its been a long time since i did 3 phase calculations so need to do some research again. Basically a school cookery room requires 10 x electric hobs rated at 7kW each and 10 x electric ovens rated at 3 kW each . 3 phase supply Am i wasting my time in even trying to calculate if a 3 phase distribution board can handle this amount of power ?

You could have some interesting diversity calculations or thoughts on that one! As all the pupils will be following the same recipe, when one oven is turned on, so will the other nine. Same with the hobs - and at times you may find that every hob is running at 50% or more and all oven are on full.

Diversity is only allowable on domestic cookers in a domestic setting. This is easy, 70 + 30 = 100 Kw divide by 3 gives 33, 3 Kw per phase and at 230V that will be 145A per phase or at 240V it will be 139A per phase. Good luck!