Lightning protection for outdoor ethernet Grounding rod questions etc..

}I have a ethernet cable that runs from my house to an out building at my }house. I live in Florida and we have a real problem with lightning around }here. I plan on using a a TII telephone lightning arrestor on each end.. I'm }talking about the kind that the telephone company puts on the side of your }houese with the gas arrestors inside. } }I think this will work but I have one problem.. I don't know if a ground }rod at the out building will be enough to ground a lightning strike.

You are asking for trouble. A telco lightning arrestor might protect a phone, while not protecting your PC.

Safest bet: go fiber optic outside...used fiber-optic-to-RJ45 adapters aren't that much, and if you buy a piece of fiber with the ends already on, you won't have to pay for attaching the fiber ends.

Stan.

If you drop a ground rod at the outbuilding it will need to be bonded to the rod at the mains. Check the codes for the gauge of the wire needed.

Leonard

It's not just lightning that will be a problem with this arrangement. You'll get all kinds of induced pulses and currents in the wire. If you have to use copper, use opto isolators. Better yet, use fiber between buildings with a media converter if needed. Using copper between buildings like that is asking for trouble.

Michael Kennedy wrote:

I would (did) go underground for this application. (Run a ground wire along with the Cat5).

I had the same setup: outbuilding with house around 75' away. I buried a 2" plastic conduit when I had my water line replaced; but one wouldn't really need to bury it as deep as I did. A foot or so would be sufficient for low voltage stuff...not so difficult in Florida's sandy soil...a real BEAR in Tennessee clay. I ended up running two cat5's, a

12 gauge ground wire and RG59. I used on cat5 for networking, one for three phone lines and the coax (of course) for cable. I actually had originally run thinnet coax in there, but there was plenty of room for everything. I had 360 degrees of bends in the system, so installed access points where it came out of the ground.

I put in a nylon pull line when I installed the conduit, with plenty of slack at both ends so I could pull either direction. Total cost for plasitc conduit, connectors and glue was less than $100, IIRC. Alas, I sold the property for development. I wonder if they dug up my conduit....?

I'd like to do the same at my home, but I'm looking at bedrock less than three inches under the grass in places along the intended route.

jak

Jak's got the right idea, definitely go underground with Cat5 and an earth wire to get rid of the difference in earth potential. If there is no way underground then go fibre. I can make you up a 2 core fibre cable with ST style connectors any length you like. The only real cost is in the media converters.

Well the cat 5 has been ran for about 4 months now and has been working without any problems. Would the ground be just for the difference in earth or would it be to catch stray lightning also..

-Mike

Overhead or underground makes little difference. Both suffer from the same transient threats. You must do the same well proven, reliable, and simple solution that the telephone company uses to connect their building to every other building in town. Each structure must have its own single point earth ground. Every wire entering / leaving the structure must first make a connection to that earth ground.

Locate the NID box (or equivalent) provided by telco. It also has a 'whole house' type protector. What is it earthed to. That (should be) your building's earthing electrode. Telephone wire earthed for same reasons that ethernet cable must be earthed.

For CAT 5, that connection cannot be hardwired to all eight wires. Therefore we use a surge protector. Notice the only purpose of a shunt mode protector - to make a connection to earth.

This industry professional demonstrates the concept with two structures. Both structures have their own single point earthing. Even the incoming underground phone wire is earthed where it enters the building. And to make those structures even more robust, separate earth grounds are interconnected:

To earth the CAT5, one manufacturer provides an earthing protector:

Notice the essential green ground wire. That must make a typically less than 10 foot connection to a single point earthing electrode - at each end of the cable.

How frequent are such destructive transients? > Well the cat 5 has been ran for about 4 months now and has been working

Fifteen ohms isn't bad. I find that much in my dual ground telephone wire.

With lightening the important thing is that you get into the ground in a straight shot - no right angle bends - ideally the ground rod should be directly below the lightning arrestor (and it doesn't hurt to put a ferrite core on the wire into the house). Ground unused conductors in the cable, at the point of use only.

Lightning is fast rise time pulses so you design in terms of good practice for high frequency high power transmitters - large diameter conductors and minimal inductance.

A great technique for an ultra low impedance ground is to take a 10 foot length of rigid copper water pipe and braze or solder a heavy ground wire(s) to it (three inches from one end) and wash it into the ground. Wash it below grade and just have the wire coming out of the ground.

Adapt one of those plastic compression fittings used with "Quest" brand tubing - it will mate with the rigid tube and a garden hose. Get up on a ladder and turn on the water and the pipe will just sink into the soil if there are no rocks. Can't find some plastic compression fittings and you can use brass or just jury rig the hose to the pipe with hose clamps.

It helps to cut the end of the pipe at an angle if you need to work it around rocks. I have had no trouble sinking 20 foot copper pipe down into the water table using that technique.

Some amateur radio operators pack the pipe with salt after it is in the ground, then wash the salt down.

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Why not just do wireless? A couple of the right Linksys or Buffalo, or Belkin wireless routers run in WDS mode will get you encrypted ethernet connectivity with no Ground Potential Rise issues.

or bury the cable

Actually, burying the cable will do little to prevent damage. The problem is due to a phenomenon known as Ground Potential Rise. Lightning striking closer to one building than the other results in a voltage difference between them with significant available current. The whole idea behind surge suppression is to give this current a path to follow through something that is not damaged by this current flow. This site

explains the phenomenon. In my world, I have alot more to be concerned about than lightning induced surges. Contrary to what some people say - "nothing can be done about a direct lightning strike" - this is not true. Lightning strikes occur routinely at my, and many other tower sites with no damage. Lightning is a very short term event - microseconds. a #6 wire can carry the full current of a lightning strike without burning open. That is not to say the point of attachment - of the lightning itself - will not be damaged.

The simplest way to deal with the issue is isolation. This could be wireless, or fiber as others have suggested. Effective surge suppression can be complicated, and requires much more than "putting a surge suppressor somewhere". The basics involve bringing power, and data into a building at the same point. Applying surge suppression to all, and bonding all ground paths to a single point. That is basically what's done on the side of your house where the power, phone company, and cable TV tie their grounds together. It sometimes isn't done well or at all.

Actually, burying the cable will do little to prevent damage. The problem is due to a phenomenon known as Ground Potential Rise. Lightning striking closer to one building than the other results in a voltage difference between them with significant available current. The whole idea behind surge suppression is to give this current a path to follow through something that is not damaged by this current flow. This site

explains the phenomenon. In my world, I have alot more to be concerned about than lightning induced surges. Contrary to what some people say - "nothing can be done about a direct lightning strike" - this is not true. Lightning strikes occur routinely at my, and many other tower sites with no damage. Lightning is a very short term event - microseconds. a #6 wire can carry the full current of a lightning strike without burning open. That is not to say the point of attachment - of the lightning itself - will not be damaged.

The simplest way to deal with the issue is isolation. This could be wireless, or fiber as others have suggested. Effective surge suppression can be complicated, and requires much more than "putting a surge suppressor somewhere". The basics involve bringing power, and data into a building at the same point. Applying surge suppression to all, and bonding all ground paths to a single point. That is basically what's done on the side of your house where the power, phone company, and cable TV tie their grounds together. It sometimes isn't done well or at all.