Wiring on Fixed installation with class 5 conductor (Flexible Cable). - Wiring and the Regulations BS 7671 - IET EngX - IET EngX

Wiring on Fixed installation with class 5 conductor (Flexible Cable).

Good morning Guys,

I refer to Chapter 52 ( 521.9) of BS 7671, Can we use  class 5 conductor ( multicore Cable) in fixed Installation for wiring lighting, power ? Grateful if someone can help answer with document evidence.

  • As in the Regulation, if the cable is protected against damage, then it is fine to be used.

    Multiple inset downlights use flex, as, basically, the connection blocks for them do not have enough room for 2x 1.5mm T+E cables, so a JB, and a flex off to the fitting is the usual solution.

  • Originally there was a flat prohibition on using flex for fixed wiring (apart from the final connection to fixed appliances) but that originated in the days when flex was much less substantial than premises wiring cables - typically being a couple of rubber singles with little more than a thin cotton braiding over. These days flexes have more robust PVC insulation and a PVC oversheath so apart from the conductor being stranded are pretty much identical and generally just as robust as rigid PVC/PVC cables.

       - Andy.

  • Good afternoon Alan,

    Thanks for Feedback. I am looking for backup where Class 5 flexible cable is clearly mentioned suitable for fixed installations. We follow BS 7671:2018  here.

  • Good afternoon Andy,

    Thanks for Feedback. You comments are quite clear.

    I am looking for backup where Class 5 flexible cable is clearly mentioned suitable for fixed installations. We follow BS 7671:2018  here. If we compare Class 02 versus Class 05. Class 02 conductor is known to be suitable for wiring at fixed installations. But certain projects demands for class 05 flexible conductors. I want to ensure that class 05 usage in fixed installation is good by norms.

  • I want to ensure that class 05 usage in fixed installation is good by norms.

    Well, flexible cables (Class 5 and Class 6 stranding) are actually specified for some installations, or parts of installations, within BS 7671.

    Flexible cables must be acceptable (if properly selected, erected and protected for the installation conditions - as with all cables), because:

    • Regulation 422.3.201 permits their use, although has some requirements for their construction or protection. This is supported by Regulation Group 521.9
    • Regulation 413.3.4 has a particular requirement concerning their use in parts of the installation with protective measure double or reinforced insulation.
    • Regulation 418.3.6 for electrical separation to more than one item of equipment requires flexible cables to incorporate a protective conductor
    • They are required to be used for suspended current-using equipment (Regulation 522.7.2)
    • They are required in installations in flexible structures, or where a structures are intended to be moved (Regulation 522.15.2,
    • There are minimum cross-sectional areas for flexible cables "for any other purpose" in Table 52.3
    • Some Part 7 special locations specify certain wiring systems, for which flexible cables are options, or mandated (Regulations Group 704.522.8, Regulation 717.411.3.1.2, Regulation Group 717.52, Regulation 721.521.2

    Of course, when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)

  • I would add to Graham's comprehensive list that an adjustment is made for flexible cables in Table 4D2A, which very clearly applies to fixed installations, be they in conduit in walls, conduit on walls, etc.

  • Good morning Graham,

    Really appreciated on above points shared. Indeed these were very helpful in getting quite clear on the different applications for class 05.

    Though I noticed from your reply above that below regulations indeed can be used for installing the class 05 conductor ( Heavy duty Type having voltage rating of not less than 450/750V) for Fixed installation with Chris comments on adjustment is made for flexible cables in Table 4D2A.

    • Regulation 422.3.201 permits their use, although has some requirements for their construction or protection. This is supported by Regulation Group 521.9
    • when using stranded wires, appropriate terminals ought to be used, or, Class 5 or Class 6 conductors are to be terminated in terminals suitable only for Class 1 (solid) and/or Class 2 (stranded) they should be suitable prepared, for example with a ferrule. (See Regulation Group 526.9.)
    • Since I don't have BS EN 50565-01 to understand real definition on described on Light, Ordinary, Heavy duty type. Grateful if you can help on same as well. This is part of regulation group 521.9 and 422.3.201.

    Thanks & Regards,

  • Good morning Chris,

    Indeed your reply along with Graham's reply help me reach to my conclusion.

    Since I don't have BS EN 50565-01 to understand real definition on described on Light, Ordinary, Heavy duty type. Grateful if you can help on same as well. This is part of regulation group 521.9 and 422.3.201. I want to clear my doubt on the definition by BS EN 50565-01.

  • The question is the mechanical robustness - flexible cables have the conductor stranded, and how many strands and how fine is the 'class' in this context, the insulation must be more or less flexible, but more flexible cables are more prone to mechanical damage (in simple terms the plastic or rubber scratches off more easily if it is soft, but if it is not soft it does not flex so well ).
    So cables that get dragged over rough ground or concrete, or may be trodden on need harder plastic but are less flexible than those that are gently clamped against a smooth surface and just flex a bit.
    However, for cable that is to reel in and out - as for example on certain types of machine, cranes and so on come to mind, the softer insulation and finer strands are essential. Then there is temperature - some plastics flexible at room temperature become brittle   a 'glass transition' when too cold and shatter if moved before heating up.
    ' heavy duty' cables are those that should survive abrasion and collision the best, 'light duty' is for environs more like indoors, clean, stable temperatures and  any handling there is not too rough.
    medium is just everything else.
    The regs are really saying 'consider these factors' when selecting your cable, as there is no single 'best answer' for all situations.

    Not a clear cut yes no answer but maybe helps paint the picture.
    Mike.

  • Since I don't have BS EN 50565-01 to understand real definition on described on Light, Ordinary, Heavy duty type. Grateful if you can help on same as well.

    Heavy duty describes the stresses that might be expected in, for example, industrial and agricultural premises

    Ordinary duty describes the stresses that might be expected in, for example, domestic, commercial and light industrial applications.

    Light duty applications might include flexible cables for small appliances

    Extra light duty applications are, for example, very small appliances, for example electric shavers, chargers for mobile phones, etc.