Grounding OSP shielding.

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 Question by Brian Hooey posted 26 Oct 2005
 Grounding OSP shielding.
I'm a layperson and I'm trying to connect a computer in an outbuilding to my network in my residense. I've researched this quite a bit, but there is so little about correctly grounding the shielding on the Outside Premisis cabling- at least the play-by-play details. Could you please help me with a few simple questions?

You can see pictures of my network project here:
http://www.windhoverdesign.com/networkcable/sarah.htm

Graybar recommended this cabling:
http://www.superioressex.com/products/premises/ospbrdbd-cat5e.htm
If you go into the PDF line sheet, the exact P/N is 04-003-55.

This cable is "OSP 4-PR Category 5e Shielded with copper-clad armor for EMI/RFI and rodent protection." It will be burried about 2ft. underground in a 1" PVC conduit (which you can see in the above link).

At this moment (realizing that plans change with more information), I plan on terminating this OSP cable at the point it enters the house by using the same type of modular female plugs in an outlet box as the other end of the OSP cable, next to the computer in the outbuilding. Then, I should be able to run an indoor rated patch cable to my Linksys router, about 40 ft. away.

My questions are about the grounding of this shielded cable.

1. I'm getting contradicting information. Do I need to ground both ends, or just one? The one in the house I'll assume will be easier than the one in the outbuilding. If two ends are recommended, doesn't that create possible problems if the two grounds are different? Wouldn't that encourage a current flow along the cable shielding????

2. I have small electrical alligator clamps available. I'm guessing I can just peel back the outer jacket a little and clamp onto the shield and run a small insulated wire to a grounding source? If not, what is the right way?

3. Grounding source??? Our electrical panel's ground wire actually runs right past the point where the cable enters the house. That wire is grounded to the copper water pipe at the point where it enters the house from our well. Is that the ground source I should use??? Is there something different I should do? If two grounds are required, how about the outbuilding? Where should the ground wire connect?

I've tried to make my questions clear. Please let me know if you have further questions. Thank you so much for your help. You were recommended by the cable manufacturer, Superior Essex.
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 Answer by Joseph Golan posted 26 Oct 2005
Dear Brian,

Well so far you are doing pretty well and you seem to be asking the right questions.BTW nice pictures, you guys are going to spoil me, not used to getting such details in the questions.

The answers to your questions

1. You should ground both ends including a "primary protector" rated for at least category 5e. This will protect you and your equipment from a stray lightning strike or other high voltage potentials. Graybar can supply these individual protectors. Yes it could create a ground loop that will cause a current flow. See ultimate answer in #3 below

2. The shielding of the cable also includes a drain wire (same potential as the foil shielding). Use this to bond the shield to ground via the primary protector.

3. Yes the electrical panel ground nd is perfect. Run a minimum of a #6 AWG from the ground buss in the panel to the ground terminal of the primary protector. If you do not have a ground available at the outbuilding, you can either run at least a #6 AWG from the panel in the main house to the outbuilding in the same conduit as the category 5e or you can have a 2nd ground rod buried at the outbuilding or for the best of both worlds, do both. Keep your ground wires as short as possible.

You should always check with your AHJ (Authority Having Jurisdiction) as to your local codes regarding this, typically this would be an electrical inspector covering your local.

Of course there are other options: fiber optics; and wireless which will eliminate the ground loop potential problem.

BTW are you also running a second (or third cable) for voice? These should be protected in a similar manner.

Good luck with your project.

Sincerely,
Joseph Golan, RCDD

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