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Thread: Using 1 core as an earth?

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    Using 1 core as an earth?

    Hi Guys

    Let me start of by saying I am not an electrician :-)
    Can anyone please give me some guidance on the below

    Our contractor did an installation and used a 4 core armored cable. As it is a single phase supply, he used one of the cores as the earth. Our client has now rejected the installation as they say the Earth has to be a separate bare earth cable and we cannot use one of the cores.

    In speaking to a few people I am getting conflicting information whether this is a legal installation or not.

    Can anyone give me a definitive answer on this with reference made to a specific section in SANS so I can show the client

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    theres nothing wrong with using one of the cores as an earth. i prefer it to separate earth wires. the armouring must still be earthed as well. the core can be stripped bare on the ends or green/yellow heatshrink used to show its an earth wire. sorry i dont have my sans book to reference.

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    Diamond Member AndyD's Avatar
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    TBH this is something that immediately gets my back up and I point blank refuse to work that way with clients, consultants or architects. If a client has an issue about the way something is installed then the onus is on them to provide a regulation and motivate in writing how the method of installation is not compliant or not safe. In many circumstances there's no regulation that states specifically that an installation method is compliant, often the regs only state certain methods that aren't compliant so it's almost impossible to find a regulation to specifically justify many things that are perfectly good practice.

    I'd strongly suggest you put the ball back firmly in their court and demand they cite the regulation they believe is being breached and gives them the grounds to reject the installation. If no regulation is forthcoming I'd send them a quote for reinstalling it their preferred way as an extra and tell them you're happy to do it as soon as they give you a variation order or a works order to cover your extra expense.

    My thoughts on this particular issue of using one of the internal conductors of the cable as an earth are exactly as Bergie says, there's no reason it isn't good practice. Yes, the cable sheath must also be bonded to earth but that isn't the reason they've stated in their rejection. I certainly don't know of any regulation requiring the earthing conductor to be a separate bare copper conductor or forbidding the use of a conductor internal to the cable that's correctly identified. I'd suggest your responsibility ends with you showing that the Zs earth impedance tests comply and required fault disconnect times are achieved. If they wanted it installing by a method of their preference they should have stated it in their specifications or requirements at the tender or quotation stage of the job rather than after the installation is complete.
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    Quote Originally Posted by Chilli View Post
    Can anyone give me a definitive answer on this with reference made to a specific section in SANS so I can show the client
    SANS 10142-1 section 6.3.3 Identification.

    Interpretation is covered by Bergie and Andy's responses above.
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    Hi Guys

    Thanks for the above clarifications. It is as I thought. Luckily the client has given us a concession on the sites we have build to date, and instruction issued moving forward to comply with the way they want it. So there is no reason to get the boxing gloves out against my client which is something we all want to always avoid

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    The only issue i have with people using one of the cores of a 4 core cable is when they use the yellow as the earth and the black as a phase wire. It becomes a dangerous installation for the "semi skilled" working on installations.

    Many years ago when the colour code was red/white/blue/black, using the black was a standard practice, you just stripped back the black core and used it as an earth.

    The new cables are red/yellow/blue/black. I have seen some imported machines use the black as a phase wire. For people who use a little common sense it is fine, common sense is no longer common.

    With all the new regulations and new SABS edition you would think this kind of issue would be addressed.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by ians View Post
    ......I have seen some imported machines use the black as a phase wire.......
    Although the SANS10142 regs stipulate neutral must be black, this is contradictory with where the black wire is always a phase wire (L2) with the newer 'harmonised' IEC 60446/60455 wiring colours (brown is L1, grey is L3 and blue is neutral). It's not just imported machines, many of the trailing cables like HO7RN-F and HO5RN-F regularly come in these colours from wholesalers in South Africa. If one of these trailing cables is connected to a cable with the old colours then the neutral would change colour from black to blue at that point.

    Then you get the 4-core trailing cables with conductor colours red, yellow, blue and black. Many motors for example don't use a neutral, just 3 phases and earth so what colours do you use for phases? If you use red-yellow-blue for L1-L2-L3 then you're left with the black as earth.

    Then there's the American colours where in a standard single phase appliance plug the black is live and the neutral is white, the NEC 3-phase colours are brown, orange and yellow with grey neutral.

    Bottom line, especially with machinery you've got to expose and visually inspect the internal wiring terminations to ensure what colour in the appliance flex is neutral. Never assume. Any installation is a dangerous installation for unskilled or semi-skilled people to be working on.
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