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Cable in Buried Conduit

Nick Smith
Hi folks

I'm having a bit of a discussion about what type of cable is suitable to be buried in ducts. My reading of the BS7671 is that only multicore armoured cable should be direct buried or buried in ducts based on Table 4A2 (p390) and the fact that there are no current ratings for installation method D for anything except multicore armoured.


But Table C1 of the on site guide states that twin and earth is "For use underground in conduits or pipes".


My actual problem is being asked to comment on a design where 1c XLPE/AWA cables have been direct buried and also H1Z2Z2 singles have been installed in underground ducts. The H1Z2Z2 data sheet states that it can be installed in ducts, but I am taking that to mean ducts that are not buried, so I am almost sure that this is not acceptable.


Any comments appreciated.


Thanks

Nick
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  • 0
    Thanks very much for the responses.

    I had fallen into the trap of thinking of confusing Informative and Definitive. You are correct, the H1Z2Z2 cables are used to connect solar arrays and have an OD of about 6mm. They are is a separate duct so there is probably a reduced risk of damage during installation. I still have a couple of concerns: -
    • I do not have a specification for the XLPE/AWA and it is being used at 1500VDC, which is worrying me as I can't find a 1c XLPE/AWA cable at that voltage rating.

    • The site is very wet, with the cable trenches filled with water to almost ground level in the photos I have seen. The ducts seem to be sealed ok and there are some H1Z2Z2 cables that are rated for immersion in water. 

    • Technically the BS6724 AC cables (direct buried) are not rated for immersion, although from experience this is not likely to be so much of a problem unless the sheaths have been damaged.


    I think I need more information to see if there is a problem or not.
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  • 0
    Thanks very much for the responses.

    I had fallen into the trap of thinking of confusing Informative and Definitive. You are correct, the H1Z2Z2 cables are used to connect solar arrays and have an OD of about 6mm. They are is a separate duct so there is probably a reduced risk of damage during installation. I still have a couple of concerns: -
    • I do not have a specification for the XLPE/AWA and it is being used at 1500VDC, which is worrying me as I can't find a 1c XLPE/AWA cable at that voltage rating.

    • The site is very wet, with the cable trenches filled with water to almost ground level in the photos I have seen. The ducts seem to be sealed ok and there are some H1Z2Z2 cables that are rated for immersion in water. 

    • Technically the BS6724 AC cables (direct buried) are not rated for immersion, although from experience this is not likely to be so much of a problem unless the sheaths have been damaged.


    I think I need more information to see if there is a problem or not.
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