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exposed conductive parts, again
Question
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."

 
7 Replies
Well you are probably correct, and I would tend to do the same. However, someone will come later and find fault! The various BS's say that sheathed cables may be considered class 2, and if the lampholder is plastic I would be quite happy. There is no chance of significant failure, but if the lamp gets filled with water the situation may change. Tricky one really, and down to experience and drain holes!
`I would say under SINGLE fault conditions. David's suggestion of 'if it fills with water' is a valid one. I'd earth it, but then I am old school and used to TN-S supplies.
Yes, adding the earthing wont harm in this case but it turns out [surprisingly one might feel] it isn't required according to any BS7671 safety issue as it presents even being all metal cased etc - all cable is insulated and sheathed and all connections contained with the lamp holder all plastic...unless I've missed a Reg or mis-read one.

Realistically it cannot fill with water.

That professional elec extract caused me to pause too, with its "... in order for a tray/ladder* to be an exposed conductive part...it must be used as a protective conductor..."    until I went back to read the Regs.

*or any metallic containment/casing one could conclude

Cheers.  Thanks for the comments.
wallywombat
261 Posts
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.
There has been a reply posted by John Peckham, but it is not showing up on the thread at my end.


email received informing "Posted on 16 September, 2020 at 12:40 Europe/London"

Can anyone else see it ?  Has it been deleted since ?  
-2400-
79 Posts
Hi, if it helps - I can't see it.
It appears it was removed/deleted after posting for some reason, that explains why it is not in the thread...even though I received the email alert with the post etc.

Perhaps John Peckham will repost if the 'delete' was made in error ?!

Cheers

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