Division of installation requires that every installation shall be divided into circuits, as necessary, to:
- avoid hazards and minimize inconvenience in the event of a fault
- facilitate safe inspection, testing and maintenance
- take account of danger that may arise from the failure of a single circuit such as a lighting circuit
- reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
Let's take a CU change on an existing installation in a flat with the following circuits:
- 1 x 32A cooker circuit
- 1 x 32A ring main
- 1 x 20A socket circuit covering part of kitchen
- 1 x 6A lighting circuit
It's easy to minimise inconvenience and reduce unwanted RCD trips either by splitting the circuits across two RCDs or by a full RCBO setup.
However, single lighting circuits are generally frowned upon due to the potential danger of losing all lighting within the property. How does one resolve this?
- Putting the lighting on a seperate RCD to the ring main, for example, would presumably reduce unwanted RCD trips taking out the lighting
- Putting the lighting on an RCBO would achieve this potentially to a greater extent
My personal opinion is that the installation will be "no less safe" than it was prior to the CU change, therefore would be acceptable. But ultimately, the lighting is still a single circuit which does not fully meet this requirement of BS 7671?
What are your thoughts?