Antenna vs Lightning?

[pseconds]

I know all about the therories of lightning, but not sure how lightning works in real life. For example, here's my setup:

My discone antenna is attached to my roof and is the highest point of the house. The antenna and 9ft mast area attached by heavy copper wire to a grounding rod 2 stories down. RG-8 cable runs 50 feet through my attic and comes down into my office on my desk. My scanner is plugged directly into the antenna.

My qustion is, if the antenna gets hit by lightning, what will most likely happen? Besides blowing up my radio, am I going to get electrocuted if I'm sitting next to it? Will it likely start a fire if papers and stuff are nearby? Would a fire start in the attic along the feedline? Will it fry the computer which sits under the desk?

Just curious what things could happen. Thoughts & theories?

 

[hoser147]

About anything can happen. Alot of members on here disconnect the coax and put in in a glass jar. Hopefully it will just follow your ground and thats the best possible outcome. I have seen many lightning strikes after the fact. Some fryin electrical items in the structure due to surge, and others have burnt to the ground. Others it blew drywall off the wall due to following the thin metal strips used on the corners of the walls. Im sure there are others who have seen other things caused by a strike. Keep your fingers crossed Good Scannin Hoser147

 

[prcguy]

All of the things you mention could easily happen including burning down your house and killing someone using the radio. Some of the current from a direct hit will dissipate into the ground via your ground rod but lots of current will also flow to anything else the coax is connected to or is close to. Look at the diameter of your coax braid and compare it to the ground wire you used. The coax is probably 10 times larger than your ground wire and looks much more appetizing to massive current. It takes an expert to design an antenna system that will take a direct hit and survive and the building electrical is usually designed at the same time with lightning in mind. Towers or masts will have multiple ground rods and cables are usually cad welded to the ground rods and tower with no sharp bends. The building perimeter will usually have a ground ring of 500 MCM copper cable (about ¾” dia) with multiple ground rods along its length and the building electrical will also be tied to the ground ring to help keep everything near the same potential during a strike. Cable entry points will be through a metal panel with lightning arrestors and the panel will be bonded to the ground ring. Anything less than a professionally designed and built system may give you a false sense of security, which is worse than no protection at all. I’ve worked at many mountain top repeater sites and microwave broadcast facilities that are built similar to what I described and some of the sites take direct hits every year with no damage. The glass jar trick may contain the arching across your connector from static buildup, but a lightning bolt is not going to be persuaded to stay inside the jar after traveling several miles through the air.
prcguy

 

[ka3jjz]

Your ground wire is how long??? At that length, and with only a single ground rod, it's probably not very efficient.

This article (from our wiki) is somewhat technical, but it's a must read on the subject...

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

73s Mike

 

[kb2vxa]

"A lot of members on here disconnect the coax and put in in a glass jar."

Yeah, the same ones who wear tin foil hats. The mast is properly grounded but don't take the chance lightning won't take the coax route to ground too, just leave it disconnected from the equipment when not in use and hope for the best. That's right, don't let a storm sneak up on you when you're away or asleep.

I'm not too keen on trusting wired connections to the outside world either, lightning has been known to enter via power and phone lines even when utilities are buried. They present a better ground than ground and get hit more often than above ground lines. Don't be like Buster (Myth Busters) and get fried, trust nothing and disconnect everything when a storm is in the area.

 

[Bucko]

The purpose of putting the coax in the jar? Are you going to let the coax lay on the floor when disconnected from the radio? Maybe you have not seen mother nature roll off your Coax? I agree grounding is important part and disconnecting for a storm is a very wise move and have done so for many years.

 

[Raccon]

I know all about the therories of lightning, but not sure how lightning works in real life. For example, here's my setup:

My discone antenna is attached to my roof and is the highest point of the house. The antenna and 9ft mast area attached by heavy copper wire to a grounding rod 2 stories down. RG-8 cable runs 50 feet through my attic and comes down into my office on my desk. My scanner is plugged directly into the antenna.

To improve things you could install a surge arrestor into the antenna line, preferrably a bulk-head mount that is grounded outside of the building, by connecting it to the existing rod. Use a metal plate for the cable entry and ground that, too.

My qustion is, if the antenna gets hit by lightning, what will most likely happen? Besides blowing up my radio, am I going to get electrocuted if I'm sitting next to it? Will it likely start a fire if papers and stuff are nearby? Would a fire start in the attic along the feedline? Will it fry the computer which sits under the desk?

Just curious what things could happen. Thoughts & theories?

Any of those things could happen. What exactly happens depends on how much current will go through the antenna cable and if the lightning flashes over to another conductor.
The strike may also induce harmful currents into your power and possibly telephone lines (if they are close), thus it could damage virtually any electrical equipment in the house, not to mention any fire that could be started.

As kb2vxa says you should also consider to protect the incoming AC mains supply and communication lines, a lightning doesn't need to directly strike your antenna or other parts of the house at all, it can also do a lot of damage by hitting anywhere nearby.

 

[iMONITOR]

Your biggest concern will be the possibility of getting killed, or having your house burn down.

The purpose of the ground is primarily to prevent the lightning strike from happening to begin with. If it does strike, the ground will do very little to protect anything.

 

[gcgrotz]

Not to argue but...

I've never seen a ground ring with 500mcm copper. Yes, it is used as the main ground bar connection in buildings but the ring is always constructed of #2 solid copper and all connections cadwelded. I wouldn't want to bury insulated stranded wire.

Just 2 weeks ago I had a cell site get hit, you can always tell a hit from a nearby strike that may blow out one circuit. I had 3 out of 4 T1 channels in a microwave blown, 2 surge protectors were blown out and 2 CSUs (T1 interface card) blown up. No RF damage to anything inside the building, usually the most damage is to circuits that enter/leave a building.

The bottom line is that if you take a direct hit, all bets are off and any or all of the possibilities mentioned might occur. Just be prepared as best as you can.

 

[prcguy]

The building I currently work in is about 225ft X 125ft and the original dwgs show 75, 8ft ground rods around its perimeter bonded to the 500 MCM ground ring 4ft underground. There are also lots of big antennas with air terminals bonded with 500 MCM cable. Every antenna structure has its own ground ring of 500 MCM bonded to the building ground ring and dozens of more ground rods for each antenna. This is in an area of very low lightning activity and I don’t believe this building has ever been hit to test the system. I’m not a lightning designer but 500 MCM seems to be the conductor size used for all main ground use in professional installations here.
prcguy

Not to argue but...

I've never seen a ground ring with 500mcm copper. Yes, it is used as the main ground bar connection in buildings but the ring is always constructed of #2 solid copper and all connections cadwelded. I wouldn't want to bury insulated stranded wire.

Just 2 weeks ago I had a cell site get hit, you can always tell a hit from a nearby strike that may blow out one circuit. I had 3 out of 4 T1 channels in a microwave blown, 2 surge protectors were blown out and 2 CSUs (T1 interface card) blown up. No RF damage to anything inside the building, usually the most damage is to circuits that enter/leave a building.

The bottom line is that if you take a direct hit, all bets are off and any or all of the possibilities mentioned might occur. Just be prepared as best as you can.

 

[SLWilson]

Lightning will win...

I know all about the therories of lightning, but not sure how lightning works in real life. For example, here's my setup:

My discone antenna is attached to my roof and is the highest point of the house. The antenna and 9ft mast area attached by heavy copper wire to a grounding rod 2 stories down. RG-8 cable runs 50 feet through my attic and comes down into my office on my desk. My scanner is plugged directly into the antenna.

My qustion is, if the antenna gets hit by lightning, what will most likely happen? Besides blowing up my radio, am I going to get electrocuted if I'm sitting next to it? Will it likely start a fire if papers and stuff are nearby? Would a fire start in the attic along the feedline? Will it fry the computer which sits under the desk?

Just curious what things could happen. Thoughts & theories?

The lightning will win. Simple. No question about it....

At one of our tower sites we took a "close" lightning hit here a couple of weeks ago. By "close" I mean we're not sure where it struck, it DIDN'T come in through the antenna system (tower / antenna strike) but here's what was fried.....

The telephone curcuits connected to the equipment (continued to work OK) cooked the line driver cards that control our transmit/receive on TWO base stations.

The surge protectors on THREE devices (two radios and one charger system) blew up. I mean completely BLEW UP!

Two AC breakers blew. Didn't burn them up, they just had to be reset.

We have polyphasers on all of our coax connections that are properly grounded. Didn't hurt them any.....That's why we know it wasn't a tower / antenna strike....

Our tower site generator is in a different building. It blew the fuses in the timer for it....

We had around $4,800.oo in parts and labor to repair all that was damaged in the "strike" at the site.

Best thing you can do is follow proper accepted installation procedures, put in the lightning arrester on the coax and ground it and hope for the best...

One last thing. This site has been there for ten years. It is on one of the highest points in our county. It's a 100 foot tower with a top mounted 22 foot tall fiberglass antenna (there are several antennas, but the fiberglass one is on top) and this is our first "lightning" damage in all that time We have had wind damage, but, this was out 1st lightning situation....

Steve/Gallia

 

[grem467]

The site pictured does not incorporate alot of principles of R56 (probably due to its age)

i can tell you from experience that a properly designed system following R56 WILL take multiple strikes with very minimal damage, if at all. Very seldom do we have an issue with lightning other than clearing MOSCAD alarms notifying us that we had strikes at the sites.

 

[Raccon]

The telephone curcuits connected to the equipment (continued to work OK) cooked the line driver cards that control our transmit/receive on TWO base stations.

Just curious - were the lines protected? If yes, how?

 

[kb2vxa]

This topic has been talked to death and still so few of you get the point. All you can do in the home is follow the NEC and hope for the best, you're not operating a communications or broadcast facility. I have seen the worst installations survive and the best suffer extensive damage, lightning IS capricious.

Bucko, are you being sarcastic or what? Don't answer, not likely I'll be back to argue anybody but I want you to think about it.

"The purpose of putting the coax in the jar?"

It's totally without purpose or any kind of reason.

"Are you going to let the coax lay on the floor when disconnected from the radio?"

I and others always do and why not? The whole point is interrupting an easy path to ground through the equipment and house wiring. That leaves but one easy path, through the grounding system. While nothing is perfect why provide TWO easy paths?

"Maybe you have not seen mother nature roll off your Coax?"

No maybe about it. Once upon a time lightning missed several much taller nearby antennas and trees and struck an 18' ground mounted antenna in my back yard. It followed the buried coax into the shack, arced about a foot to the ground bus, blew the PL-259 off and left a burn mark on the wall. Like I said, lightning is capricious.

 

[SLWilson]

Phone Lines

Just curious - were the lines protected? If yes, how?

Yes, the lines were protected/fused. I can't recall the name of the device, but, in the demark box, the telco had each circuit fused. It didn't blow them.

Plus, our radio tech had something installed between the phone company side and our equipment....Again, THEY didn't blow....

Like I said, with lightning, you just never know. Just keep your insurance premium paid up!!!

Steve

 

[oceans777]

Agreed - Using a discone on the roof awhile back I had a ground kit on my LMR400 into a 1 inch dia, 6-foot deep copper ground rod and my dearly beloved first Icom IC-R8500 and an HF wire grounded to a second rod using four feet of ground braid.

Lightning hit the discone while I was away and fried the Icom, the laptop nearby and a bizarre selection of switches, plugs and other electronics.

Lightning goes where it wants and may or may not stop to snicker at your best efforts otherwise on the way. I still ground where I can and hope next time it turns right instead.
But now I spend more of my time and $ making sure my insurance policy covers the equipment than I do on ground rods.

 

[SLWilson]

Insurance...

Agreed - Using a discone on the roof awhile back I had a ground kit on my LMR400 into a 1 inch dia, 6-foot deep copper ground rod and my dearly beloved first Icom IC-R8500 and an HF wire grounded to a second rod using four feet of ground braid.

Lightning hit the discone while I was away and fried the Icom, the laptop nearby and a bizarre selection of switches, plugs and other electronics.

Lightning goes where it wants and may or may not stop to snicker at your best efforts otherwise on the way. I still ground where I can and hope next time it turns right instead.
But now I spend more of my time and $ making sure my insurance policy covers the equipment than I do on ground rods.

PLUS, your insurance company "may" want to see your grounding system if you do have to file a claim, so, you HAVE to do it right, even knowing it "might not" help after all...

Our company sent an adjuster to check our grounding system and surge protection out after our last strike....

Steve/Gallia

 

[rfradioconsult]

Final Score

Lightning 10, Antenna 0, Radios 0.

Note: keep homeowners insurance up-to-date.

 

[Audiodave1]

Just chiming in here on the subject since I have a similar discone run length and location (And 4 other Yagi's).

For my station I followed the wiki link's suggestions to the best of my budget and as it COULD apply to my setup. (Much $$$$ to Ebay for copper and terminal blocks)

There's no way all of my equipment could survive a direct strike (or one within a reasonable radius of my energy collecting devices on the ends of coax) but I am somewhat protected from induced energy from a nearby strike as the ground potential of all components remains very similar. The only way I know I could survive a direct wold be to completely disconnect the tower and have the ends far enough away that they could not arc to ground.

My fulltime job has me designing speaker systems for outdoor locations. Anything from speakers on fences at NASCAR tracks, to speakers on light poles and scoreboards of high school fields to speakers distributed every 40' in stadiums. All of these are connected to amplifiers via a long interconnect which acts as a huge antenna for induced voltages. I see more damage from nearby strikes that direct ones. I hear about 3-4 direct strikes on our gear a year (with 2000 or so installations worldwide) that breaks most everything in the system. The induced voltage from most nearby strikes will break the speaker and possibly the amplifier.

I recommend to my customers that the only simple way to protect yourself is to not provide a path to ground for energy, either induced or directly applied.

Disconnect the power and feed lines when the system is not operating.

Dave