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Direct Buried cables within a controlled area and what constitutes mechanical protection

Former Community Member
Former Community Member
Hello 


I have a  query raised by a client stating that a PV solar Generation site built on agricultural land is non compliant due to direct buried cables. 

Some of the DC string cable is direct buried roughly at 600 depth laid within  cable sand and protection tape over. 

The cable spec is EU and states is suitable for direct burial. 

The protection system constantly monitors the  insulation resistance and dis engages the inverter upon fault. 

The client has stated a non compliance due that no mechanical protection has been installed underground but all cables above ground are mechanically protected. 

  • 0
    Exactly my thoughts These sites come under ESQCR as they are Power stations

    I probably wouldn't go there. Reg 19 of the ESQCR demands that buried cables have "an electrically continuous metallic screen connected with earth" and as the ESQCR is (secondary) legislation, rather than merely a British Standard, non-conformity might be an even more serious matter.

       - Andy.
  • 0
    Do you mean  section 13 ?


    It needs reading with the section before. Note the bold which exempts generating stations or substations..


    12.  No generator or distributor shall use any of his underground cables and associated equipment (except those in generating stations or substations) which he knows do not comply with regulations 13 and 14.

    Protective screens


    13.—(1) Underground cables and associated equipment which contain conductors not connected with earth shall be protected in accordance with paragraph (2).


    (2) The protection referred to in paragraph (1) shall comprise—


    (a)in respect of joints or terminations of a conductor in a low voltage system, some form of mechanical protection; and


    (b)in respect of any other part of any conductor, an electrically continuous metallic screen connected with earth,


    so placed as to ensure that, so far as is reasonably practicable, any tool or device likely to be used in the vicinity will make contact with that protection or screen before it can make contact with any conductors not connected with earth.
  • Former Community Member
    0 Former Community Member
    Did the client require/specify a BS7671 compliant installation and left it to the designer/constructor/inspector&tester to achieve this?


    A simple yes or no would suffice......


    Regards


    BOD
  • 0
    Do you mean section 13 ?

    Oops, yes I did.

    It needs reading with the section before. Note the bold which exempts generating stations or substations..

    Double Oops. I sit corrected (once again) - apologies for any confusion.


       - Andy.
  • Former Community Member
    0 Former Community Member
    IET code of practice for grid connected solar PV systems 2015 section 8.2.  states in blue mandatory text General BS7671 requirements are for AC only 

    BS EN 62446 covers the PV DC side 

  • 0
    RE Elltec:

    IET code of practice for grid connected solar PV systems 2015 section 8.2.  states in blue mandatory text General BS7671 requirements are for AC only 

    BS EN 62446 covers the PV DC side 

     


    That sounds very peculiar to me - BS 7671 section 712 is full of requirements for the d.c. side and written in the usual section 7 way of modifying the general requirements - they'd hardly made sense as 'stand alone' special installation requirements.


    As far as I can tell BS EN 62446 only covers "Requirements for testing, documentation and maintenance" - so nothing about design or installation - was the quote perhaps taken from a section concerned only with ongoing maintenance and testing perhaps?


       - Andy.


  • 0
    The idea that BS7671 covers generating stations is not correct. Even the ESQCR is rather vague on this. I suggest again, the "consultant" is wrong. Suggest this to him and ask for evidence, that usually works for me! BS7671 does not cover generation, the Grid, or anything else except after the meter. Where are the metallic sheaths on EHV overheads? You say not buried, I suggest you look at the superconducting connections.

    Added as edit. The scope of these things is set out, it is much more important than the content!


    David CEng etc.
  • 0
    That'll be gnaw.

    Grumpy. BSc. MSc. Pedant etc.
  • 0
    Grammarly....
  • 0
    Sadly I disagree with some of the above sentiments regarding scope. Leaving the not irrelevant question of contract (which BOD is right to question) to one side for a momeent...
    This is not an installation that comes under BS7671 is it?

    Au contraire: See the list of scope-inclusive items of BS7671 110.1.1, particularly (xviii), which is pretty unambiguous, and in that light I would suggest that the onus is on others to say how it is excluded by the list of 110.2.

     
    IET code of practice for grid connected solar PV systems 2015 section 8.2.  states in blue mandatory text General BS7671 requirements are for AC only


    This is well and truly out of context. Section 8.2 is titled "AC system requirements: Low Voltage" so "The A.C. circuit [...] shall be designed and installed so as to comply with the requirements of BS 7671" doesn't have any bearing on DC. There are many references to BS7671 for the DC design.

     



    BS EN 62446 covers the PV DC side


    Yes it does, for inspection, testing and maintenance, not design. However the same does require verification to IEC 60364, the national implementation of which is BS 7671 (though some other national version could conceivably be used if allowed in the contract). Depending on the vintage of the installation, (BS) IEC 62548 may also have applied to the design.

     



    “generator”  means  a  person  who  generates  electricity  at  high  voltage  for  the  purpose  ofsupplying consumer’s installations via a network

    ... But PV installations generate at low voltage (<=1500Vdc). They connect at HV. If you don't accept that, I don't see what there is to differentiate between that and a factory supplied at 11kV with a 20kW system on the office roof; after all from the DNO's perspective they're both now SSEGs (or PGMs in the new G99 lingo). So I would argue that they're not generators for the purposes of ESQCR. Indeed I would suggest that classing them as generators creates more problems than it solves (random example do any solar parks take any precautions to ensure continuity of the HV supply neutral?). They may however be persons operating a source of energy in parallel with a distributor's network, which sounds the same, but isn't by definition. Odd as it sounds absent further guidance (which to be fair I would welcome) I would go out on a limb and suggest the best classification in terms of ESQCR is that of consumer. (So no TN-C for you!)



    The above all considered, I would return to BOD's very pertinent question and add that in all the design projects I have seen for solar parks, the client has specified BS7671 in the contract specification and often the Connection Agreement with the DNO often stipulates the same.

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