Thanks for your help! I have taken your advice and found a suitable rotary switch and was also able to find a small mcb that may or may not be necessary. I had seen that 16A outlets can be protected by a 20A fuse, which seems crazy as it is not unusual to see power tools etc with 0.75 cable on with no fuses in the plugs this seems a bit of a weird approach. But the regs are the regs!
With respect to my wider question, for future reference if I am making alterations in electrical panels replacing components etc it has just highlighted the need for me to clear things up a little.
Do the regulations in BS7671 only apply to supply installations, obviously when designing wiring inside an electrical panel etc you would try to select cables according to their expected load its just that do you need to rate components and cables inside a panel to the size of the breaker that protects them without exception?
To clarify things i will give you a couple of examples these are not specific examples but just highlight my point
Installing a relay in a panel with its coil wired in parallel across an incoming supply cable. the relay being used to drive a light that indicates the presence of supply. The supply cables may be say 6mm so protected b say a 32A breaker, do the coil connections of the relay need to be as big so that they are adequately protected or is this overkill
A phase rotation relay as above connected in line with the main phases, do the sensing cables need to be fused ?
A proximity connected into a control circuit protected by a 4A breaker with a rated switching current of 200mA
I hope from these questions you can see what i am trying to establish, its not something i have thought about much before. I am sure i have come across installations where situations similar to that described above exist.
what is the common practise?