Wired the air con with 2.5 flex and 20a type C. Works fine.
Who ever does their specs want shooting. Over estimated. Probz because it's not their money it's the tax payers.
Floating on the same lines as Lucien here ....
When speccing a cable type and mcb rating for motors - things to be taken into account:-
-The frequency of start
-The duration of the start
-Your calculated ELI relative to you mcb type meeting the starting current without tripping
The first 2 points are relatively rare in the domestic and small commercial to be an issue but as in my area of work is crucial as the larger high inertia motor loads take some extra considerations when designing.
The manufacturers instructions now should specify a mcb rating to protect their product like in OP's case and this may specify a 32(b) for a number of reasons, manufacturers tend to play extra safe and can over-spec products requirements to account for worse case scenario's because they lack many neccessary info to give a better guidence.
Having said that if this is a dedicated circuit then protecting the cable for O/L may not be required as the unit should have O/L protection for the motor and thus could be classed as a fixed load circuit meaning you may be able to keep say a 32a(b) if requested by the manufacturer but only supply it on a 2.5mm cable (installation calcs allowing of course).
Manufacturers sometimes use the term 'recommended' mcb rating and this is just that 'a recommendation' - if you can calculate it diferently and prove the lower rating won't nuisance trip then do so but if on the rare occasion you are asked to justify your calcs then be prepared to do so.
To note here and a trap often fallen into is the trip curves of mcb's
Example lets say a 10amp type C has a tripping characteristics of 5ln - 10ln and your motor has a 6amp flc but a peak inrush of 55amps which is 5.5ln relative to this mcb, now the mcb can trip with a current anywhere between 50a and 100a, any higher than 100amp inrush should trip it 100% of the time but when you get close to it lower limit the frequency of tripping here become very low. Having said this if it can trip at all and your inrush falls within the range then you should either increase the mcb type of the mcb ampage until the chances of inrush tripping is 0%. Not forgetting to still meet ELI and VD.
Your peak inrush should be lower than the lowest trip 'ln' of the mcb many think that if you inrush is within the 2 'ln' values of the mcb then this is ok.... the mcb does not trip at a certain ampage repeatedly, you are given the lower and upper tolerances of the mcb and it may trip at 51 amps on one occasion but next time it may trip at 99amps (in relation to my example).
