In the bathroom you are supposed (as I understand it) to have secondary electrical bonding of all exposed metal parts like taps and metal shaver socket fronts. But does this rule apply to the chrome plated metal strips that I will have up the edges of my tiled areas when the work is done? These edge strips will present 10mm wide metal surface running from floor to ceiling. Two will be touchable when lying in the bath.
It would be a pain in the neck to have to connect an earth bond to them - but to retrofit it would be worse!
On 17 May 2007 02:04:41 -0700 someone who may be Robert Laws wrote this:-
If they are liable to introduce a potential into the zone. Taps are liable to do so, if they are connected to metal pipes which run elsewhere. A metal shaver socket front is an exposed conductive part and thus must be bonded as it is liable to introduce a potential if the socket fails in some way.
Are they liable to introduce a potential? Are they connected to anything outside the zone? The answer is probably no and therefore they do not need to be bonded.
Don't worry about it. If it comes to fruition as promised the 17th edition will remove the requirement for supplementary bonding as long as the services have main equipotential bonding in place.
Interesting. Do the people who write these things live in the real world or (conductive) ivory towers? The principle of bonding in a domestic bathroom always struck me as overkill if the basic house wiring and bonding etc was correctly carried out - and unlikely to be done properly if at all where that was bodged in any way.
The whole purpose of equipotential bonding is to mitigate the danger when there *is* a fault. So it is almost by definition overkill when everything else is working ok.
thank yo uall for your help. of course these strips are clearly not connected to anything else (outside the room) so they cannot introduce a potential. I'll relax.
What you say about shaver sockets is the way a sane person would have approached it and does actually meet the regs but they are more relaxed:
Electrician's Guide to the Building Regulations - see 5.3.1 "A supplementary bonding conductor needs to be run to the protective conductor of the circuits supplying the fixed equipment to include the equipment within the supplimentary bonding of the bathroom. There is no need for the supplementary bond to be fixed directly to the piece of equipment." Fig 5.3a note 2: "Circuit protective conductors may be used as supplementary bonding conductors."
It is clarified in an interesting IEE document - google for 'section 601 revisited' and click on IEE wiring matters 2005.
In short, we seem to be required to put a wire between exposed metal bits and a connecting screw in a probably already crowded switch or junction box just next to live parts. Not sure which is worse - this one or swapping blue and black over in 3 phase wiring.
As for the OP's question about those metal strips, 'Accessible metal structural parts of the building' are included in the list of things which need bonding but these strips are not structural. I hope that also applies to the individual links on the bathplug chain!
On Sat, 19 May 2007 00:02:18 +0100, Andy Wade mused:
I was going to post something along those lines but not being 100% sure on the upcoming 17th edition RCD\no bonding rules I decided that you'd be along to clear it up at some point. ;)
Thought the general consensus here was that RCD protected lighting circuits weren't a good idea? Or does this just refer to a whole house or shared RCD?
The whole house RCD idea is certainly deprecated, but that is mainly because of its lack of discrimination, along with its tendency to sensitise the RCD with too much legitimate leakage.
This is a new special case that is unlikely to have those problems, and where I guess they feel that the advantages outweigh any slight increased risk (i.e. you may lose lights, but chances are the landing light is on, so opening the door will let you see again), and the proposed solution is likely to cause less confusion than the current situation which an awful lot of people seem to have difficulty getting their heads round.
In practice I think it will depend a little on how installers set about implementing the new rules. With a bit of thought it would be easy enough to mitigate the negative effects. Most installs with have a split load CU with all the socket circuits protected (and hence any miscellaneous power that is likely to he used in the bathroom). Electric showers etc frequently seem to get RCD protected even when earth fault loop impedance does not actually dictate this. So addition of a dedicated lighting radial for the bathroom from a RCCB on the non RCD protected side of the CU would maintain the discrimination while providing the required protection. (This assumes the rules don't insist that the same RCD protects all the bathroom circuits).
Sheesh, that's a thought. I wrap our bath plug chain around the tap to keep it out the way during a shower! Note to self: handle by rubber plug only in future ;-)
On Sat, 19 May 2007 11:34:11 +0100, "Dave Plowman (News)" mused:
I'd probably not stick the whole upstairs lighting on an RCD just to overcome the lack of bonding in a bathroom, I'd be more likely to use an RCD spur for the bathroom lights then it can be fed from the upstairs lighting circuit and be tidily fitted.
Other option is to run a seperate feed from the CU for the bathroom lights, but I can only see the RCD for lighting in the bathrrom being used on retrofit applications to bring an installation up to scratch so this would probably be as much of a job as fitting the correct bonding. If it was a new install then I would imagine non RCD lighting and bonding would still be the norm.
That wouldn't comply. Unless anything changes, RCD protection will be mandatory for all bathroom circuits [Reg. 701.411.3.3 in the public draft of BS 7671:2008]
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