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Earthing / screening
2017-09-21, 11:13
Post: #1
Earthing / screening
Much is said on the forum regarding the screening of mains cables if they are running near audio cables be it data or analogue.

This in itself appears an easy problem to fix; for neatness buy some tubular tin coated copper braided sleeving or wrap the mains cables in aluminium foil. My concern is should then the sleeving or foil be earthed and if so where to?

Will the problem of ground loops occur, I know these loops can be cured by isolating one of the ground paths with an isolation transformer, common mode choke, optical coupler, etc. But is there an easier way if such a problem occurs.

I appreciate the EMF issues goes beyond just local power cables to the hifi. However I am now brain dead and totally confused reading all the previous posts.

So to try and keep this on track
1 sleeving and/or foil is it worth while
2 what about ground loops
3 If I can clear the above up then I will put in a dedicated hifi ring main.
Many thanks even my Pookah is confused

Harvey and Pookah
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2017-09-21, 12:58
Post: #2
RE: Earthing / screening
If you are thinking of installing a dedicated hi-fi ring main then see my Post #5 in this earlier Thread (amongst others) :-

http://forums.linn.co.uk/bb/showthread.php?tid=26484

The choice of cables and other components was of course guided at every step by Briain and I have also purchased some DIY shielded power cords from MCRU, again with the earth terminated only at the plug socket end.

http://www.mains-cables-r-us.co.uk/diy-m...d-set.html

So I've made very effort to use shielded cabling, properly earthed, wherever possible and it certainly has made a difference. All the previous snap, crackle and pop from the mains have disappeared - happened every time the fridge or freezer kicked in, when someone turned on/off a light/lamp switch and as for hair dryers - well! General impression is one of a much lower and quieter noise floor but as Briain advised me, after a few months you just accept it as the norm and forget about it.

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2017-09-21, 15:33
Post: #3
RE: Earthing / screening
First step for me is to physically separate all mains cords away from the ethernet cables and interconnects.

This may involve rerouting the cables behind your cabinet, and/or use small pieces of packing foam, or some other means of physically separating them.

Next step is to wrap my ethernet cables in multiple layers of aluminum foil from one end of the RJ45 connectors to the other, without actually touching the connectors.

If you have any mains cables that are touching each other, or ethernet/interconnect, speaker cables, wrap some aluminum foil around the cables where they are in close proximity to each other (where they intersect). You do not have to wrap the whole cable, just that area that is in close proximity.

Because you are adding some aluminum foil around the outside of cables that are already sheathed, I don't ground them, as there is no electrical contact, and should never be any electrical contact.

Tell the Pookah to listen to the music.

BYU

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2017-09-23, 18:11 (This post was last modified: 2017-09-23 18:23 by Harvey and his Pookah.)
Post: #4
RE: Earthing / screening
Thanks for the inputs and of course I have done that dangerous action of trawling the web: did you know everyone is an expert on everything once you hit the web for info. Thanks for this forum where we have some pretty knowledgeable and above all helpful characters.

So as a first stage is there any thing wrong with putting and external shielding over mains cables and terminating at the 3 pin plug end. I rewired the house two 4 years ago (legally) so am aware I need to keep sheath away from the other two pins!

However I am tempted to use polyester sheath carbon impregnated( as Donald has kindly produced a link to) instead of the above and would this eliminate the need to touch the data or analogue cables?

Next what is the advantage of aluminium foil v tinned copper sheathing for the data cables or the analogue cables

If I have screened the mains cables do I need to screen the data and analogue.

I have also read and it makes logic to me is if it has to happen cross power and data at right angles as there is less area for rf interference.

Sorry I will go back to being retired and not trying to recall my electronics knowledge from the 60's. Yes we did have electronics then.

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2017-09-23, 20:15 (This post was last modified: 2017-09-23 20:20 by DavidHB.)
Post: #5
RE: Earthing / screening
(2017-09-23 18:11)Harvey and his Pookah Wrote:  If I have screened the mains cables do I need to screen the data and analogue.

It is the signal leads you are protecting, so yes. The reason for shielding the mains cables, as I understand it, is that, if they are going to induce a voltage into anything, they should induce it into the shield, from which it can leak away harmlessly to whatever is functioning as earth, rather than as noise into the sensitive signal leads. Shielding those as well (or, in my opinion, first) provides the primary layer of protection. FWIW, I tend to shield (or use shielded) signal leads and not power cables, but I do try to separate signal from power leads as much as possible.

David

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2017-09-25, 20:52
Post: #6
RE: Earthing / screening
A 'screen' connected to nothing does not work and is no screen at all. On the contrary, it will act like an antenna. It will radiate and receive any EMC troubles present in the frequency range it is capable of. A proper screen has to be connected to either protective earth or signal ground on one side of the cable. It must not me connected to both sides, as this may create unwanted ground loops.

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2017-09-26, 06:42
Post: #7
RE: Earthing / screening
(2017-09-25 20:52)BB1 Wrote:  A 'screen' connected to nothing does not work and is no screen at all. On the contrary, it will act like an antenna. It will radiate and receive any EMC troubles present in the frequency range it is capable of. A proper screen has to be connected to either protective earth or signal ground on one side of the cable. It must not me connected to both sides, as this may create unwanted ground loops.

Wouldn't it act like a Faraday cage?

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2017-09-27, 18:03
Post: #8
RE: Earthing / screening
In principal yes, but…

Quote:The simplest and most cost effective barrier against electrostatic noise pickup is a conductive shield, sometimes referred to as a Faraday cage. It functions by capturing the charges that would otherwise reach the signal wiring. Once collected, these charges must be drained off to a satisfactory ground (or reference potential). If not provided with a low-resistance drainage path, the charges can be coupled into the signal conductors through the shield-to-cable capacitance (Figure 3).

http://www.vishaypg.com/docs/11051/tn501.pdf

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2017-09-28, 09:34
Post: #9
RE: Earthing / screening
Thanks BB1. An earthing strip from the DSM end of the shielded ethernets connected to the Earth Ground on the DSM seems the neatest way.

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2017-09-28, 11:33 (This post was last modified: 2017-09-28 11:35 by DavidHB.)
Post: #10
RE: Earthing / screening
I hope it is helpful to point out that the term 'earth' or 'ground' may or may not refer to the physical ground. Essentially, it is the zero voltage reference point in an electrical system; anything that can server as that point can be used as the zero reference (or, if you prefer, the return) point of the circuit or group of circuits that make up the device. A mobile phone, for instance, may not be connected to the physical earth, but it still has a return path to the zero reference point, and thus an 'earth'. Mains powered devices, will of course use mains earth as the reference point.

When it come s to the screening of Ethernet cables, I don't know offhand whether the screen is normally connected, but, as there is a return (-) wire in each twisted pair used, there are points in the cable (or more likely the connector) which could be connected to the shield. Even if the shield is not connected, any voltage induced into it will try to find its way separately to an earth point somewhere, and thus dissipate harmlessly, turning the shield into a form of Faraday cage, as previously described.

David

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