Although related to the current ‘cross bonding’ thread, I’ve spun this off into a separate thread, since it’s essentially a separate and circumscribed issue.
The issue of earthing/bonding seems to take on new dimensions when one gets outdoors – e.g. sockets in gardens, greenhouses and sheds etc. Short of ensuring that there are no exposed-conductive-parts and trying to ensure that only Class II equipment will be powered from such sockets, I’m not really clear as to what one can or should do about protection (apart from ensuring that the circuits are RCD-protected). Effective ‘bonding’ of the wet walls of a timber shed or all of the soil in a garden is clearly not a viable option!
A little while ago, I saw a socket which had recently been installed (by an electrician) in a friend’s greenhouse (metal framed, with the metal frame sitting on/attached to a low brick wall) and noticed a G/Y cable connecting the socket to the frame of the greenhouse. In common sense terms, that struck me as being not-too-clever an idea, primarily because it means that someone could be touching the metal frame whilst standing on the ground (potentially with bare feet!). In the absence of any ‘bonding’ between frame and soil, that could obviously represent a hazard under some fault conditions. In effect, the electrician had turned the greenhouse frame into a giant exposed-conductive-part, with an ('unbonded') path to true earth nearby.
There is also the issue that if the greenhouse’s frame had some meaningful degree of connection to the soil (e.g. wet bricks), the SWA’s armour (and CPC if it had one) would be introducing another variant of ‘earth potential’ into the house’s electrical installation. However, I suppose that's no worse than having bonded water supply pipes. ‘Earthing’ the greenhouse frame to a local electrode would enhance that problem, if the G/Y cable remained in place.
I suppose that one solution would be to not connect the SWA’s armour/CPC at the greenhouse end but, instead, to connect the socket to a local earth electrode and ‘bond’ this to the greenhouse frame - i.e. create a local TT installation.
When it comes to ‘garden sockets’ (i.e. not in a greenhouse/shed etc.) the problems would seem to be essentially insuperable, so I suspect that reliance on use of Class II equipment is about the best one can do (apart from the RCD protection).
Any comments, or help in understanding how these situations are usually dealt with?
Kind Regards, John.
The issue of earthing/bonding seems to take on new dimensions when one gets outdoors – e.g. sockets in gardens, greenhouses and sheds etc. Short of ensuring that there are no exposed-conductive-parts and trying to ensure that only Class II equipment will be powered from such sockets, I’m not really clear as to what one can or should do about protection (apart from ensuring that the circuits are RCD-protected). Effective ‘bonding’ of the wet walls of a timber shed or all of the soil in a garden is clearly not a viable option!
A little while ago, I saw a socket which had recently been installed (by an electrician) in a friend’s greenhouse (metal framed, with the metal frame sitting on/attached to a low brick wall) and noticed a G/Y cable connecting the socket to the frame of the greenhouse. In common sense terms, that struck me as being not-too-clever an idea, primarily because it means that someone could be touching the metal frame whilst standing on the ground (potentially with bare feet!). In the absence of any ‘bonding’ between frame and soil, that could obviously represent a hazard under some fault conditions. In effect, the electrician had turned the greenhouse frame into a giant exposed-conductive-part, with an ('unbonded') path to true earth nearby.
There is also the issue that if the greenhouse’s frame had some meaningful degree of connection to the soil (e.g. wet bricks), the SWA’s armour (and CPC if it had one) would be introducing another variant of ‘earth potential’ into the house’s electrical installation. However, I suppose that's no worse than having bonded water supply pipes. ‘Earthing’ the greenhouse frame to a local electrode would enhance that problem, if the G/Y cable remained in place.
I suppose that one solution would be to not connect the SWA’s armour/CPC at the greenhouse end but, instead, to connect the socket to a local earth electrode and ‘bond’ this to the greenhouse frame - i.e. create a local TT installation.
When it comes to ‘garden sockets’ (i.e. not in a greenhouse/shed etc.) the problems would seem to be essentially insuperable, so I suspect that reliance on use of Class II equipment is about the best one can do (apart from the RCD protection).
Any comments, or help in understanding how these situations are usually dealt with?
Kind Regards, John.