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However the next statement is what I am raising here, the need for a Type A RCD, looking at Screwfix web site a page of 16 RCD's all are Type AC so would not comply, the RCD fuse connection unit does not say what type other than active or passive, only the RCBO's seemed to comply most being Type B and some Type C.
So it would seem only way to comply would be to use a dedicate circuit from a RCBO in which case why have a fuse, except it says 3A fuse on next arrow point.
Ideal
Yes I know one uses a bit of common sense, but as soon as you don't comply with one manufacturers requirement then why follow any, it does say "practicable" but when wiring a new build it would be "practicable" so would one have to fit a RCBO and a FCU and interconnecting wiring between the heating control and the boiler.
The central heating was always the most complex wiring in a house, with the introduction of combi boilers it made life easy, all the complex wiring was inside the boiler, and controls went analogue, however Part L building regulations messed up that, so we now have zones, it seems no one has really defined what needs to be controlled in each zones, some government publications seems to say using TRV in every room is enough, others want time controls as well, again easy way is the programmable TRV but they are normally battery powered, so then not all supplied from same source, my house has 10 sources, 9 x twin AA batteries and one 230 volt FCU.
So if you are designing the wiring for a home, assuming once complete some other tradesman will fit central heating, what should be provided for the heating engineer to install the heating and ventilation and if appropriate cooling devices? My old house the supply to Myson fan assisted radiator is completely independent to boiler, as the water gets hot the thermostat turns on the fan, and the fan is also controlled by the temperature of incoming air, I really see no good reason why the radiator should come from the same plug as supplies the boiler.
Be it a motorised on/off valve, or a motorised analogue valve (TRV), pump, or fan assisted radiator I see nothing in BS7671 to say all should be from same plug or FCU, it is only the manufacturers who seem to want all from one FCU/Plug. From what I am lead to understand we no longer need to follow manufacturers instructions.
So what is reasonable, what is required, what is sensible, what would you do etc?