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Lightning protection for outdoor ethernet Grounding rod questions etc..

Discussion in 'Electronic Repair' started by Michael Kennedy, Mar 9, 2006.

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  1. 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. The
    building doesn't have a ground rod right now but I was planning on putting
    one in for this..

    How do you get a good ground with a ground rod. I have tried driving one
    down but when I ohm it there is always a lot of resistance vs the power
    company's neutral / ground. I was told that a good ground rod will have
    about 15 ohms of resistance between the rod and the system ground.

    I would just hook this arrestor up to the out building's ground wire, but
    the ground and the neutral are tied togeather and I don't think there is a
    very good ground out there because the ground on the CATV wire will shock
    you if you touch it and a ground in the building out there. On the voltmeter
    it reads about 3v between the catv wire ground and the bldg ground.. So I
    think my ground is overloaded or has a bad connection at the breaker
    pannel.. It has 2 legs of 120v and one neutral. There is no seperate ground
    wire.

    Thanks for any advice / help..

    - Mike
     
  2. Stan

    Stan Guest

    }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.
     
  3. 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
     
  4. Mike Berger

    Mike Berger Guest

    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.
     
  5. jakdedert

    jakdedert Guest

    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
     
  6. simon hanlon

    simon hanlon Guest

    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.
     
  7. 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
     
  8. simon hanlon

    simon hanlon Guest

    Just to keep the earth potentials the same, I installed a network point in a
    building with a different earth potential than the one across the road on
    the same network. Everytime you plugged the cable in you would get a small
    spark and the network would crash.
     
  9. w_tom

    w_tom Guest

    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:
    http://www.erico.com/public/library/fep/technotes/tncr002.pdf

    To earth the CAT5, one manufacturer provides an earthing protector:
    http://www.tripplite.com/products/product.cfm?productID=151
    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? On average, maybe once
    every eight years. In your locale, well, consider the number as more
    frequent. A number that will vary significantly based upon conditions
    such as geology.
     
  10. default

    default Guest

    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.
     
  11. Bob

    Bob Guest

    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.
     
  12. Jeff

    Jeff Guest

    or bury the cable
     
  13. Bob

    Bob Guest

    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 http://www.gpr-expert.com/
    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.
     
  14. Bob

    Bob Guest

    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 http://www.gpr-expert.com/
    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.
     
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