Are breaker curves different in the UK? I though D curve breakers were specifically for high inrush inductive loads. A D32 breaker shouldn't trip until inrush hits at least 320A, well above what a 22kw star-delta should draw on startup.
It's a little bit more complex than that, the starting duty of a motor has to be take into account as the tripping curve also has a time value to it, it is therefore a reason we would need a 63(D) in the 22kw example and this wouldn't suit every occasion, high inertia loads need extra allowance and more than likely would need a MCCB or HRC fuse suited to the longer start up duty.
Schneider own tables recommend a 50(D) MCB for a standard duty star/delta 22Kw
Hagar own tables recommend a 63(D) for the same.
This hi-lights some operational differences between different manufacturers hence this should be properly designed to ensure no nuisance tripping occurs, this area of design is the one that tends to trip up even the experienced sparks out there who don't delve into power supplies to machineries, more and more of my callouts are domestic/commercial sparks moving into industrial due to competition or lack of work in their own comfort zone and making some costly mistakes, I often utilise a BS7076 clause that allows the overcurrent device to exceed the CCC of the cable it is covering while ensuring ELI tripping times are not contravened, this falls under the fixed load clause which negates the need for overload protection, If I was to match the cable to the protective device rating on half the jobs I do it would be a lot of wasted material costs but I see this all the time when I am called into these factories.
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PS - as I was quoting a 11Kw which somehow became 22Kw (think you mixed amps and KW up and I followed on from it
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The correct tables for a standard duty startup of a 11Kw are
63(B), 63(C) or a 25 (D) as listed by Schneider... noting the 25(D) type and looking at the ELI permitted values it may be the case 'but not always' that a cable is easier to achieve a permitted value by selecting the higher value MCB with a lower trip curve, in this example a 25 (D) would suit and we can allow more room by looking at the 5second trip figures as oppose to 0.4 values but that depends on the machine and its power circuits if we can allow that.
If ever in doubt its best to go with the C type value and design to that IE the 63(c) for an 11kw, weighing up the duty of a motor on startup is not always possible especially when info is lacking, this is where experience comes in, but as you can appreciate this goes well beyond of the OP if he was to come across this situation.
