge jumped to the fence and took out most of my parents appliances. The tree pretty much exploded, as it's not a good conductor.

What I did here is to leave the temporary electric pole that was used during construction. I got up and bolted an 8 foot grounding rod to the top and used the solid copper grounding wire to the grounding rod for the temp pole. This will, I hope, serve to catch any side flash should these trees be hit by lightening. This is directly between the vulnerable trees and the large metal box where my juice (buried) comes into the house.



Comments? This is a separate ground rod from my main, which is about 12 feet away.
The Following User Says Thank You to REM For This Useful Post:
Old 10-12-2011, 02:22 PM
6556 6556 is offline
human
 
Join Date: Nov 2010
Posts: 2,578
Thanks: 207
Thanked 2,462 Times in 1,167 Posts
Default

---------"Some numbers. How much current can an 18 AWG (lamp cord) wire conduct? That wire is rated for 10 amps because it will conduct 60 amps continuous. And something approaching 60,000 amps surge current. Obviously, a 6 AWG wire will conduct more. A typical lightning strike is about 20,000 amps."----------------

I guess I can't get past this statement. I can believe that a 18 AWG wire can pass (safely) 10 amps. But to say it's rated at 10 amps BECAUSE it will conduct 60 amps continuous? I couldn't imagine pulling 60 amps thru 18 gauge wire for any extended period of time. My understanding of the term "continuous" is the same as 100% duty cycle. I would think that under these conditions that that wire would be glowing like a light blub. Then there is the 60,000. amp "surge" Using surge in the electrical jargon may include the surge current that a motor might draw.

Depending on the motor and it's load this "surge" could last as long as a few seconds.
Anyone seeing "18 AWG" "60,000 amps" and "surge" used in the same sentence sure could get themselves in a world of HURT!.


I'm temped to believe that 18 AWG can pass 60,000 amps but only if the time frame is in the nanosecond range (hardly what I would call surge). Even then I would expect that the wire would light up like the sun.


Then this ---------------------"Conductivity is not so much about wire thickness (resistance). Conductivity is mostly about wire length (impedance). And other factors that would negatively increase that impedance (ie sharp wire bends)."--------------------

I certainly understand the relationship between wire length and impedance when used in context with frequency. But I'm lost when impedance is mentioned when discussing the current flow as a result of a lightning strike, since frequency is Zero (DC). How does one address impedance when one is grounding a "pole" on a roof if it's a one story, two story.. or a 100 story building?


------------"The tree pretty much exploded, as it's not a good conductor"------

When it comes to the "potential" of a lighting strike a tree really is a good conductor. The tree exploding is a result of the moisture (tree sap) heating up past it's flash point (turns to steam) and the resulting pressure "vents".

No one (in their right mind) would ever try to predict where and how a the current (of a lighting strike) will flow. I've heard stories where a bolt hitting a tree jumped to a fence, which then jumped to a clothes line to a house where it then jumped to a child's wagon and wielded the wheels to the axles.
There was a 400 foot communication tower near by, yet it was the tree that was hit.
The Following User Says Thank You to 6556 For This Useful Post:
Old 10-13-2011, 12:52 AM
westom westom is offline
Newbie
 
Join Date: Sep 2009
Posts: 22
Thanks: 0
Thanked 9 Times in 6 Posts
Default

Quote:
Originally Posted by 6556 View Post
I guess I can't get past this statement. I can believe that a 18 AWG wire can pass (safely) 10 amps. But to say it's rated at 10 amps BECAUSE it will conduct 60 amps continuous? ... Using surge in the electrical jargon may include the surge current that a motor might draw.
Unfortunately confusion always occurs when every term is not defined in numbers. A 60 amp wire is only rated at 10 amps for many reasons (numbers) that are well beyond the scope of this discussion. But more relevant is how many surge amps it can conduct. Which says why 6 AWG wire is sufficient to earth direct lightning strikes. Those numbers only provided to explain what size wire is sufficient for conducting surges.

Surges are microsecond events from a current source. Another completely different event, that you are also calling a surge, is a so much longer (millisecond plus) current demanded from a voltage source. Two cmpletely different electrical events defined by a common word. And an example of why subjective reasoning so often results in junk science conclusions.

Context (and associated numbers) dictates the relevant surge is the first one - a microseconds event. (Context also says another surge called a flood is also irrelevant.) Relevant here are many thousands of amps for microseconds. A transient that, if not connected to earth, will then increase voltage destructively to obtain earth. Another characteristic unique to this type of surge.

It is not DC as you have assumed. Why does lightning cause radio reception interference? Because this surge is a wide spectrum of radio frequencies. More reasons why impedance (not resistance) is critically important.

Where that pole is located does not change one important consideration. It must be earthed. Especially when on a roof. A wire may be required to make a direct (lowest impedance) connection to what absorbs energy - the earthing. But more important is what is the art in this discussion. And that defines quality of the entire system. Earth ground.

Another example. Lightning obtain earth by striking a tree. 30 feet away, lightning killed a cow. Was that cow killed by induced fields? Many who know only from assumptions would assume so. The cow was also directly struck.

Lightning is a connection from a cloud to earthborne charges maybe 5 miles away. What is the shortest electrical path? 3 miles down to the tree. And four miles through earth. However, that shortest path was also up the cows hind legs and down its fore legs. Cow was killed by a direct lightning strike that also struck the tree. Another example of why earthing is an art. Had that cow been surrounded by a buried wire loop, then it may have survived.

Many who know only from hearsay or observation would assume lightning is capricious. The problem is also infrequent. Welcome to an art: making direct lightning strikes irrelevant.
The Following 2 Users Say Thank You to westom For This Useful Post:
Old 10-13-2011, 05:33 AM
z96Cobra z96Cobra is offline
Jack of all trades
 
Join Date: Sep 2008
Location: Indiana
Posts: 225
Thanks: 56
Thanked 381 Times in 111 Posts
Default

What weather station do you have? Do you have a better place to mount it than the roof? Directly above the roof (even 12') can give inaccurate readings of temperature, and wind speed/direction. I've been running a Davis Vantage Pro station since 2004. My site isn't ideal but I've been too cheap/lazy to mount my anemometer at the correct height. Check out these links for siting info

http://www.nws.noaa.gov/om/coop/standard.htm

http://www.rmets.org/pdf/guidelines/aws-guide.pdf
The Following User Says Thank You to z96Cobra For This Useful Post:
Old 10-13-2011, 08:24 AM
AlgoRhythms's Avatar
AlgoRhythms AlgoRhythms is online now
Old Noob
 
Join Date: Sep 2008
Location: Pennsylvania woodlands
Posts: 4,769
Thanks: 2,490
Thanked 5,218 Times in 2,401 Posts
Default

Quote:
Originally Posted by z96Cobra View Post
What weather station do you have? Do you have a better place to mount it than the roof? Directly above the roof (even 12') can give inaccurate readings of temperature, and wind speed/direction. I've been running a Davis Vantage Pro station since 2004. My site isn't ideal but I've been too cheap/lazy to mount my anemometer at the correct height. Check out these links for siting info

http://www.nws.noaa.gov/om/coop/standard.htm

http://www.rmets.org/pdf/guidelines/aws-guide.pdf
I'm also using a Davis Vantage Pro. I started with a mount I made with PVC pipe but it's too low. I'm pretty much limited for locations.
Old 10-13-2011, 10:19 AM
rearden rearden is offline
Newbie
 
Join Date: Oct 2011
Posts: 5
Thanks: 0
Thanked 3 Times in 3 Posts
Default

1. Improve your house ground by putting in several more ground rods twice their length apart in a star fashion. Bind them together with buried #8 bare.
2. Bind ALL grounds (electric, phone, cable, etc.) for the house together.
3. Where the cables for tower enter the house place surge protection for _all_ wires and ground them to the ground rods with copper strap (not wire).
4. Consider a whole house surge protector in main distribution panel. (1st line of protection). Intermatic, Siemans, etc.
5. Practice single point grounding on what will be plugged into what goes to the tower. As in _everything_ connected to the device have all the wires go through a surge protection device like an IsoBar.
The Following User Says Thank You to rearden For This Useful Post:
Reply

Bookmarks



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
EMP and Lightning gkmiami Disaster Preparedness General Discussion 4 08-13-2010 05:32 PM
Antenna Mast 18alfa Communications 4 07-27-2010 11:01 PM
Supporting antenna mast jandg Communications 5 06-30-2009 01:52 AM
AMT Lightning 22 pistol Jester73 Pistol and Revolver Forum 0 04-10-2009 10:51 PM
Thunder & Lightning musiklover77 Disaster Preparedness General Discussion 40 04-06-2009 06:45 AM


All times are GMT -5. The time now is 12:44 AM.


Powered by vBulletin®
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright Kevin Felts 2006 - 2012,
Green theme by http://www.themesbydesign.net