Having read all that has gone before, there still seem to be some areas where the interpretation is unclear.
Do pipework bonds have to be both visible and accessible? If simply accessible, do the same sort of conditions governing the use of junction boxes apply (e.g. removable floorboards)? What about under the bath? Is this influenced by whether or not tools are needed for access, or does that only affect the need for bonding?
When connecting to the various CPCs, presumably at existing fittings, or junction boxes (can't quite see 4mm cable being accommodated in a light fitting) is there a requirement for identification somehow?
So far as I can see, it is quite OK for the underfloor bonding and the ceiling bonding to be joined only by a common length of pipe. Is this right?
Yes, unless soldered, welded or crimped, etc. Joints relying on screw terminals should be accessible.
The same rules apply as for live conductors, yes. "Accessible" isn't defined in BS 7671 and is open to interpretation - anything is accessible if you demolish enough of the building! Use common sense - anything requiring destruction or inconvenience out of proportion to the task of accessing the connection isn't compliant, IMO.
That surely affects neither.
Identification of the bonding conductor as a protective colour is by means of the green/yellow colour. The "safety electrical connection - do not remove" label is only required, in this context, at connections to extraneous-conductive-parts (i.e. non-electrical stuff like pipework); it's not required on bonding connections to exposed-conductive-parts or CPCs.
The 4mm^2 size is only needed if there's no mechanical protection. An enclosed bonding conductor on to the CPC of a normal lighting or shaver point circuit can be 1mm^2 (for circuit cables up to 1.5mm^2) - and of course you are allowed to use the CPCs as the bonding, provided that they remain "in close proximity to the [bathroom] location". So on the lighting circuit it's often more practical to bond to the earth terminal in the switch enclosure than in a luminaire.
Debatable. Reg 547-03-04 allows conductive parts "of a permanent and reliable nature" to be used as part of the bonding. If you think a plumber could come along and replace the pipework in question with plastic and not realise that any bonding would need to be patched then, IMO, that regulation couldn't be applied. (IOW, if in doubt, bond separately.)
I am a bit sceptical about this accessibility issue. How many people have mains and lighting connectors under their floorboards, I suspect many of us, and how many have carpets, flooring etc. on top. , so not really accessible. I have heard the arguments about copper creep etc. but over the last 15 years of owning a house I havce never had to rip anything up to find a fault with ring main/lighting circuit. Am I just lucky?
In a sense this is a slight extension of Fig 4d in the OSG - several separate supplementary bonds taken back to the plumbing - which ties everything together. So say your cold riser from underfloor up into the loft _could_ be used as the path to link lighting circuit bonding to the rest, subject to the proviso as above that its unlikely to be replaced without Joe Plumber getting sufficient clue that the bonding was at both ends of it. So if the earth clamps are well away from the vertical run, then not a good idea, but if the clamps are say just above the ceiling at the top, and at say floor level in the airing cupboard, then I wouldn't see a problem.
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