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Old 4th May 2006, 05:17 AM   #1
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Question newbie question: screened mains lead

Hi,

I have a real newbie question.

When making up a mains lead for a piece of audio equipment, using screened mains cable (3 core, live, neutral and earth, with additional outer screen braid). At which end,if any, to I connect the screen/braid to earth?

-kindest thanks in advance for your answers
Rav

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Old 6th May 2006, 10:46 AM   #2
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Hi Rav. Firstly to comply with forum rules I must mention the danger of working with mains electricity and if you are in any doubt you should consult an electrician etc.
I personally wire my cables as normal but with the braid/screen carefully attached to earth at the plug (Wall socket) end. The idea supposedly being that the screen acts like an antenna and picks up any R.F. interference and drains it to earth. Just be careful not to let the braid/screen lie uninsulated near the Live or Neutral terminals in the plug. I use carefully placed heat shrink around the braid but I have seen drain wires used instead.
If there is any doubt get a professional to at least check it for you before use!

P.S. I'd also like to hear any other views on this topic from other members. Would it be so bad to earth both ends of the screen?
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Old 6th May 2006, 11:17 AM   #3
zanash is offline zanash  United Kingdom
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Why allow any nasties into the ground of the gear ?

I always do as you have suggested.....!

Another point to remember is that you will need about 2m of power cable ....as IMO they act like filters [ Eupen etal]. Hence the argument about 100km HT cable etc is balony!

Good power cables will always provide an improvment over standard power cables ....if your not hearing it you need to look at other areas to find out why your not hearing the improvment ...again IMO.

Also you do not need expensive power cables, just good engineered cable built to shield mains from EMI/RFI thats well shielded, decent stranded copper rated to 1.5amps for preamps cdp etc. Don't skimp on the connections either.

Clean the pins, fuse, fuse holder during assembly and You may just be suprised at how much effect a power cable has.
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Old 6th May 2006, 03:40 PM   #4
phn is offline phn  Sweden
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Do not connect the shield at both ends.

"[Supra] LoRad is the sole audio grade mains cable in the world with full European safety approval."

I believe the LoRad only has an ungrounded foil. It seems shielded mains cables are only approved for installation cable within the EU. Which, in turn, can only be installed by professionals.

The installation cables I have running on some walls in my old appartment have the shield grounded at only one end.
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Old 6th May 2006, 04:06 PM   #5
zanash is offline zanash  United Kingdom
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I think you'll find Eupen and others do to............though I've not checked but ! [happy to be proved wrong!]

I'd be amazed if they did not, otherwise would they be able to sell any?
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Old 7th May 2006, 03:49 AM   #6
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Hi all,

many thanks for your replies. In the interim, I found a link on the TNT-Audio web site with some DIY recipies for audio mains cables, and they confirm that the shield is to be connected at the mains plug end.

I just need to find a primarily safe, and secondarily neat and tidy way of insulating the braid/shield inside the mains plug so that I can connect it to the earth terminal. Green heatshrink is probably my first port of call.

I had been looking at Supra LoRad, but it is impossible to source this locally. Pioneer Australia has been appointed the local distributor for Supra products here in Aus. I contacted them by phone, but they admitted to me that they have not yet had time to source suitable retail outlets. I think I may finally bite the bullet and order some over the web from a supplier in the UK.

(Also with Supra LoRad, I believe the earth conductor has semi-conductive insulation, so there is no need to do anything with the foil at either end of the termination. Am I correct here???)

Anyhows many thanks for your help, and just to reassure you, I always careful test my mains leads with a DMM. And also safety testing and burn in is performed by connecting my latest DIY mains cable to my wife's PC before it goes anywhere near my amplifier!!!!

cheers
Rav

P.S. So far I have only made one mains lead, using stranded 15A rated mains flex from Bunnings (our local Home Depot/B&Q equivilant). I used a Clipsal industrial series mains plug (very pretty made of clear acrylic material, and chunky too!), and a Schurter IEC female (from Farnell). This replaced a stock 10A rated mains lead. With the 15A flex, I noticed a small but significant improvement in bass weight. All connections were cleaned with Caig DeOxit.
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Old 17th May 2006, 04:08 AM   #7
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Don't forget to replace all your house wiring with screened cable.
And don't forget to screen the cable between the house and the street. Oh, and all the way up to the pole pig, back to the sub-station, through that and across the country back to the generator. Your star ground should be at the generator.


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Old 17th May 2006, 05:32 AM   #8
lndm is offline lndm  Australia
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(the generator)

Not to say it won't have any effect whatsoever

IMO the biggest concern with shielding your power cable is the complacency it may bring. Don't forget your RF filtering at your devices power input.
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Old 17th May 2006, 05:49 AM   #9
zanash is offline zanash  United Kingdom
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Twospoons

your missing the point either in jest or what ever...

You have not read up on the Eupen as I suggested..

Mains cable act as filters, use the water mains as an analogy ....if you have dirty water you use a filter.

I'm always amazed when people persist in perpetuating myths, especially audio myths. Eupen are a very large european cable maker , I would take their explaination of how mains cable work over hearsay everytime!

I'll see if I can track down the exact info ...again!
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Old 17th May 2006, 06:05 AM   #10
zanash is offline zanash  United Kingdom
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This section has been lifted from Eupens technical bits

http://www.eupen.com/cable/emc/emc00.html

"By coating conductors with a thin layer of ferrite compound, high frequencies will be strongly attenuated, because their energy will be absorbed by the ferrite powder.
This applies to high frequency disturbances that are propagating on the conductor and which we don't want to disturb the environment, as well as to surrounding interferences, which we want to prevent from disturbing the signals on our cable.

The attenuation that is obtained is proportional to the cable length.

Moreover, the ferrite layer's continuous spreading over the whole cable length makes sure that there will be no sudden changes in characteristic impedance along the cable. Otherwise, such discontinuities might cause high frequency signals to be reflected at those spots and to be sent back to the mains or to other devices."

Now this of course doesn't telll you everything and you have to read ...yes read it yourself. But I feel this goes a long way towards explaining why mains cables have an affect on the sound of music reproduction.
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