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exposed conductive parts, again

psychicwarrior
From reading previous topics and guides somewhat (see one example below), it would seem cable tray/ladder etc is considered not an exposed conductive part. One could conclude also, that so long as there are no unsheathed/protected cables in metallic containment, then that containment would not be classed as exposed either.


Indeed, inside a metal encased piece of equipment, if all the wiring is insulated and sheathed, then the metallic case need not be earthed.


This might explain why I found no earthing on an old converted metallic cased outdoor [coach style] light (a large one) or its beefy cast iron/steel bracket through which the cable ran, as all the cable to the light and inside it was insulated and sheathed with no unprotected conductors on show.


It does appear to be a compliant install with regard to BS7671 and therefore is safe for continued use, so adding the earth (as I initially wondered given all the conductive metal etc)  would have been uneccessary.


Any other views/comments from experience appreciated on the above observations ?


e.g. extract from

https://professional-electrician.com/technical/bonding-time/


 

Exposed-conductive-part



This is a conductive part of equipment which can be touched and isn’t normally live, though it may become live under fault conditions.



Conclusion



In order for the tray/ladder to be an exposed-conductive-part, and therefore require earthing, it must be used as a

protective conductor as per the requirements of BS 7671:2008 Regulation 543.2.1.



 


If the tray/ladder is carrying sheathed and/or armoured cables (which it most likely will be) then the nature of that type of cabling suggests that the tray/ladder won’t require earthing as the cable has adequate mechanical protection i.e. more than just basic insulation. This meets the requirement of Regulation 412.2.4.1 and therefore the tray/ladder doesn’t need earthing."


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    It is sometimes argued that earthing something like ladder/tray unnecessarily can be harmful, since during a fault but before ADS has kicked in, there are now more things for people to touch which are at a potentially dangerous potential. Personally I'd argue the other way round - there's a potential for e.g. burrs and other constructional defects to pierce both the sheath and insulation of a cable, making the tray potentially live during initial energising. I think you have to toss up which of these two scenarios is more unlikely.
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  • 0
    It is sometimes argued that earthing something like ladder/tray unnecessarily can be harmful, since during a fault but before ADS has kicked in, there are now more things for people to touch which are at a potentially dangerous potential. Personally I'd argue the other way round - there's a potential for e.g. burrs and other constructional defects to pierce both the sheath and insulation of a cable, making the tray potentially live during initial energising. I think you have to toss up which of these two scenarios is more unlikely.
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