Lightning protection

[VK4WDM]

I have capsule type in-line lightning arrestors in my feed lines but I don't totally trust them (should I?) and manually disconnect them when there is a storm in the area. This can entail going outside in the pouring rain and often dark - not good for a and it can happen several times a day during our wet season.

I am thinking of some sort of junction box where I could ground all antennas remotely. I know that there are electrical antenna switches that can do this but as far as I know they are only available for HF. I need something to handle VHF and UHF too.

Ideas anybody?

73

Wayne VK4WDM

[VK2HC]

Hi Wayne,
I use surge arrestor's on all external antennas to a stainless steel base plate within the window and one heavy duty 10mm earth cable from the base plate to ground rod outside the shack window, I view the use of surge arrestors as convenience only.
My job as a radio tech I get to see a lot of strange things in the field, I have seen a collinear antenna pealed back like a banana after a ( lightning hit ) and the repeater still happily working, a direct hit would have vaporised the collinear antenna, the surge arrestor will discharge 90 Volts and above( with in limits) to ground what happens to below 90 volts ??.
Like you I have reservations in regard to lightning and a direct hit will take out everything in the shack, as everything is ( or should be bonded to ground AC, DC and RF ) lightning can use this path on it's way to ground, during thunder storms I stay out of the shack. I do not try to uncouple antennas during a storm, I try not to worry too much during a storm and treat lightning with the greatest respect, I can always replace radios and live to enjoy amateur radio to a ripe old age.
Regards to all and best wishes.
Peter VK2HC.

[VK4WDM]

I should have given a better description of my present setup.

The arrestors are mounted by their grounding lugs to a 5mm thick brass plate mounted on the outside concrete block wall of the shack. There is 15mm diameter power cable from the brass plate to a 3m long ground rod that has a gal pipe with holes alongside it so that water can be put down to keep the area around the rod moist. The base of the antenna mast is also grounded via the same type of cable to the same ground rod.

I guess the major question is: do I really need to disconnect the lines when there is a storm or can I rely on the grounding to do the job?

Yes I am a bit paranoid, I saw first hand what a strike can do on a RAAF comms station a few years back and it was supposed to have commercial spec protection

73

Wayne VK4WDM

[VK4TI]

Disconnect and ground , or you may suffer a high level epl or thousand of amps and volts

[VK2GFC]

Hi Wayne,
I guess the question is what you expect the arrestor's to do, I agree with Peter, a direct hit will do an amazing amount of damage. Have seen this in a previous job.
a meter of 4 inch coax vapourised....oops, we replace the coax cable all 700m of it. ( yes 4inch diameter )
The wall plate will put a good earth on the coax, this should allow the antenna to help discharged the air around the antenna its reducing the chance of a "streamer" and then a full strike.
At the broadcast sites the coax outer is bonded at the building entry and the middle of the run and the top to the mast. If you can bond the coax outer at the shack to a good earth
then you are doing as much as is practable. Bonding the inner to earth will not help too much and getting a switch to do this would be another point of failure.
Disconnect the coax at the shack end is good, that's my approach, so far so good. What happens to the 90V of charge after the arrestor, is the front end of the radio has to deal with it.
Just replaced two 27MHz radios at the local Marine Rescue, they did not survive the storm, the vhf radios did. They had surge arrestors fitted.

You could have an earth plate with some PL259 sockets on it in the shack and plug all the cable in there during a storm, save going outside.
Hope that helps, it is a real thorny issue and you can only do what you can, at least you are doing something.
All the Best
Gordon VK2GFC

[VK5TM]

RAAF comms

and

commercial spec protection

, well there's your problem, it should have been 'military spec protection'

Unfortunately, there are many sides to and debates about lightning protection, so there is a lot of bulldust mixed in with good stuff.

Without spending mega dollars, you aren't going to get any where near the protection that broadcast stations have, However, provided the surge protectors haven't degraded, a 5mm brass plate and 15mm (hopefully stranded, not solid core) cable to the ground rod should provide a reasonable level of protection against anything but a direct strike.

If you are uncertain about any of your lightning protection measures, the oldest adage of " If you don't want lightning in your shack, don't "lead" it in" is still the best one. I.e. disconnect all cables that could conduct lightning into the shack.

[VK4WTN]

hi Wayne, always a problem to know what to do about lightening protection. A local ham up here lost nearly all his gear to lightening two years ago. He did all the right things disconnected the antennas and all the 240V plugs and left his ground buss connected to the radios but the lightening was able to totally destroy all his radios via the ground connection.
The only safe way is to disconnect everything from the radios, antennas power and ground.
regards Wayne VK4WTN

[VK2GFC]

Hi Wayne, see if you can find this document on the web.

try this link www.bwcelectronics.com/articles/WP30A190.pdf
Its a good article written for radio amateurs.
Some good info in it.
Regards
Gordon
VK2GFC

[VK6ZFG]

The function of surge diverters in antenna systems is not always fully understood.

In a proper installation the outer of the coax feeder should be earthed at the top and at the base of the mast and if a long run preferably periodically along the mast as well. The mast in turn should be connected to a low impedance earthing system at the base (especially so if the site has a metallic connection of any type (eg; cable, pipes) to a remote earth).

Why are antenna surge diverters used?

The function of a surge diverter at the base of the mast is to minimise the voltage difference between the inner and outer conductors of the coax at the location of the surge diverter. This is all it does. The lightning energy present still needs to be dissipated somewhere.

During a lightning strike a voltage potential develops between the top of the mast (where the antenna is located ) and the base of the mast due to the very high currents flowing.

A simple example is a side mount dipole. Here, the centre conductor of the coax connects through the dipole to the mast. The centre conductor of the coax at the base of the mast is thus connected to the top of the mast. It will as a result have the voltage difference between the top and bottom of the mast.

The surge diverter prevents the voltage difference between the top and bottom of the mast from at the equipment antenna input (centre pin to ground). That is all it does. The lightning energy is still there to do damage. This can be avoided or at least minimised through a good low impedance earthing system and short heavy bonding conductors.

Lightning protection is in a way like insurance. I does not guarantee it will not happen but at least if it does it will be less painful. Disconnection serves to increase the insurance.

[VK6ZFG]

Basic Arrangement

[VK2EM]

It's also a good idea to disconnect your telephone line before a storm, because lightning can enter the shack from the telephone line, to a modem, computer, and then, into radios!
Telephone lines are essentially balanced... 'twisted pair'... and there are many places that the line can collect lightning impulses (cable pits, connection boxes, etc).
A lot of todays electronics are NOT earthed...(modems, PVR's, Set Top Boxes, etc) by virtue of their construction with switch mode power supplies, and only two wire (no earth) power leads!
So once lightning is in your house, it is free to run around looking for a 'low impedance' earth!
Having worked in the communications industry since 1962, I have seen numerous instances of electronic equipment being destroyed by lightning strikes via the telephone line (also power lines AND/OR TV antenna cables for that matter!)

73... Bruce

[VK2DVZ]

yep, during recent storm events - not sure which one, i lost an extension monitor with internal power supply that i use with the laptop at times. it was plugged into the 240v power board only that also had the elevation actuator plugged into at same time. actuator OK, monitor throw away job. all coaxes and power leads were unplugged at that time.....so disconnect all rotators/elevation actuator leads also - mine weren't ...disconnect everything. not the first time i've had gear destroyed.

[VK5PJ]

Hello Wayne,
in one of the first Gipps Tech conferences I attended, Guy, vk2ku gave a presentation on what had happened at his QTH with a then recent lightning strike that caused a heap of damage. If possible I would recommend getting in touch with him for a copy of his presentation, it was a gem.

The one thing that stuck in my head from that presentation and some thing that Guy emphasised a number of times, was the importance of a good low resistance connection between the tower and the shack earth (not via the coax or control cables) to ensure they stay at a similar potential difference, should a ground strike happen near you.

Most of his damage resulted from ground currents that took out some un expected equipment in the shack and house.

Regards,

[VK4TI]

All good advice being the difference between a normal electrical ground (300 ohms) and a communications geound( <3 ohms) you can never have to many ground spikes

[VK4WDM]

Hello Everyone

I started this thread not so much for my own edification (although I have learned a lot so far) but like a lot of my threads, to get a discussion going on a very important aspects of our hobby and drawing on the professional expertise we have in our ranks. To my mind that is an essential function of a forum like this: to educate the new hams, and to re-educate and remind the more experienced ones.

The info in the link provided by Gordon VK2GFC is really good: http://www.bwcelectronics.com/articles/WP30A190.pdf

Something I have seen in my reading is that copper strap, like that used in automobiles, is recommended, others say that HD stranded wire is preferable. What say you?

73

Wayne VK4WDM

[VK1JA]

Hi Wayne,

Not a direct answer to your question, but for reference sake, about 5 years ago now a tree out the front of a house 5 doors away (same street as my QTH) took a direct hit by lightning. I drove past the house on my way home from work that afternoon not knowing that what had happened and I saw the owner of the house sweeping up what seemed to be thousands and thousands of match sticks off of the road.... I stopped and asked if he was ok and asked what had happened, he said the match sticks were what was left of the 10 meter tall gum tree after a lightning strike !!!

He said luckily no one was home at the time, but every electrical appliance that was plugged into a socket of any kind in the home (power, telephone, foxtel, data) had blowen up. Regardless if it was on or not - every single appliance in the home was dead !!

From that I took away that there is no way you can stop so much power, even if you construct the best earthing system you could still end up blowing appliances (radios etc). It's the risk we take, but we can minimize the risk as much as we can.

If I see a storm coming close by I disconnect anything that I want to save, and when I say disconnect I mean isolate totally, no cables (power, coax, data, phone) are left connected to the appliances that I want to save. Remember that if you get a hit you will suffer some sort of damage, hence 99% of the time you will end up putting in an insurance claim. But the key here is to save the critical items.

Of course we can't predict the rogue lightning strike or if we're at work we can't rush home everytime it looks like a storm is coming, if only there was a way we could harness the power of a lightning strike

[VK6ZFG]

Hi Wayne

Most of the energy in a lightning pulse is at around 100kHz and while this is a high frequency relative to the mains frequency, it is not in RF terms. Many of the comments made on lightning tend to overlook this.

Conductor/cable type is not all that important. What is, is having sufficient cross sectional area to be able to handle the very high current pulse. This depends on the material used eg: copper or steel etc as this determines how high the temperature of the conductor can get before it melts. If the cross sectional area is inadequate, it will act like a fuse!

The conductor must also be suitably physically restrained as a considerable force will be generated while the current flows through it.

Equi-potential bonding is also important to to ensure the touch voltage between different items remains at a safe level. Ground mats are often used to ensure this occurs (eg: at the base of towers).

[VK2XSO]

Unfortunately, there are many sides to and debates about lightning protection, so there is a lot of bulldust mixed in with good stuff.

Yes, that's true and you can see some of it creeping into this thread.

Lightning arresters will do their job. But they are not a lot different to a fuse.
A fuse will protect part of a circuit in particular circumstances, but not do so in others.
Wearing a seat belt in a car increases your chances of surviving a crash, if does not guarantee your survival.

.... disconnect all cables that could conduct lightning into the shack.

Disconnecting everything is a fairly good way to ensure the best chance of equipment survival.

.....left his ground buss connected to the radios but the lightening was able to totally destroy all his radios via the ground connection.
The only safe way is to disconnect everything from the radios, antennas power and ground.
regards Wayne VK4WTN

This wins my award for myth of the day. I might suspect that somebody has coloured up this story isn't telling any truth.
Starting with an indication of a poor earthing system. Possibly with an earth loop of some kind.
For "all" of the equipment to be destroyed, also seems very unlikely. Even site where I've seen a direct hit to equipment, the damage is localised and in a lot of cases other equipment in close proximity continues work without an issue. Think of the chassis of a radio as a farraday cage. Either somebody is telling you the laws of physics don't apply to them, or there are some exceptional circumstances they are not telling you about, either deliberately or because they are not aware of them. This often comes in the form of accusations against a deity.

And it's easy to think carefully about if this is true or not by doing a simple thought experiment.
Ask ourselves how to deliberately damage a radio with a lightning strike without connecting anything but an earth wire.
I think you'll find it requires a direct strike to a part of the radio that isn't the chassis and has a different earth at a different potential close by.

"Correct" earthing (not ham radio standards) is a very important part of protecting against lightning damage.
An Earth mat short of a farraday cage offers the best protection.

EQUIPOTENTIAL BONDING. If everything in the shack is at the same potential then no damage will occur.
(In this forum you will obey ohms law.)

In reality it's impossible to have zero ohms to everything inside the equipotential boundary. So again it doesn't prevent against catastrophic conditions but it certainly does offer very good protection.

Depower equipment
Disconnect antennas.
Disconnect external cables like rotator control cables.
Disconnect cables to power supplies like 240V plugs.
Do not disconnect your earth wires. (Unless you have a poor earthing system in which case I wonder why you bother earthing anything in the first place)
Do not leave cables, microphones etc lying in close proximity to earth other.

Of course if your antenna is hit, it's going to come down the coax, jump the insulation to the microphone and find it's way to earth ruining your day in the process.
But, if your tower was earthed, and your radio was bonded to the same earth as the tower, then your radio and the tower will be at the same potential when the strike occurs.
The potential from the coax to the microphone will be minimal and damage will most likely not occur provided there isn't a better earth somewhere else close by.
Which begs the question again. Why is your earth not as good as that one and why didn't you bond to it ?

[VK4WDM]

But, if your tower was earthed, and your radio was bonded to the same earth as the tower, then your radio and the tower will be at the same potential when the strike occurs.

I my case this is easy as my antenna mast is just outside the shack wall and the tower and the equipment both share the same grounding rod, but what say the tower was 25m away from the shack how can you ensure that the radio and the tower are bonded to the same earth then?

73

Wayne VK4WDM

[VK4TI]

I my case this is easy as my antenna mast is just outside the shack wall and the tower and the equipment both share the same grounding rod, but what say the tower was 25m away from the shack how can you ensure that the radio and the tower are bonded to the same earth then?

73

Wayne VK4WDM[/quote]you connect the spikes at each end to the spike in the middle with a suitable cable . which all connects to your several grounds near the shake achieving low ohms reading and low epr