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Author Topic: Tinkering - grounding spare incoming pair  (Read 222 times)

sheddyian

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Tinkering - grounding spare incoming pair
« on: July 12, 2018, 12:44:35 PM »

This morning I moved the master socket slightly - the Openreach engineer had screwed it to the skirting board, but this made it stick out too much and get in the way of some new blinds I put up the other day, so I disconnected it all and moved it up a few inches onto the wall instead - now the blinds open and close without problem.

While I was disconnecting it, I noticed a 2nd pair on the incoming cable, and vaugely recall discussion on here as to merits (or otherwise) of grounding them to act as a sort of screen, or perhaps to attenuate any ability of this spare pair becoming an aerial.  My incoming cable runs a reasonable distance from a pole.

I checked with a meter that the spare pair wasn't connected to anything - no circuit or voltage across the pair, no voltage or current from either wire to ground.

I stripped the ends of the wires, twisted them together, and twisted on a 3rd wire which I connected to ground.

The result :

Nothing, really.  It all still works, but no speed increase.  There's possibly a slight reduction in CRC and FEC error count, but...

Oh well.  I'll carry on waiting for fibre....  :'(

Ian
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burakkucat

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Re: Tinkering - grounding spare incoming pair
« Reply #1 on: July 12, 2018, 06:49:42 PM »

I'm sure if I searched hard enough I would find other posts on the subject of grounding the unused pair in a two-pair aerial drop cable. I also believe that Walter considered grounding the three steel centenary wires that are also present in such a drop cable. The more I think about it, the more certain I am that a similar discussion took place with respect to nearby atmospheric electrical discharges (a.k.a. lightening).
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sheddyian

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Re: Tinkering - grounding spare incoming pair
« Reply #2 on: July 16, 2018, 11:07:18 PM »

Yes, I'm remembering bits of that now.  And I've just realised I left the ground wire in place, I'd better disconnect it since it's achieving nothing but might make lightning strikes a bit more likely.

Ian
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Weaver

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Re: Tinkering - grounding spare incoming pair
« Reply #3 on: July 17, 2018, 02:16:17 AM »

I do wonder if it might work for me as I have a more sensitive test case. I however already, approximately, have a really bad test case, in that one of my drop cables has both pairs in use and the other drop cable has a noise pickup receiver unused pair.

However, the last thing I would want is to increase the risk of lightning damage still further. How is that ?
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anything