UV protection query for earth cables


I'm seeking confirmation if there is a reasonable engineering response to avoid the requirement for the installation of metal covers as UV protection for large G/Y CPC cables that are installed for external generators and transformers on a metal cable rack system. The cables are 400 sq mm 6491B H07Z-R, and do not have inherent UV protection in the sheath (the accompanying phase conductors do). External portion of cable route is approximately 40m with lots of bends and would be difficult to retrofit with protective covers. I understand there is a requirement to provide UV protection to cables exposed to sunlight, however I would question if there is an argument to claim that the lack of such protection on these large cables would not pose any degradation of their functionality as protective conductors, and that compliance with the regulation in this case would not be reasonably practicable?

  • In the past I think others have argued that in locations like this, where bare copper is acceptable for earthing, while it looks a bit rubbish for the insulation to flake off after a decade or two, it is not actually a problem. Any where it would matter can be taped or painted. at 400mmsq I cannot see there being a corrosion risk of hte cable snapping ;-)


  • Thank you Mike, just have to convince the consultant eng for a very particular Client!

  • Just to add that sometimes the insulating properties of G/Y is needed - e.g. to keep LV and HV earths separated on a "hot" transformer site or simply to keep earthing systems out of touching distance of each other. But as Mike says, if the situation is such that a bare conductor would be acceptable, the G/Y is pretty much just cosmetic.

       - Andy.

  • Thanks Andy

    This is a post installation "snag" so the G/Y sheath is already a done deal. This is one of those times when I'm hoping to convince the EOR to take a common sense approach and perhaps lean on the interpretation of the word "significant" in reg 522.11 to allow a relaxation of absolute compliance. It has been estimated that the total average annual direct normal irradiation in this area is approximately 1000 hours; is it reasonable or correct to class this as "significant"?.

  • if anyone is that worried they can schedule a shorter re-inspection cycle.
    In my experience in most of the UK outdoors wiring the layers of dead leaves lichen and general grot serve as an adequate UV screen in many cases, and in the other half it is in the shadow of something else - I assume this is most unfortunately on the unobstructed south facing side of something without a fence to offer any shade ;-)


  • You could always paint them with a suitable varnish.  That would block the UV.  A bit unconventional perhaps but would meet the letter. I imagine you could get a service life of 10+ years from a decent coating.

  • My interpretation of 522.11.1 requires the wiring must be of a suitable type or shielded when exposed to significant solar radiation or a medium level (AN2) of solar irradiance, which ranges from 500 W/m2 to 700 W/m2. Nevertheless, protective conductors exceeding 6 mm in cross-sectional area do not need covering as per regulations 543.3.201. So does it really matter if the insulation is degraded? 

  • Another way of looking at this is to consider that the earth cables are presumably connected to the bare metal cable tray or racking.