by ericmark »
Wed Oct 31, 2012 11:17 pm
I will guess it is RCD not MCB. The question is what was the requirement when it was installed. I do find this is a problem as I only carry the current regulations. There have been some major changes through the years.
I may have years wrong but some where around 1968 there was a major change where lighting circuits required earthing. That would have been the FOURTEENTH EDITION of the regulations.
In 1992 the SIXTEENTH EDITION became BS 7671:1992 and since we normally refer to the BS number although the first edition came out in 1882 in real terms the furthest we go back is 1992 as being the previous edition.
We are now on the 17th Edition amendment 1 although I only have a copy of the 17th Edition which is also called BS7671:2008. There were some major changes when this came out and also some clarification the latter if anything was more of a problem. Very early in the book it states:-
314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
Sounded nearly the same as the old book but it clarified that having a single RCD on all circuits would not comply and there was a mad dash to produce consumer units which could support multi RCD protection.
The RCD featured heavy in the 17th with 522.6.5 dealing with cable protection and 415.1.1 saying what RCD was required and what required protection. Sockets under 20A with some exceptions now need RCD protection not just sockets feeding outside. Bathroom lights now need in the main RCD protection so combine that with the regulations on buried cable near all new circuits now need RCD protection.
Although in the main the consumer unit is where this is added the rules don't rule out other methods. For example extending a ring final circuit with Ali-tube cable to BS 8436 and using RCD sockets would fully comply with the regulations. Although at the price of RCD sockets I would not want to install too many using that method.
The point which is made many times is the only person who can sign the installation certificate is the person doing the work. There are two forms one with a single signature and one with three signatures. With the latter design, installation and inspection and testing have room for signatures so your son would sign the first two and the electrician would sign the last bit. However the electrician can't use his membership of a scheme when using three signature forms he would for notifiable work need to submit it to the LABC. The forms are a free download from the IET website.
He can of course do his own testing and inspecting there is no rule to say what qualifications are required. We would normally consider a C&G2392 or C&G2391 would be held by the guy signing but there are no rules to say you must have passed that exam. The LABC however can decide if it thinks the person doing the work has the skill and often the C&G2382 which shows one can read the regulations book is enough for them. Clearly electricians from other EEC countries can work here and so there are a host of qualifications including never taking any exam but just doing an apprenticeship.
So replacing an orignal double socket back box with a twin back box housing two FCU's one with RCD combined and the other with 3A fuse for lights using a spur system to feed the new sockets and lights would likely comply with the regulations. However to fit RCD's on a ring final circuit would either mean RCD sockets or a RCD at the origin. There would be nothing to stop one taking the supply from the 32A fuse to a separate RCD before it feeds the ring however cost wise likely it would cost less to buy a whole consumer unit rather than mess around with multi boxes to do the same thing.
Where the problem arises is changing a consumer unit is notifiable work. I have read and re-read the Part P regulations and it would seem it was written by non technical staff as technically using a FCU produces a new circuit reading the BS7671 definitions yet it seems under Part P these are not considered as new circuits. Even the wording "ring final circuit" does not make sense as when one adds a FCU then clearly it's no longer the final circuit. So some interpretation is required and of course some will decide it means something different to others so there is only one way and that is read the regulations yourself.
