I would agree totally with the other reviewer, it is a great book to have near you for simple yet professional advice. It is written by an electrician and no some boffin just out of university, which explains in both diagrammatic and text format, also on many pages there are highlighted red text explaining myths about different situations i.e. "you must fit a spur units above work tops to supply under cupboard sockets"
I will leave you purchase this excellent book to find out the answer on page 34.
I have just pasted my 17th Edition and starting a new venture in this profession, with about another dozen other books for reference. But this book is possible amongst the top of my list for easy of use and understanding. It relates to all the items you might encounter on the job from installation, through to testing and recording, joining a self-cert scheme, certification, special locations, and all the other stuff, all in good old layman's terminology.
My advice to you when this is available I wouldn't hesitate to order it, as it is very popular judging by it being out of stock so quickly!!
Many thanks to Alan Lynch for some good old fashion easy to read helpful literature.
Cheers
gadgetman