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Author Topic: Twisted pair or shielded  (Read 2851 times)

Edinburgh_lad

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Twisted pair or shielded
« on: September 13, 2021, 04:53:02 PM »

Hello

So far, I've used an ethernet cable as my extension cable (non-solid core).

I'm looking to get a solid core shielded cable, but unless you buy a 50m reel (I only need 4m!), it's either solid core twisted or solid core shielded (not twisted).

So, the question is: better to get solid core twisted, or solid core shielded (not twisted)? (I feel very Shakespearian asking this question, actually :))

Thank you.

PS if you know of anyone selling solid core twisted and shielded by metre (can be ethernet, too), please let me know.
« Last Edit: September 13, 2021, 04:57:00 PM by Edinburgh_lad »
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Alex Atkin UK

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Re: Twisted pair or shielded
« Reply #1 on: September 13, 2021, 05:03:14 PM »

You only need shielded if:

1) You're running it next to mains cabling.
2) You're running it outdoors where there is lots of radio frequency signals

Also when you do, it MUST be earthed.

Basically shielded is used in building cabling that is more likely to pickup RF from other devices, standard rack mount switches are earthed to deal with this, but consumer routers and switches are not.

If you use a shielded cable without earthing it you run the risk of the opposite, the shield will act as an antenna picking up RF and transmitting it into the pairs.
« Last Edit: September 13, 2021, 08:41:36 PM by Alex Atkin UK »
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licquorice

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Re: Twisted pair or shielded
« Reply #2 on: September 13, 2021, 05:17:19 PM »


Also when you do, it MUST be earthed at both ends.


Noooo, one end only
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burakkucat

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Re: Twisted pair or shielded
« Reply #3 on: September 13, 2021, 05:51:47 PM »

Noooo, one end only

You got in there before me!  :)

(Alex, your topic for research is "ground loop(s)".  ;)  )
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Alex Atkin UK

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Re: Twisted pair or shielded
« Reply #4 on: September 13, 2021, 08:42:48 PM »

Noooo, one end only
You got in there before me!  :)

(Alex, your topic for research is "ground loop(s)".  ;)  )

Thanks, corrected my post.

I'm not sure why I posted both ends as at the back of my mind I did remember something about one end due to ground loops, but I somehow got distracting when double checking it and posted before I'd done my due diligence.

Fortunately its a post here, I would have gotten my ass handed to me on any other forum.  ::)
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Edinburgh_lad

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Re: Twisted pair or shielded
« Reply #5 on: September 14, 2021, 07:55:03 AM »

Thanks very much all. Really useful to know all the details.
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Weaver

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Re: Twisted pair or shielded
« Reply #6 on: September 20, 2021, 12:11:35 PM »

How does one make an earthed cable connection, practically ? Need a screened cable with a screen-earth attachment point, and some earth cable and something to earth it to.
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Alex Atkin UK

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Re: Twisted pair or shielded
« Reply #7 on: September 20, 2021, 01:24:12 PM »

In practice, its supposed to be earthed at the switch.  A shielded cable should have a shielded RJ45 connector that crimps onto the shield and may also have an extra drain wire you can crimp onto the outside.
« Last Edit: September 20, 2021, 01:32:05 PM by Alex Atkin UK »
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burakkucat

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Re: Twisted pair or shielded
« Reply #8 on: September 20, 2021, 04:40:36 PM »

In practice, its supposed to be earthed at the switch.  A shielded cable should have a shielded RJ45 connector that crimps onto the shield and may also have an extra drain wire you can crimp onto the outside.

If you check the specification either for a Registered Jack 45 (literally a specific sized US telephony socket and nothing to do with Ethernet) or for an 8P8C socket and plug pair (which is not RJ45), there is no definition of a screening point connection.

When a building is equipped with structured Ethernet cabling, that cabling (solid core cable) can be screened / earthed. By definition, that structured Ethernet cabling is from a socket to a socket. The normal earthing point would be at the patch panel end, where all of the individual drain-wires are connected to a dedicated low-impedance earth point (and not the building's mains supply earth). Individual, flexible, patch cables (i.e. plug to plug), used to connect equipment to the structured cabling sockets, would have no screening / earthing.

There are certain vendors who will provide what they claim to be "screened Ethernet patch cables". Such products are just snake-oil.  >:(
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benji09

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Re: Twisted pair or shielded
« Reply #9 on: September 20, 2021, 09:54:15 PM »


   Personally, I would not  get involved in screening, as when you do you get into earthing, and earth loops. Also if you earth only one end of your screen, at higher frequencies that screen would look like an aerial, and start picking up other things instead. If you were making a radio transmitter, you would have to watch how long your earth wires were, due to the inductance of the wire.
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Alex Atkin UK

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Re: Twisted pair or shielded
« Reply #10 on: September 21, 2021, 12:44:39 AM »

If you check the specification either for a Registered Jack 45 (literally a specific sized US telephony socket and nothing to do with Ethernet) or for an 8P8C socket and plug pair (which is not RJ45), there is no definition of a screening point connection.

That kinda figures and I always forget its not "technically" RJ45, as it seems the entire industry does too. :/

But in practice, for situations that are not big business structured cabling, its how its done.  That's literally my own switch clearly connecting the sides of the plug to the earth and that plug is what my Ubiquiti Litebeam installation uses.  (an absolutely PITA to wire up btw, the drain wire has snapped off one of them)
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