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PV submain cables: 712.521.101

Jam

Hi all,

To paraphrase the regulation (not a verbatim quote, my emphasis), "Cables on the DC side shall be selected so as to minise risk of faults. This shall be achieved by (i) single-core cables having a non-metallic sheath or (ii) singles in individual conduits. Other types of wiring system providing an equivalent level of safety are not precluded"

So... this appears to be a conflict between a "shall be XX" and "other options are available".

  1. Should this really be read as "This could be achieved by"?
  2. Does a cable construction such as single core two layers of insuation* under a wire/tape armour with non-metallic sheath give you an option for burial of larger DC main/submains? I feel like it strictly does, but isn't what the authors had in mind when drafting the description... but I also think it gives the same degree of safety (or potentially improved)

*No, I don't mean bedding

I note that this is a watered down version of the DFPC that didn't have the opt-out clause.

Thanks in advance for your thoughts.

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    I think the answer is tied up in Chapter 41, Section 412.

    Two layers of basic insulation is not necessarily considered to be equivalent to 'double insulation' - but the examples cited in 712.521.101 definitely are.

    Regulation 412.2.4.1 tells you what is acceptable for wiring systems, and the examples cited in 712.521.101 align with this. You can't just put insulating sleeving over a single insulated conductor and say it's equivalent to double or reinforced insulation.

    Note that in all of these examples, both Regulation 412.2.4.1 and Regulation 712.521.101, consist of basic insulation, plus non-metallic mechanical protection.

    Further, Regulation 522.8.10, as Andy points out, means that the armour ought to be earthed, and double insulation from earth is required.

    A suitable alternative for burying may well be a cable equivalent to BS EN 50618, in a suitable plastic underground conduit, such as 750N twin-walled ducting - provided it's appropriately sealed of course, and at the ends to prevent entry of flora and fauna.

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  • 0

    I think the answer is tied up in Chapter 41, Section 412.

    Two layers of basic insulation is not necessarily considered to be equivalent to 'double insulation' - but the examples cited in 712.521.101 definitely are.

    Regulation 412.2.4.1 tells you what is acceptable for wiring systems, and the examples cited in 712.521.101 align with this. You can't just put insulating sleeving over a single insulated conductor and say it's equivalent to double or reinforced insulation.

    Note that in all of these examples, both Regulation 412.2.4.1 and Regulation 712.521.101, consist of basic insulation, plus non-metallic mechanical protection.

    Further, Regulation 522.8.10, as Andy points out, means that the armour ought to be earthed, and double insulation from earth is required.

    A suitable alternative for burying may well be a cable equivalent to BS EN 50618, in a suitable plastic underground conduit, such as 750N twin-walled ducting - provided it's appropriately sealed of course, and at the ends to prevent entry of flora and fauna.

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