Mains cable where the ground/earth isolation is semi conductive WTF? - Page 1
Forum section: electronics / general

author: Kjelt
author_rank: Super Contributor
timestamp: February 21, 2016, 11:10:50 am
content: 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.htmlAs 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

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2016, 11:31:33 am
content: 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.

author: electr_peter
author_rank: Unknown
timestamp: February 21, 2016, 06:05:58 pm
content: 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).

author: vodka
author_rank: Frequent Contributor
timestamp: February 21, 2016, 06:56:20 pm
content: QuoteThis 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

author: Kjelt
author_rank: Super Contributor
timestamp: February 21, 2016, 07:31:13 pm
content: Quote from: vodka on February 21, 2016, 06:56:20 pmThat 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 ?

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2016, 07:35:02 pm
content: Quote from: electr_peter on February 21, 2016, 06:05:58 pmI 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 from: vodka on February 21, 2016, 06:56:20 pmThat'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.

author: chris_leyson
author_rank: Super Contributor
timestamp: February 21, 2016, 07:56:36 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2016, 08:10:31 pm
content: Quote from: chris_leyson on February 21, 2016, 07:56:36 pmThat'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.

author: vodka
author_rank: Frequent Contributor
timestamp: February 21, 2016, 08:42:43 pm
content: Quotehttp://www.f2i2.net/documentos/lsi/rbt/ITC_BT_19.pdf2.9 Resistance of insualtion and Dielectric strengthThe 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 metersWhen 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 offthe 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,inverselyproportional to the total lenght,at hectometers, of the pipes.

author: Kjelt
author_rank: Super Contributor
timestamp: February 21, 2016, 09:31:06 pm
content: Interesting, which country is this?We have the same values in our country BUT for the entire electrical installation, not only the cableQuote

author: artag
author_rank: Super Contributor
timestamp: February 21, 2016, 10:02:15 pm
content: 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.

author: WattSekunde
author_rank: Regular Contributor
timestamp: February 21, 2016, 10:48:52 pm
content: The easy way to the right earth potential...

author: ozwolf
author_rank: Regular Contributor
timestamp: February 21, 2016, 10:55:50 pm
content: Quote from: WattSekunde on February 21, 2016, 10:48:52 pmThat picture "terra fies" me!Ozwolf

author: vodka
author_rank: Frequent Contributor
timestamp: February 22, 2016, 06:03:46 am
content: QuoteSpain

author: station240
author_rank: Unknown
timestamp: February 22, 2016, 05:18:46 pm
content: 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-depthhttp://www.supracables.co.uk/images/catalogues/lorad.pdfThe patent does explain things however.https://www.google.com.au/patents/EP0746858B1Quote

author: Kjelt
author_rank: Super Contributor
timestamp: February 24, 2016, 10:11:23 pm
content: Thanks for the info.Patent is from 96 so almost or already expired. Still wonder who would also produce something like this.

author: Keyrick
author_rank: Contributor
timestamp: February 25, 2016, 11:08:57 pm
content: 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.

author: nogood
author_rank: Contributor
timestamp: February 26, 2016, 12:19:53 am
content: Quote from: WattSekunde on February 21, 2016, 10:48:52 pmI know that picture, and now that I watched Bigclive's video on YT about that sort of showerhead, it is even worse *shudders*