It just seems to me that if BS7671 is to contain regulations which apply to "Consumer Units", and if the Building Regulations are to contain (notification) requirements which apply to "Consumer Units", then it really should be incumbent on the authors of both of those documents to provide very clear and easy-to-understand definitions of what they mean by "Consumer Unit" in relation to their requirements - just as, for example, the authors of BS7671 should also provide a clear definition of "non-combustible" and the authors of the Building Regulations should also provide a clear definition of "a new circuit".
For comparison, look at how for the purposes of defining whether or not some job is notifiable, the Building Regulations refer to BS7671 for the definition of a special location (do they still say BS7671:2001, or has that now been updated to 2008?). If the Building Regulations had used the term without such a reference, it could be taken to mean almost anything.
Given that whether something is or is not a consumer unit can similarly affect whether or not a particular job is notifiable, one might think that they would have included a specific definition or a reference to some other document in which it is defined, as with "special location."
I fear its far from being as simple as that. The "reasonable man" might well say that a circuit was 'new' if one had replaced every component (OPD, cables and accessories) of a pre-existing circuit - but many (or most) people would probably regard that as non-notifiable. Similarly if a house-wide multi-socket circuit was added to what started as one socket (or even JB) connected by a few inches of cable to an OPD in a CU. Conversely, he might well say that a circuit was 'not new' just because the OPD had been changed to one of a different (but appropriate) rating - but at least some would say that constitutes creation of a 'new circuit'.
Indeed. I think the general interpretation most people have put on it is that if there's already a fuse or MCB feeding
something, then you can add or change anything you like which is fed from that fuse/MCB without creating a new circuit, even if the original circuit was 2 feet of cable to a single socket and you extend it all around the house. But without a specific definition of "new circuit," there's still room for argument about what it actually means.
There are at least some, even in this forum, who believe that 'changing the characteristics of a circuit' by changing the OPD to one of a different In constitutes creation of a new circuit.
Extending an existing branch circuit (adding on to a radial, inserting extra cable and sockets on a ring etc.) is changing the characteristics of the circuit too (different loop impedance etc.), but would they regard that as creating a new circuit? If so, then it would preclude making almost
any changes without notification!
In the earlier set of regulations for notification there was the language about "where circuit protective characteristics are not affected" or something similar, and I know that seemed to cause a lot of confusion too, because it was written in such a way that the condition applied to certain jobs but not others. Some people tried incorrectly to include that for
all work.
... and is the "reasonable man" being unreasonable by believing that replacing every component of a circuit renders it a 'new circuit'? .... Indeed. But if you 'replaced' all the wool (or whatever), he might well regard it as a 'new sock', just as if you replaced the cable, accessories and OPD of a final circuit.
It's not straightforward, even for the "reasonable man"!
And if we're talking about what seems reasonable to the reasonable man, how would he feel about it being notifiable to run completely new wiring and sockets around the house and connect to a newly installed MCB, but it being non-notifiable to disconnect and remove all the old wiring from an MCB, then run his new wiring and connect to the existing MCB?
