OP
Outspoken
I will agree to disagree here, when using mcb's on motor circuits manufactures guidelines must be referred to to ensure nuisance tripping is not ever going to be an issue due to inrush.... and with said compressor been a fixed load and as long as you dont fit it as a plug and socket arrangement the the cabling can be wired as per load and cable calcs and the mcb can overrate the ccc of the cable meaning no additional costings and would still fall within the BS7671.... the number of times ive corrected others installs because the mcb's are nuisance tripping because they stuck basic calcs and believing that the mcb only need be rated the next size up and typed as a (c) in the case of a motor. It dosn't work like this as the trip threshold of the next size up mcb is often too low regardless of type fitted....this is especially the case with compressors as they start on load.
And do you know how many motor installs I have done in the last 32 years...I work with motors continually, and most a lot higher rated than 5.6kW and I have never had any issues with using Type C or D MCB's when the calcs have been done with accurate information. I am used to dealing with motors that start under load that make the 5.6 spoken of seem like the piggy back starter. Your also likely forgetting that at this rating I would think the starter will be YΔ. As for your satisfaction of over-rating the CC of the cable..on that we will have to disagree because I will never agree with that being satisfactory or acceptable.