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Underground Single core AWA in ducting - Compliance with 7671

Dan20387

Hi All

Long time lurker and big fan of the wealth of knowledge in this place and the old forum. 

I have a situation here designing an 200kW EV charger.  The manufacture of the charger supplies a gland plate with 10no entry glands for single cores in parallel.  The distance between the gland plate and the busbars of the charger is quite small meaning glanding and terminating a multi-core cable would make it very difficult to navigate the cores to the busbars.  The charger itself does not require a neutral.  

In appendix 4 in the brown book, there is no reference D for single core armoured cables, just Ref C and F.   When looking further back in the book on p431 is does say that if the specific installation parameters are known (ground thermal resistance, ground ambient temp, cable depth) you can reference the cable manufacture or ERA69-30 series.    I have a copy of ERA which has the current carrying capacity tables for three single core armoured underground but my main question is this:-

Does that paragraph for Ref method D only apply to multicore cables in the ground, and therefore single core AWA buried is not compliant with BS7671 and cannot be certified? 

Thanks in advance  

  • +1

    The short answer is, no. Appendix 4 lists examples of installation methods for various cables, but it is not true to say that if a particular type of cable which has been installed in a particular way is not in the table, it is non-compliant.

    See the notes to Table 4A2 on page 433.

  • +1 in reply to Chris Pearson

    seconded - BS 7671, and for that matter ERA too, can only list a small subset of all possible permutations of cable types, grouping and routing methods,

    You are free to invent your own, but then the calculation of the current rating is, in the manner of the Peter Cook sketch, 'entirely a matter for you' but usually you can use entries for similar situations for inspiration and estimate upper or lower bounds, or indeed measure cables temperature rise yourself.

    Mike.

  • +1

    Dan20387,

    I think I know the charger you are talking about? Think manufacturers name is Al..... and an Italian manufacturer.

    What I have done is get them to supply a gland plate with no entries punched in it. Charger was then installed in two x four core H0FR7 cables in parallel.

    Myself and my clients rejected their standard gland plate and if they wanted our business then supply what we requested.

    Other thing is they supply a connection "Jig" so base plate is bolted onto foundation after you glanded your cables in then you fit the jig. You have tons of space as the main charger enclosure isnt yet bolted on, so you dress/bend/form the conductors. Fit crimps and bolt them to the studs on the jig. That way your conductors are all sorted for install.

    You then unbolt the conductors remove the jig and then the main charging enclosure is lifted on. And because your conductors already shaped and lugged, then easy to then bolt on your conductors. Job Done.

    But, avoid the single armours at all costs.

    Cheers GTB

  • +1

    Firstly the cables a tables information In Appendix 4 are Informative not Normative so do do not make Regulations in themselves.

    I do not know why there there is not a Table for AWA cables in Appendix 4.

    You certainly can bury AWA cables in the ground but check with the particular manufacturer to ensure their AWAs are suitable for direct burial. In propriety design software , mine does anyway, you have a drop down option to use BICC data as BS 7671  does not have this option.

    Hope this helps?

    JP

  • 0

    Thanks for all the replies, 

    The current state of affairs so far is that we're trying to go for parallel Non-armoured PVC/XLPE single conductors buried in ducting with a steel plate above for mechanical protection purely for an easier termination on either side. 

    The problem we're having is trying to get any cable manufacture to provide any current carrying capacities for their cable installed in that way.  It's the same with the H07 rubber cable single and multi-core.  

    The only manufacture I've found so far is BICC in Egypt but I don't really want to start the process of becoming an importer of cable

    https://www.bicccables.com/media/pdf/power-cable-catalogue.pdf  page 70-71 for anyone interested. 

  • 0 in reply to Dan20387

    Might be worth having a chat with Aaron Walstow at Doncaster cables

  • 0 in reply to Dan20387

    There is the option of using the tabulated ratings for cables in single-way ducts in ERA 69-30 (nowadays available from Rina), which, for comfort, is specifically mentioned in BS7671, or even calculation "from scratch" per BS EN (IEC) 60287.

    Doing the latter by hand would be a fair task and also requires specific knowledge of the construction of the cable you are planning to use but there are software tools to do it for you (and indeed consultants who know how to use them if you don't want to and you can't persuade the cable supplier to do it on your behalf).

    Specifically on BICC, you might be interested to know that Amtech/Trimble Prodesign as used by many designers does use tabulated data from the BICC Electric Cables Handbook for some cases not covered by Appx 4 of BS7671.

  • 0 in reply to Jam

    For those interested in the calculation methods but without the few hundred quid for the standard, it is also discussed here

    In this research paper, though you need a clear head to follow it.

    Mike.

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