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post #1 of 7 Old 05-25-2007, 08:47 AM - Thread Starter
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This is a rant, so bear with me.

First, let me start by saying I should have KNOWN better. I am a broadcast engineer and deal with high RF environments, complicated studio setups, ground loops, and ESPECIALLY grounding/shielding techniques. It is this last thing that I am getting sick of.

Bought my house in 03. Here is backwater TN, they are not as "technically" inclined as one would hope. My home didn't come with any networking, or cable runs other than the typical single cheap RG6 run and phone jack in all the rooms.

I spent a great deal of time and effort wiring up my home with multiple ethernet jacks in every room (except bathrooms and kitchen, LOL).

The root of the problem is everytime we have a storm, something in my house gets blown up. To date I have lost:

2 satellite receivers
1 multiswitch
3 PCs (network cards blown to hell)
2 network switches (same switch popped twice)
and a Xbox twice.

Fortunately, my living room "HT" setup has not suffered any damage (knock on wood) as there are some pretty long runs in wall between the equipment rack and TV, but nowhere near as long as my CAT5e runs.

Yes, i have surge supressors in all rooms with all gear. Nothing fancy, just the "monster" brand MOV variety. However, in my experience, surge suppressors don't ELIMINATE the possibilities of lighting damage, they just REDUCE the likelyhood of damage with strikes.

Where I work we have a 300 ft lighting rod (radio tower) out back, and although we do suffer damage occasionally, its nowhere near the extent I do a home.

Now, the satellite receivers/multiswitch I don't *think* I can do anything about; think those were a fluke. In my mind the root of the problem is my PC network.

In every case above, i am conviced the long cable runs "picked up" the energy from a nearby strike, creating a massive current flow in the cables themselves, wiping out equipment at the ends of the cables. I do not believe power line induced surges are a problem at my house.

Lightning is a funny thing, but understanding what causes damage from storms isn't as complicated as one would seem. Its pretty easy to understand actually. Dealing with it, is also not too complicated as well.

Basically, anyone with a BEE background understands that if you have a conductor, and you run current through that conductor, it will generate a magetic field at right angles to the current flow. Conversely, if you take a magenetic field and run it through a conductor, it will generate a current flow. This is the basics of how a motor or generator works.

Now, a lightning strike introduces a MASSIVE amount of current. Also, at the same time a MASSIVE magenetic field is created. As that magnetic field travels it will induce current flow in any nearby conductors (as in, my network cat5). Such massive current flow induced into the conductors will cause the associated voltage drop on the devices at the ends of the conductors, and usually that voltage drop is substantially higher than the operating voltage of the equipment, and as a result, the "magic smoke" gets let out.

A real good example of this phenomenon happend to us years ago. We took a *direct* massive lightning stike on our tower out back. Although we suffered no damage at the time, every CRT monitor in all 3 buildings in our premises turned all sorts of different colors; as if a magnet had been run accross the screen. (Fortuneatly, we had a "bulk eraser" designed for erasing magetic tape that fixed them all-in effect acting as a"degausing coil").

Now, there is some good news. The energy generated by a lightning strike behaves logrythmicly, not linearly. What that means is, if you double your distance from the strike, the amount of energy that would be "picked up" would go down 10 fold. Very similar to the way that amplifier power and perceived loudness works (if you have a real 100watt amplifier and want to "double" the loudness to a given speaker, you need to increase the power to 1000watts).

So, the further you are away from the strike, the better off you are. And since the energy decreases rapidly with distance, you don't have to be too terribly far from it to be okay.

The problem is, where I live, I have crap all around me that lightning loves to hit. Neighbors put up flag poles (while a patriotic gesture, this has caused me more grief than anything else, as I have witnessed direct strikes to them, and the associated damage along with it), and rather large trees in the far back of my property.

This is the first house I have had this problem with (and coincidently, my very first home purchase....grrrrr).

So, basically, you either live in an area prone to nearby damaging strikes, or you don't. I fall in the former category.

So, what can be done to minimize the potential for damage you might wonder...Three things:

1) Surge suppression
2) Shielding
3) Proper grounding

Lighting can easily be induced into power lines, phone lines, cable, or any other conductors coming into the home. The longer the conductor, the "better" of an antenna it is for picking up energy from lightning.

So, the first place to start is surge suppression. I won't go into it, just suffice it to say that I am not one to spend large amounts of cash, so I have inexpensive suppression. But obviously, different types of suppression are better than others, and *generally* you get what you pay for. However, in my opinion, NO suppressor can ELMINIATE the potential for lightning damage, only reduce the likelyhood for it.

They sell whole house suppressors (very good invenstment IMHO if you can afford it)-its what we use at work.
Then you have the plug strips with suppression (I have this type). They also sell coax cable surge suppressors, which I have in my HT setup only. I do not know if S-video protectors are available, or if coax type suppressors are suitable for component video use or not.

Although they *do* make and sell surge suppressors for ethernet networks, they are *TERRIBLY* expensive.

The problem is that although you may have perfect surge suppression on your ac line and phone, if you have really long cable runs, ac line protection only isn't going to help.

So, that brings us to the 2nd line of defense-Shielding; Something that is not really considered too much in the home environment, and this is exactly where I went wrong. If you could "shield" the signal carrying conductors inside a cable, and "drain" off any induced energy to ground than that would really help protect the equipment located at the ends of the cables. Fortunately, they DO SELL shielded cat 5/e cable.

Which brings us to the last, yet IMHO MOST important thing you can do to help reduce the likelyhood of damage, and that is proper grounding.

I say it is the most important, because more often than not, Suppression relies on a LOW impedance earth ground to be effective. Shielding ALWAYS relies on a low impedance earth ground to be effective.

So, what is the big deal about grounding you might wonder. Well, even the *best* conductors have resistance. If you flow enough current thru a conductor, you WILL drop voltage. The larger the resistance, the more voltage you will develop for a given amount of current. Again, with the massive amounts of current developed by lightning, you want the aboslutely lowest impedance to earth ground you can get.

Not sure about where you live, but where I live, that is a problem. Although most homes where I live the ground rod is not visible, most of the time I have seen them use galvanized ground rods. There is nothing wrong with that in itself, except the conductors used to attach to the rod are usually copper. Galvanized doesn't "talk" to copper very well, and you end up with "dissimilar metal corrosion" over time. So your "ground" although will still protect you from electrical shock from a major appliance malfunction, it doesn't help much in the way of nearby lightning strikes because as the corrosion builds up, the more "resistance" to earth ground it has, and the more voltage is allowed to develop on the "ground" conductor during storms.

So, start with a good ground, along with shielded cable, and quality surge suppression, and you should have a nearly bulletproof (notice I said "nearly!) setup.

In my case, I have driven a copper clad steel ground rod next to the main service ground, and tied the two together (very important-if you don't, you will have dissimilar imedances from the two grounds which will manifest itself as ground loop issues, and actually increase the likelyhood of damage from lightning due to the difference in potential of the two separate grounds). I have also brought in 2" wide ground strap that we use in our industry (heavy guage wire should do nicely; the bigger, the better), and attached it to my ethernet rack, grounding all equipment that is bolted to the rack.

The last thing I need to do, and was the whole purpose of this thread, is rip up ALL my cat5/e in my house and re-run it with SHIELDED cat5/e. The important thing with shielding, is you only ground the shield on ONE END only, which means my distribution point, all shieldes will get bonded to the ground strap, which should majorly reduce the amount of damage I am taking.

So, my point of this post (aside from making myself feel better) was that if you are doing new construction, and you live in an area that is prone to nearby lightning strikes (ask you neighbors if they have every suffered any losses from storms), then take the time to do it right with shielded cat5 cable, a good ground, and adequate surge suppression.

A good link on why shielded cat 5 is here:

http://www.belden.com/pdfs/Techpprs/...ghEnoughtp.pdf

Especially scroll down to the part about EMI/RFI; although they do not specify lightning directly, actually lighting is form of EMI/RFI-just a REALLY POWERFUL version of it.

Everyting you wanted to know about grounding and suppression:

http://www.polyphaser.com/technical_notes.aspx

I hope this boring rant helps someone out there!

-Alan
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post #2 of 7 Old 05-25-2007, 01:14 PM
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Shielding the cabling in your house is not the answer. First question, how many lines come in your house from outdoors? Where are those lines bonded to ground? If the answer is not "right where they come in", you have found your problem. Interesting note, most surge related damage in a home has nothing to do with your power lines. IMO surge supression for each of your incoming services (line and low volt) at the service entrance is a good idea.

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post #3 of 7 Old 05-25-2007, 01:54 PM - Thread Starter
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Actually, all my service cable grounds are bonded to a common ground right where they come in the home (power, phone, and 4 runs from the dish). I agree that most surge related damage doesn't come from the power lines as well. However, proper grounding and shielding of signal cabling can reduce lightining induced damage. Under most circumstances, nothing special needs to be done, but ethernet is a completely different animal:

That was kind of why my post was as long as it was; A nearby lightning strike will induce voltage into nearby conductors. The longer the conductor, the more energy will be induced into it. With unbalanced conductors (such as coax), if the shield is tied to ground at some point along the chain, and it usually is, (remember more than one path to ground can create loops), then the shielding itself will help protect the inner conductor from having current induced into it by a nearby strike. Ethernet however, is balanced, but typically unshielded.

While the nature of a balanced circuit is immune to common mode interferance, a nearby strike could easily cause currents to be induced into the conductors of an ethernet cable since they are "unshielded". Currents of sufficient magnetude will cause more voltage to be developed on the conductors than the normal operating voltages typically present, which will of course wipe out the connected end devices.

You can use surge suppression with ethernet, but in rather large networks, it gets terribly expensive; especially since you need to protect both ends of the cable run.

On some web searching, I have found quite a few stories very similar to my own where some people are claiming that ethernet is a very poorly designed system for these very reasons (I don't agree with them, but without any shielding, long runs and complicated networks within storm heavy areas are going to be prone to damage).

As I mentioned above; you typically either live in an area that is problematic to lightning, or you don't (if you didn't read my entire long drawn out novel above LOL, at least skim it for my neigbor's flagpole comment!).

-Alan

PS Where I screwed up in all this; I knew better. But given the popularity of UTP cabling in ethernet networks, and the fact I don't have a radio tower in my backyard I didn't worry about it; Big mistake, bad idea.
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post #4 of 7 Old 05-25-2007, 03:38 PM
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Do you have UTP run underground outside? If yes, install a TVSS on it if no, where is the induced current coming from? Its not from inside the house...

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post #5 of 7 Old 05-25-2007, 05:54 PM - Thread Starter
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I do not have any outdoor runs. All my wiring is ran in the attic; the induced current comes from nearby lightning strikes. The electromagnetic energy from a nearby strike can *easily* penetrate the wooden roof. Again, I have several neighbors with flagpoles up, the nearest is only 30 ft away from one of my runs.

One of those last two links I provided on my initial thread contains a WEALTH of info on the behavior of lightning and how to combat its effects. They are amoung the very best I have found.

-Alan

-EDIT- I should have probably clarified my rant above that I was mainly concentrating on ethernet specifically, although the theory applies to all conductors as well, but since coax cable typically has the shield grounded, I probably could have just elminiated it in my discussion above.

This paper sums up my first post pretty much. It basically says everything I did above in the first paragraph:

http://www.polyphaser.com/NR/rdonlyr...187/TD1021.pdf

Although it doesn't specificly state it, if you cannot shield the building, a more practical solution is to shield the conductors (use shielded cabling, that is properly grounded-that is the drain wire is connected to earth ground at one end only).
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post #6 of 7 Old 05-25-2007, 06:51 PM
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Is it safe to run grounding straping long distances through the house? I need to tie my antenna to a ground. However it is halfway down the house from the main electrical ground. Is it safe to run a grounding strap tthrough my crawlspace? What is the best material to use? Just some of the regular aluminum grounding wire? I figure my run would need to be about 50'.

- Brian

CQC user since 2005

SageTV user since 2007

PBX in a Flash user since 2012

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post #7 of 7 Old 05-26-2007, 03:03 AM - Thread Starter
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Ground strap is probably overkill. The only time I have ever seen strap used is in RF applications where radio towers are present at the facility (broadcast radio, Ham radio, etc) since they are usually the highest point in the sky, making them great lightning targets. I just used it because I had enough laying around, and my situation is probably more dire than most since I have "lightning rods" so close to my house.

A single, large guage ground wire ought to be sufficient. Copper wire is fine. I would think aluminium would not be a good choice because of dissimilar metal corrosion.

-Alan
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