Lightning protection questions

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DylanMadigan

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I did some research and I found most of my answers but a couple (or i found more then one answer).

I'd like to put up a 50ft mast, which would be slightly higher than the trees, making it the tallest point on the property (though lightning seems to strike the field and cherry tree only). I got some heavy duty cable to run the mast to a dedicated ground (a couple 5ft grounding rods). The ground rods will be in wet sand as we are about 20ft from sea level. I also got an inline lightning protector for the LMR400 line.



Should the inline protector be placed under the antenna, on the duplexor, or should I actually add a connection where the wire enters the building and place it there?

Can the inline protector be hooked up to the same line as the line grounding the mast?

Is this actually going to be able to handle a direct hit or will this only protect it from nearby strikes?
 

buddrousa

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I always ground either at the tower or at the weather head where it enters the structure.
 

mmckenna

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Should the inline protector be placed under the antenna, on the duplexor, or should I actually add a connection where the wire enters the building and place it there?
Direct lightning strike isn't the only thing you need to be concerned about. Even nearby strikes can induce enough energy into your feed line to cause damage.
For this reason, it's standard practice to put the lightning protector where the coaxial cable enters the structure. After all, the structure (home) is what you are trying to protect.

Can the inline protector be hooked up to the same line as the line grounding the mast?
Yes, but you need to look at your grounding as an entire system.
The mast needs to be well grounded at the base. This is to give a direct path for lightning to ground. You want that energy to go straight down the mast to the ground.
Since your mast will likely be a little ways away from your home, and your protector should be mounted where the coax enters the home, you should ground the protector below that point. That should be a straight run of heavy copper cable straight down to the ground with a ground rod there. Again, you want a straight and short run for the energy to ground.

All the grounds need to be at a same potential, for this reason, the NEC says that all your grounds need to be bonded. This would mean that the ground rod(s) at the tower base need to be connected to the ground rod at the house electrical panel. The protector and it's ground needs to be bonded to this also.

The idea is you need to get the lightning strike, or any induced energy, into the ground as quickly as you can. You want to give it a direct path, and you need to make sure all the grounds are connected to make a ground system.

The other thing you need to do is ground the coax shield in a couple of places. Industry standard is to ground the coax shield to the mast near the antenna, then again at the bottom. If you were running a taller tower, you'd do this every 100 feet or so.

Is this actually going to be able to handle a direct hit or will this only protect it from nearby strikes?
Depends on how well everything works.

If you are using a DC grounded antenna that is well connected to the mast, your coax shield is grounded at the top and bottom of the mast, you have a good ground rod system, low resistance ground, a good protector that is properly grounded, then you may survive a strike. Broadcast towers are hit all the time and they don't get knocked off the air. Mountain top repeater sites git hit directly or suffer nearby hits frequently as well.

The trick is to make the ground path though your ground system more attractive than going through your radio.

Doesn't mean that some energy will make it to your radio. It happens.

Based on what you are saying about lightning strikes hitting nearby, and that you are putting up a mast taller than the trees, I think you run the risk of taking a hit.

That would suggest that it might be a real good idea to talk to a professional and see what they can do for you. Not getting it right could result in damage to your home. There are other steps you may need to take, like installing a lightning terminal above your antenna, a better network of ground rods under the mast, etc. They'll also have the equipment to test the soil resistance to determine exactly what you'll need.

Even making your mast lower than the trees will not necessarily protect you.

A good place to study this is by finding a copy online of Motorola R56. It's a well written document that covers system/site grounding.
 

prcguy

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As mmckenna mentioned, let the NEC be your guide and specifically NEC article 810 for grounding antennas. Here is a link that covers many facets of the subject with pretty pictures: https://www.seapac.org/documents/seminars/2013/2013-Kuhlman-Applying the NEC to Amateur Radio.pdf
prcguy

Direct lightning strike isn't the only thing you need to be concerned about. Even nearby strikes can induce enough energy into your feed line to cause damage.
For this reason, it's standard practice to put the lightning protector where the coaxial cable enters the structure. After all, the structure (home) is what you are trying to protect.



Yes, but you need to look at your grounding as an entire system.
The mast needs to be well grounded at the base. This is to give a direct path for lightning to ground. You want that energy to go straight down the mast to the ground.
Since your mast will likely be a little ways away from your home, and your protector should be mounted where the coax enters the home, you should ground the protector below that point. That should be a straight run of heavy copper cable straight down to the ground with a ground rod there. Again, you want a straight and short run for the energy to ground.

All the grounds need to be at a same potential, for this reason, the NEC says that all your grounds need to be bonded. This would mean that the ground rod(s) at the tower base need to be connected to the ground rod at the house electrical panel. The protector and it's ground needs to be bonded to this also.

The idea is you need to get the lightning strike, or any induced energy, into the ground as quickly as you can. You want to give it a direct path, and you need to make sure all the grounds are connected to make a ground system.

The other thing you need to do is ground the coax shield in a couple of places. Industry standard is to ground the coax shield to the mast near the antenna, then again at the bottom. If you were running a taller tower, you'd do this every 100 feet or so.



Depends on how well everything works.

If you are using a DC grounded antenna that is well connected to the mast, your coax shield is grounded at the top and bottom of the mast, you have a good ground rod system, low resistance ground, a good protector that is properly grounded, then you may survive a strike. Broadcast towers are hit all the time and they don't get knocked off the air. Mountain top repeater sites git hit directly or suffer nearby hits frequently as well.

The trick is to make the ground path though your ground system more attractive than going through your radio.

Doesn't mean that some energy will make it to your radio. It happens.

Based on what you are saying about lightning strikes hitting nearby, and that you are putting up a mast taller than the trees, I think you run the risk of taking a hit.

That would suggest that it might be a real good idea to talk to a professional and see what they can do for you. Not getting it right could result in damage to your home. There are other steps you may need to take, like installing a lightning terminal above your antenna, a better network of ground rods under the mast, etc. They'll also have the equipment to test the soil resistance to determine exactly what you'll need.

Even making your mast lower than the trees will not necessarily protect you.

A good place to study this is by finding a copy online of Motorola R56. It's a well written document that covers system/site grounding.
 

Rred

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Is your location covered by any building codes, or does your insurer have any requirements? You might find that a standard 8' grounding rod is needed, not just 5'. And that solid copper, not just the usual copper-plated steel, will last you longer and make a better ground. FWIW.

Grounding and ground protection at the tower, rather than at the premises entry, will also offer some protection to the cable run between them, so you might consider biting the bullet and doing both. But even better, make a habit to disconnect the cable at the premises entry, and connect IT directly to ground, whenever the station is not in use. If you make that a habit, it ensures that anytime bad weather creeps in overnight, any strike or surge can only go to ground. I think MFJ is even making some strips that can go in the bottom of a windowsill, with extra connections to do that. Easy enough to DIY on that, though.

Polyphaser, a top name in protection, also has extensive docs on their web site, and a top reputation in the broadcast industry.
 

lmrtek

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you want the mast heavily grounded

it WILL be hit by lightning

when that happens, you want the lowest possible impedance path to earth for the strike energy

so multiple 8 foot rods bonded to the mast using cad welded connections

you also need to make the feedline the HIGHEST possible impedance path to the house

you do this by putting several minimum bend radius loops at the bottom of the antenna

this slows the strike energy to keep more strike current on the mast instead of on the coax

then you mount a coax suppressor at the entry point of

you again make several tight loops in the coax AFTER the suppressor

this again will keep more strike energy in the suppressor and going to ground instead of into the house
 

prcguy

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That all sounds nice but in no way will protect his equipment or house from damage. All grounds, house and antenna/tower must be at the same potential and usually with a central star type ground arrangement. Its possible to build a lightning proof system, just not practical for home use.

I've posted several times this week that its nearly impossible to protect your hobby antenna and house from a direct lightning hit. You would have to rip out your existing AC power entry, bury a ground cable around your entire house, usually 500MCM size with many ground rods bonded to the buried cable, then build out your AC entry panels and antenna entry points from scratch and all bonded to the new buried ground system.

That's for starters and you would usually hire a company to come out and measure and inspect everything to certify its built to a certain standard that might survive a direct hit. Not going to happen for most people so why give partial advise that will not do the job?

Unless your willing to pay for or replace everything that gets blown up or damaged from a direct lightning hit after you make recommendations to someone on how to ground it, then I suggest you not suggest. In my opinion, if someone takes your advise and it bites them, then you own the problem.
prcguy


you want the mast heavily grounded

it WILL be hit by lightning

when that happens, you want the lowest possible impedance path to earth for the strike energy

so multiple 8 foot rods bonded to the mast using cad welded connections

you also need to make the feedline the HIGHEST possible impedance path to the house

you do this by putting several minimum bend radius loops at the bottom of the antenna

this slows the strike energy to keep more strike current on the mast instead of on the coax

then you mount a coax suppressor at the entry point of

you again make several tight loops in the coax AFTER the suppressor

this again will keep more strike energy in the suppressor and going to ground instead of into the house
 
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DylanMadigan

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Thank you for the advice everyone.

The antenna will be mounted to the side of a two story garage (well 1 story and attic). I got 4 5ft ground rods and can get more, each one I plan on running directly to the mast with its own cable, and the polyphaser cable to the 4 on the mast. I'll ground the outer layer of coax shielding at the top of the mast only as the mast is telescopic and the polyphaser will be in the wall just a foot of cable from the mast bottom.

As far as AC power, the UPS I have on it guarantees lightning protection for the equipment so I'd only have to worry about the UPS itself dying from a power line hit.
 

prcguy

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NEC says you have to bond all additional ground rods to your main AC service panel ground and your area will require a specific size and type ground rod. Does your whole house run from the UPS?

In a direct lightning hit one of the main things that blows up equipment is the difference in ground potential between the electrical grounds between the area that gets and your AC panel. It can be thousands of volts difference just on the grounds. A direct hit can destroy all the equipment that is plugged in at your house including all your TVs, radios, computers, you name it.

What you are considering doing is like packing for some extreme sheer cliff climbing and instead of all the usual ropes, safety and protection gear, you are packing a few band aids in case you fall 200ft onto the rocks below. You may not plan on falling but if you do you will not survive.

Its best to ground to NEC standards at the minimum and realize you can't ground your stuff on your own to survive a direct hit and deal with that by disconnecting your antenna during storms or when your away, etc. The worst thing that I can imagine is assuming your protected when you really are not and having very expensive or deadly consequences.
prcguy


Thank you for the advice everyone.

The antenna will be mounted to the side of a two story garage (well 1 story and attic). I got 4 5ft ground rods and can get more, each one I plan on running directly to the mast with its own cable, and the polyphaser cable to the 4 on the mast. I'll ground the outer layer of coax shielding at the top of the mast only as the mast is telescopic and the polyphaser will be in the wall just a foot of cable from the mast bottom.

As far as AC power, the UPS I have on it guarantees lightning protection for the equipment so I'd only have to worry about the UPS itself dying from a power line hit.
 

mmckenna

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As far as AC power, the UPS I have on it guarantees lightning protection for the equipment so I'd only have to worry about the UPS itself dying from a power line hit.
Your UPS will do nothing for you to protect against a lightning strike. What it will do is dump energy to ground if there is a nearby strike that gets into the power lines. Your UPS will probably be a smoldering mess and the 12-14 gauge ground wire in your home may no longer exist after said strike.

NEC is the rule you need to meet. Not the guarantee of the UPS manufacturer. Your homeowners insurance company will not protect you if you do not fully follow the NEC rules.
 

Rred

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" the polyphaser will be in the wall "
So you intend to bring lightning INSIDE THE PREMISES. I'm not sure that would be considered acceptable by any fire codes, electrical codes, or insurers. Even if it is "just a foot" lightning tends to do as it please, and like a vampire, one should never invite it inside. Put the polyphaser in a box, a metal box, OUTSIDE the house. A junction box also helps to keep water from following the cables into your walls, so you win two ways.

Let me tell you about a UPS. I had a fairly large Tripplite UPS on my computer years ago, in the middle of a large masonry-over-steel building. The kind that never take slightning damage aside from trees falling on it. The computer needed to be on 24x7 and one weekend I went away.

Came back after a weekend and found the computer was dead. Heck, the UPS was dead. WTF?

The *internal* fuses that Panasonic built into the AGM batteries were both blown, the battery cases warped and obviously heat damaged. There had been a nasty series of thunderstorms over the weekend, and I can only think the UPS failed to clamp a surge, and the batteries fortunately blew their fuses before they could have caught fire.

Tripplite were uninterested, they said if I cut off the power cord and sent it in, they'd give me a special deal on a new one. (Haven't bought one of their products since.)

So much for UPS guarantees. You'll see lots of fine print in them as well. And you'll still be left trying to re-order, re-configure, and restore the system, which can mean a solid week if you have lots of software to re-install and need to install and update the OS on a new computer as well. Your backups typically won't install on a different new system.

Don't invite the vampire in. "Garlic" is cheap.
 

KC4RAF

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+1 with other posters. There is NOTHING that will protect from a direct lightning strike. UPS isn't designed to protect from such hits. And the NEC has strict rules that must be followed for at most minimum protection. It calls for 8' ground rods, and they must ALL be tired together.
There are those who say that they get by with none or maybe one rod at the mast or tower and have never suffered damage. True. But they haven't been hit yet either.
BTW, you DON'T have to have a direct hit to get damaged. A near by strike does a world of hurt to plugged in equipment.
When lightning is close, I unplug all my equipment. But here's a nasty after tell; even unplugged, if the lightning is close enough, it still can cause damage!
 

mmckenna

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Thank you for the advice everyone.

The antenna will be mounted to the side of a two story garage (well 1 story and attic). I got 4 5ft ground rods and can get more, each one I plan on running directly to the mast with its own cable, and the polyphaser cable to the 4 on the mast. I'll ground the outer layer of coax shielding at the top of the mast only as the mast is telescopic and the polyphaser will be in the wall just a foot of cable from the mast bottom.

As far as AC power, the UPS I have on it guarantees lightning protection for the equipment so I'd only have to worry about the UPS itself dying from a power line hit.

Dylan,

You are missing a lot of what we said above.

5 foot ground rods are not sufficient. You need 8'.
Connecting each of the rods to the mast base is a good start, but you need to ring all the rods together. So, each rod connected to the mast, AND a separate heavy cable connecting each of the rods together. You absolutely need to have the potential equal between all the rods.
You need to ground the outer shield of the coax at the TOP and BOTTOM of the mast, not just the top. You want the energy to flow to the mast, not down the coax shield.
Since this is a telescopic mast, you need to bond each joint of the mast. You want the mast to take the energy to ground. In fact, I'd say run a large gauge copper cable from the top of the mast to the base.

And, absolutely, the PolyPhaser should be outside the house. Run a heave gauge copper wire straight down from the PolyPhaser to a dedicated ground rod. You want the down lead to be straight with no bends. At the ground rod, run a cabe to the rest of your ground network.

This stuff is really important. You are putting a big metal mast into the sky above all other in a lightning prone area. Might as well paint a big target on your roof. Cutting corners is going to be disastrous.
 

lmrtek

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I started using single point grounding at my towers in the 80s

LONG before the NEC or ANYBODY else was advising it but I guess to the newbies this is some new revelation

And I thought hams were the only ones that waste their lives trying to re invent the wheel
 

prcguy

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Who is reinventing the wheel? Why would single point grounding of your tower in the 80s have anything to do with the OP and his nearly impossible goal?

Do you have a lightning lab where you test survivability of direct lightning hits? Have you ever had a direct lightning hit and everything survived? I have at multiple sites, not counting the antenna itself getting blown apart.

Is the ham comment about me? I have an amateur license, but that has almost nothing to do with my limited lightning experience.

I will not tell someone on an Internet forum how to specifically protect their equipment from lightning or give instructions beyond what's stated in the NEC, that would be foolish and potentially costly for me or whoever gives the advice. I did that for my employer for many years and take full responsibility for any failures at those sites, which are none at this point

If I read lightning advice on this forum that I believe is not a good idea I will usually make a comment and I always point people to NEC article 810 for guidance. Got any problems with that?
prcguy

I started using single point grounding at my towers in the 80s

LONG before the NEC or ANYBODY else was advising it but I guess to the newbies this is some new revelation

And I thought hams were the only ones that waste their lives trying to re invent the wheel
 
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