Lightning LNB damage

[dwboston]

Major lightning activities in the past 6 hours and now I have two c-band dishes - both about 12 feet apart that are not apparently putting out any signal to our PowerVU receivers (using the AMC-1 and IS-9 (19) satellite). We have not yet started a check of the whole system, other than rebooting the receivers. We've inspected the dishes and LNBs and there is no physical sign of damage either at the dish or within 100 feet of the dishes, but can a nearby lightning strike create enough damage to destroy an LNB even if the lightning has not struck the dish?

Also, these are $400 broadcast quality LNBs. If they are damaged, are they trash now, or can they be repaired?

Thanks

GF

 

[Lassar]

Yes, near by lighting can damage you dish

Lighting can create a electromagnetic pulse that can damage the lnb. You coaxial cable pick up the pulse and transmit it to the lnb.

 

[FaT Air]

Test by replacing with a cheap LNB? It's nice to have backups

but can a nearby lightning strike create enough damage to destroy an LNB even if the lightning has not struck the dish?

I've had my hand in repairing the damage from many indirect strikes, only two direct strikes, over the years.

 

[mc6809e]

Last summer I had to repair/replace lnb's on 6 of my dishes after lightning struck a tree 75ft from the closest dish and about 125ft from the house. Had to use most of my spares and order replacements. BTW, the dishes are grounded and the coax goes through ground blocks. There was no pattern to the damage and distance from the strike didn't seem to matter. The dish closest to the strike lost the Ku on the C/Ku lnb. The next closest lost the C-band on the C/Ku. I also lost the entire C/Ku on a 6ft dish, two dishes lost one of the outputs on their Ku duals, and the dish furthest away from the strike, about 150ft, lost both outputs on the Ku dual. I had to replace two 8X1 and two 4X1 DiSEqC switches but here was no damage to any of the actuators or motors on the dishes and no damage to anything inside the house.

This was the second time I know of that lightning had struck that particular birch tree.

Ernie

 

[turbosat]

Sorry dwboston, but yes it can happen. I'd get a couple of run of the mill consumer c-band lnbs and swap them out. If that fixes the problem, then you can dig deep for those new, more stable ones! Best ground system in the world won't always outsmart the lightning. It is strange how the results play out-the worst storms I've had, that sounded like pure war, did no damage. But lightning several miles away from my house has blown out an lnb for me in the past. Thankfully, it IS rare. The damaged lnbs probably get junked, doubt that the components would be reliable even after repair.

 

[rv1pop]

I have had equipment burn out from static with no lightning; just hot, dry, strong winds. We could see the blue corona off the roof of the shed and it is Ufer(?) grounded. All the steel, roof and sides are bonded to the structural steel and the grounding re-bar in the foundation. Also bonded to the steel mesh in the slab.

Your mileage may vary!

 

[madmadworld]

Test by replacing with a cheap LNB? It's nice to have backups

#1 answer imo

 

[FaT Air]

You are correct. http://en.wikipedia.org/wiki/Ufer_ground
I've also heard of mixing copper or magnesium sulfate in with the backfill around a buried ground rod.
Some interesting reading on subject of grounding - http://www.swssec.com/grounding.html

 

[KE4EST]

I have seen all kinds of crazy stuff happen with lighting and dishes. I had one system that the LNBF was in pieces and coax burnt up but receiver was still fine or seemed to be.

 

[Anole]

Backup LNBs

#1 answer imo

Yea, if you shop around to be prepared for next time, ya might find new ones for $12, 15, 20 each, shipped.

 

[Lone Gunman]

Oh boy, do I have a good one for ya on this one!

I've got two systems. My Winegard system was installed by me at this new house back in July of 2000 and was moved from it's original install location from back in 1988 at my old house. NO GROUND ROD OR ANYTHING ELSE ON THAT SYSTEM AND NEVER A PROBLEM AT THE OLD HOUSE DURING THAT 12 YEAR TIME PERIOD. From July of 2000 to date at this new house that system has NEVER, EVER suffered a lightning related failure and it doesn't have a dedicated ground either! NO FAILURES ON THAT SYSTEM, even though I've actually left it on and watched TV during storms!

Then that SAMI system I have came along a couple of years ago and that's when my problems began. I mounted that dish right next to my new house about 50ft away from the Winegard dish and have had nothing but trouble with it since!! To date I've lost 4 (I think??, kinda lost track) LNBFs in one way or another, ie, some C, and others Ku and on one I just lost horizontal polarity on the Ku side. I've had two of my receivers HDMI inputs fried and it's gotten my 24" HD TV TWICE as well! The network switch that connected my AZBox Elite to my network has that one channel fried as is the the LAN part of that Elite. All from one strike. HDMI output on both that Elite and one of my Openbox S9s are also fried!

Last winter I installed a ground rod out by that SAMI dish and grounded it there to no avail as I just lost that Horizontal polarity of a DMX741s Ku LNBF side about a month ago during our first storm of the season. I did have one DMX that the Cband side was fried on though so I swapped out the Ku sides, ie, took two and made one good one.

So IMHO that ground rod was a waste of time and money as it's basically done nothing.

Here is something that's interesting though. I put an OTA antenna on my roof mounted on a 10ft mast back a few years ago. Ran a ground wire in through the roof vent and down into my HVAC room inside the house. I drilled a hole in the concrete floor in that room and installed an 8ft ground rod there for that antenna and haven't had any problems with TVs connected to that coax? Go figure!

I've just accepted the fact that the SAMI system is a lightning rod and I disconnect everything that's connected to it whenever a storm comes our way. That doesn't prevent damage to the LNBFs out on the dish though. OH and I've recently added some of those F connector type surge protectors to my receivers to maybe stop further damage there even though I usually disconnect the coax on that system during a storm.

I've talked to several "electricians" about this and all had different solutions, none of which come with any sort of assurance that the strike damage will stop??

 

[westom]

I've talked to several "electricians" about this and all had different solutions, none of which come with any sort of assurance that the strike damage will stop??

Your problems stem from not yet understanding relevant electrical concepts. For example, connect a 200 watt transmitter to a long wire antenna. Touch one part to feel no voltage. Touch another part of the same wire to be shocked by maybe over 100 volts. Why two completely different voltages on the same wire?

Well electricians are not taught anything that would explain it. Electricians are taught what must connect to what. And not why. Your problems also cannot be solved without learning why.

You have assumed earthing is a solution. Maybe. Or it can make damage easier. Understand why damage happens. In every case, a current enters something (ie LNB) on one path. Leaves on another. That current is simultaneous everywhere in the incoming and outgoing paths. Your ground may have only made electronics in the Sami dish the best (and destructive) path to earth. Your earth electrode must connect any incoming current to earth on a path that does not pass through the LNBF. Apparently you have instead made that LNBF the best current path to earth.

Normal is to have a dish struck, coax destroyed, and LNB unharmed. A connection to earth was via the coax - bypassing an LNB or receiver. Damage is always about a current with an incoming and another outgoing path.

Many (including electricians) assume a surge incoming means damage. If an outgoing path does not exist, then incoming surges do no damage. Every analysis must define both the incoming current path and the outgoing current to earth. Otherwise, nobody knows why damage happened.

Even that inline protector does not and cannot stop a surge. It is not suppose to. It only works when connected within feet of the single point earth ground. Protectors never do protection. Best protection is usually a wire to earth (no protector). Protector only makes that same connection when a wire cannot be connected directly to earth. Wire to earth is the better protection. A protector is the next best thing.

Too many (due to advertising, urban myths, hearsay, and wild speculation) assume a protector will stop or absorb a surge. No protector ever did that. Either a protector connects low impedance (within single digit feet) to what does protection (ie earth). Or a protector does nothing useful.

Remember that antenna with 100 volts and zero volts on the same wire? Electrical reasons also say why an in-line protector must be within feet of one important earth ground: single point earth ground.

 

[Cham]

Have had lightning damage here as well. Finding the path (as WesTom suggests) might indicate changes that can be made to mitigate future damages, but often there is little that can be done to further protect equipment other than adhereing to local electrical codes.

One suggestion though, grounding your satellite dish, having a grounding block for each conductor at the satellite dish located inside a metal weatherproof enclosure bonded to the same ground, and running the exposed cables in metal conduit (also bonded) as much as possible. Burying the cable between the dish and your house is also a great idea. Nothing will prevent damage from a direct lightning hit.

 

[northgeorgia]

Good analysis. I'm trying to understand all of this too, to get a better idea of compliance and protection. So the idea is to give the static build up, or in a worst case scenario, lightning, an electrical path of least resistance to a single ground -- which for many people would be the electric supply box ground on the outside wall of their home or inside where a metal cold water pipe just enters the home, right? What additional protection, if any, could be provided at the dish to encourage the dish/coax, rather than the lnb, to be used as the beginning point of the current? I have seen #8 aluminum or #10 copper are suggested gauges to use to connect the grounding block (within a few feet) of the ground. Is this usually sufficient?

 

[westom]

Nothing will prevent damage from a direct lightning hit.

Some may be in severe locations where all that additional work would be necessary. Because damage from direct lightning strikes is directly traceable to human failure. Routine is to have direct lightning strikes without damage. But only if an electrical current to earth is via non-destructive paths.

Generally you must have a ground at the dish. And a single point ground where all incoming coax wires enter the building. A service entrance that is also within feet of the single point earth ground. Coax cable must have earth grounds at both ends. A professional demonstrates this concept where even an underground wire must be earthed similar to exposed wires:
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

In the app note, a buried ground wire interconnects earthing electrodes to improve both grounds. In every case, a direct lightning strike is made irrelevant by how current goes to earth. Proper protection means nobody even knew a strike occurred.

Is 10 AWG wire sufficient? Well, 18 AWG wire (lamp cord) rated for 10 amps (and a maximum sustained current of about 60 amps) will conduct a surge current of up to 60,000 amps. A copper wire that is four times thicker (10 AWG) earths direct lightning strikes (typically 20,000 amps) harmlessly. The single point earth ground (typically 6 AWG) also easily conducts direct strikes to earth. However sharp wire bends, ground wire inside metallic conduit, ground wire adjacent to non-grounding wires, splices, etc compromises everything. Cold water pipe is often a least effective ground.

 

[Corrado]

I learned firsthand in July 2007 how destructive lightning is. In my case, I believe induced current from lightning that struck a tree near the buried ribbon cable passing by followed the actuator motor wires back into the house which were never grounded by design. It even ruined the digital KW/H utility meter and central AC compressor and all the AV equipment.

I have lost many LNBs over the past 25 years just from cloud to cloud lightning and always have spares. On a motorized dish, I normally point it lower if a strong storm is forecast and I'm not going to be home. Since I have practiced that and disconnecting the coax and actuator cables, I haven't lost anything.

 

[FaT Air]

"Remember a ground for lightning is very different from a DC ground or a ground for 60 cycles. Few electricians appreciate the difference." http://www.swssec.com/grounding.html
I haven't lost anything in years to lightning except for a tree in the yard. Power cords, coax, etc, get a one turn coil, ~6 inch dia., before attaching to electronics. I don't unplug anything. And many time are using it.
A former boss couldn't understand why, after many years of having lightning induced outages, at their tower sites, suddenly stop. There's still lightning??? Well, I "installed" a loop in the coax going to each transmitter.
FWIW: I won't take a shower during a lightning storm. Or use a wired telephone.

 

[Cham]

Wonder if cloud to cloud lightning (could be many miles away) within the apature of a satellite antenna could cause a failure due to signal overloading? The probe inside the LNB(F) would pick up a considerable broadband signal spike... In this situation grounding would have little affect.
I've only had one receiver go due to lightning, the corotor circuit was left ungrounded and thus was an efficient path from the feedhorn to the grounded power cord. The receiver still worked but wouldn't change polarity. That's when I tried my first LNBF..

 

[sergei]

To protect my receivers and dishes I've installed Holland Electronics Model SA-1F spike protectors on all my LNB's and LNBF's along with one at each receiver input. Price is around 8 dollars, but still cheap insurance in my book.

http://www.hollandelectronics.com/catalog/catalog.php?product_id=SA-1F-Spike Protection

 

[Cham]

Sergei, did you run a seperate ground at the receivers to connect to the spike protector? I only have one coaxial surge protector on a 160m long wire antenna. The antenna was hit once (same time my receiver got hit) and it blew up the feed point/balun which was grounded to the tower at the 50' level, but the surge protector was ok (radio was not connected at the time).
I would like to protect the motor and sensor leads for the dish actuator better. Does someone have any recommendations for such a device? I did wire a couple .2uF caps in a pi network at the sensor to try to bleed off static or stray RF but I doubt these would to much with lightning... Maybe some good RF chokes or MOVs?

This talk about lightning gets me thinking... great topic and it always interests me.