Author Topic: Mains cable where the ground/earth isolation is semi conductive WTF?  (Read 5428 times)

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Offline Kjelt

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I can't believe this is allowed in the EU rules?
One of those weird audio companies sells mains cables where the ground/earth isolation jackets is semi-conductive.
I would love to hear an opinion about this from someone who knows the specific rules regarding mains isolation in the EU.
http://www.supracables.co.uk/mainscables/lorad.html

As I read it, those audio guys sometimes want a foil screen over their mains cables (just like with low voltage audio cables) and normally you solder a drain wire to the earth/ground connection to connect the foil. What they did here is that they made the green/yellow "insulation" jacket semi conductive so there is no need to solder any drain wire.
To me this sounds all alarm bells, I can't believe it is allowed in EU rules.
Quote
Brown (Live), Blue (Neutral) and Green/Yellow (Earth) coloured insulation jackets.
Semi-conductive earth insulation - no drain wires !!
High quality 99.99% coverage foil screen

 

Offline Zero999

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #1 on: February 21, 2016, 11:31:33 am »
The cable screen needs to be properly earthed, not connected via some highly resistive substance.

As far as not insulating the earth conductor is concerned; I believe this is allowed but it would need to be covered with insulated sleeving at the plug and where it's connected to the appliance to prevent it from making contact with live conductors.
 

Offline electr_peter

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #2 on: February 21, 2016, 06:05:58 pm »
I have seen mains cables/wiring with outer insulation and live/neutral/earth conductors, where earth conductor has no insulation - it is bare metal. These cables are used in UK. I guess that insulation for earth is expensive and they chose cheaper way.
Audio cables in question are essentially the same thing as above if used with terminated plugs/sockets on both ends (intended use). Spliced open such cable presents a danger if earth "insulation" is conductive.

I have not seen such semi-insulated cables locally in EU. I do not know whether this is allowed in UK or EU (maybe there are some differences in regulation), but I do not like it either way.
In my opinion and law understanding, insulation 1) should be on all wires including earth and 2) insulation should insulate with very high resistance (>100 of mega ohms).
 

Offline vodka

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #3 on: February 21, 2016, 06:56:20 pm »
Quote
insulation should insulate with very high resistance (>100 of mega ohms).

This is very exaggerate for a line of low voltage. On our regulation(REBT 2002, ITC-BT-19) the insulation between wires for each 1 kV the resistance must be 1 Mohms.
Example : voltage line  of 380 V the insulation among wires must be of  0,38 Mohms
 

Offline Kjelt

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #4 on: February 21, 2016, 07:31:13 pm »
This is very exaggerate for a line of low voltage. On our regulation(REBT 2002, ITC-BT-19) the insulation between wires for each 1 kV the resistance must be 1 Mohms.
Example : voltage line  of 380 V the insulation among wires must be of  0,38 Mohms
That implies that there will continuously run 1mA from mains to earth (0,4W).
35 of these cables will then trip the RCD?  Are you sure the regulation is only 380kOhms so 190kOhms per insulator ?
 

Offline Zero999

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #5 on: February 21, 2016, 07:35:02 pm »
I have seen mains cables/wiring with outer insulation and live/neutral/earth conductors, where earth conductor has no insulation - it is bare metal. These cables are used in UK. I guess that insulation for earth is expensive and they chose cheaper way.
Audio cables in question are essentially the same thing as above if used with terminated plugs/sockets on both ends (intended use). Spliced open such cable presents a danger if earth "insulation" is conductive.

I have not seen such semi-insulated cables locally in EU. I do not know whether this is allowed in UK or EU (maybe there are some differences in regulation), but I do not like it either way.
In my opinion and law understanding, insulation 1) should be on all wires including earth and 2) insulation should insulate with very high resistance (>100 of mega ohms).
I think the problem here is that the screen is not properly connected to earth, rather than the earth conductor having no insulation. The screen must be properly earthed.

Quote
insulation should insulate with very high resistance (>100 of mega ohms).

This is very exaggerate for a line of low voltage. On our regulation(REBT 2002, ITC-BT-19) the insulation between wires for each 1 kV the resistance must be 1 Mohms.
Example : voltage line  of 380 V the insulation among wires must be of  0,38 Mohms
That's the minimum allowed total insulation resistance for the entire appliance/electrical installation, not for a short piece of cable. I would be very suspicious of any piece of cable with an insulation resistance of under 100M.
 

Offline chris_leyson

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #6 on: February 21, 2016, 07:56:36 pm »
Nothing wrong with that, I've got a house full of cables with no insulation on the earth conductor, it's not needed. Insulation on live and neutral is a different matter. Take a look at look at mineral insulated cable for fire alarms ? The outer sheath is just to prevent corrosion.
 

Offline Zero999

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #7 on: February 21, 2016, 08:10:31 pm »
Nothing wrong with that, I've got a house full of cables with no insulation on the earth conductor, it's not needed. Insulation on live and neutral is a different matter. Take a look at look at mineral insulated cable for fire alarms ? The outer sheath is just to prevent corrosion.
That's on the fixed wiring which I believe is different.

Look behind any socket cover and you'll see there should be some green & yellow sleeving over the earth conductor to prevent it from touching the live terminals when the socket is screwed to the wall.

As far as the mineral fire alarm cable is concerned; the outer sheath should also be earthed. If it isn't then it's been incorrectly installed.
 

Offline vodka

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #8 on: February 21, 2016, 08:42:43 pm »
Quote
2.9 Resistencia de aislamiento y rigidez dieléctrica

Las instalaciones deberán presentar una resistencia de aislamiento al menos igual a
los valores indicados en la tabla siguiente:


Este aislamiento se entiende para una instalación en la cual la longitud del conjunto de
canalizaciones y cualquiera que sea el número de conductores que las componen no
exceda de 100 metros. Cuando esta longitud exceda del valor anteriormente citado y
pueda fraccionarse la instalación en partes de aproximadamente 100 metros de
longitud, bien por seccionamiento, desconexión, retirada de fusibles o apertura de
interruptores, cada una de las partes en que la instalación ha sido fraccionada debe
presentar la resistencia de aislamiento que corresponda.
Cuando no sea posible efectuar el fraccionamiento citado, se admite que el valor de la
resistencia de aislamiento de toda la instalación sea, con relación al mínimo que le
corresponda, inversamente proporcional a la longitud total, en hectómetros, de las
canalizaciones.

http://www.f2i2.net/documentos/lsi/rbt/ITC_BT_19.pdf


2.9 Resistance of insualtion and Dielectric strength

     The installations must present a resistance insulation at least equal to values indicated on the next table:

     This insulation understand it  for an installation which the long of set of pipes and anyone that will be the numbers wires that  don't exceed about 100 meters
     
     When this  lenght exceed of values before quoted and it could fractionated the installation by parts approximately of 100 meters of lenght,properly by sectioning, disconnection, take off the fuses or turn off
     the interrupt,each of the parts what the installation have been fractionated must be present the resistance insulation that corresponds.

    When  won't be possible to realize the fractionated quoted, accept it that the value of the resistance of insulation of all installation will be , with the relation to the  minium that it corresponds,inversely   
    proportional to the total lenght,at hectometers, of the pipes.
 

Offline Kjelt

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #9 on: February 21, 2016, 09:31:06 pm »
Interesting, which country is this?
We have the same values in our country BUT for the entire electrical installation, not only the cable
Quote
Conform IEC 60364.6.61 dienen de weerstandswaarden groter te zijn dan 1 megohm voor een testspanning van 1000 V test, 0,5 megohm voor 500 V en 0,25 megohm voor 250 V.
« Last Edit: February 21, 2016, 09:34:05 pm by Kjelt »
 

Offline artag

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #10 on: February 21, 2016, 10:02:15 pm »
The earth wire doesn't need to be insulated, since it's at earth potential (obviously).

The neutral and live wires do need to be insulated and presumably are. Thus there is no leakage into the partially conductive sheath.

The partially-conductive sheath won't screen as well as a metallic mesh, but since it's only purpose on a main cable used to connect audio equipment is for marketing, it's irrelevant.

 

Offline WattSekunde

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #11 on: February 21, 2016, 10:48:52 pm »
The easy way to the right earth potential...



 :clap:
 

Offline ozwolf

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #12 on: February 21, 2016, 10:55:50 pm »
The easy way to the right earth potential...



 :clap:

That picture "terra fies" me!

Ozwolf
I reject your reality and substitute my own.
 

Offline vodka

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #13 on: February 22, 2016, 06:03:46 am »
Quote
Interesting, which country is this?

Spain
 

Offline station240

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #14 on: February 22, 2016, 05:18:46 pm »
The safety risk I see is what happens inside the plug or device it's wired into.
You wouldn't want to route the earth wire over a live terminal by accident.

I found the LoRad data sheet, it's very in-depth  :-DD
http://www.supracables.co.uk/images/catalogues/lorad.pdf

The patent does explain things however.
https://www.google.com.au/patents/EP0746858B1
Quote
an electrically conductive connection conductor is received which consists of semiconductive plastic and is arranged to run helically around the earth conductor, to connect the earth conductor with said cable screen.
 

Offline Kjelt

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #15 on: February 24, 2016, 10:11:23 pm »
Thanks for the info.
Patent is from 96 so almost or already expired. Still wonder who would also produce something like this.
 

Offline Keyrick

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #16 on: February 25, 2016, 11:08:57 pm »
I may be mistaken, but I believe that they are referencing the "Drain", not the "Earth/Ground", based on the photo.  Drain and Earth/Ground (EGC) are not the same as they provide different functions.
 

Offline nogood

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Re: Mains cable where the ground/earth isolation is semi conductive WTF?
« Reply #17 on: February 26, 2016, 12:19:53 am »
The easy way to the right earth potential...

(suicide showerhead)

 :clap:

I know that picture, and now that I watched Bigclive's video on YT about that sort of showerhead, it is even worse *shudders*
 


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