no john i dont believe having an earthed conductor in the cable is wrong at all. it`s probably my fault for lack of clarity. having (example on a lighting circuit) earthed fittings on a SELV system would be wrong
2 core 1.5mm on lights.
- Thread starter Nugget75
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Yes ,I got the impression that we must have been 'talking at cross-purposes', but I don't think I could be criticised too much for interpreting your ...
... in the way I did!
Sure, but that's rather different, since you are now talking about connecting 'earth' to a SELV fitting (which, apart from anything else, would achieve nothing - other than increasing the amount of 'earthed metal' around, hence theoretically increased risk of shocks!). Having earthed armour within the SELV cable which is not connected to anything else (in the SELV system) is obviously different and, as I have suggested, presumably 'OK'.
Having said that, I'm not sure that there would even actually be anything 'wrong' with earthing 'exposed-c-ps' of a fitting supplied by SELV. As above, it would achieve nothing positive but, provided it was not connected to either side of the SELV supply, I can't see why it should be an issue.
Kind Regards, John
Is it correct to even call the conductor/part in question "earth" as far as the SELV object is concerned?
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As far as terminology is concerned, I would say that "earth" (which usually means the "installation's earthing system") is 'earth', regardless of anything else.
What I think you probably mean, with which I would agree, is that the concept of 'earth' is of no relevance to a supply/system (such as SELV) which is not earth-referenced. In the eyes of such a system, the fact that something (to which it is not connected) is 'at earth potential' is not really any more relevant than, say, if the something were at a potential of 1,000V above earth potential.
I suppose it's in some senses similar to the argument (as in many MIs) that touchable metal parts of a Class II item "must not be earthed". From the point-of-view of the item, it doesn't make a blind bit of difference as to whether those metal parts (separated from anything that matters by "double or reinforced insulation") is 'earthed' or not. The only downsides of earthing that metal is that it unnecessarily increases the amount of 'touchable earthed metal' in the building (hence theoretically increasing shock risk) - but that would be equally true if one were talking about 'earthing' metal door knobs or window frames.
Kind Regards, John
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