Luke,
we are going deep on this one, its difficult because i dont know the full circuimsatances (and context) of the question
I will try and expand on what i have already said
Your calculations are a bit off
"the current (I2) causing effective operation of the protective device devices does not exceed 1.45 times the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit"
My interpretation: if you were using singles (for example) and worked out your Iz such that you needed 1.5mm conductors, and you happened to have 2.5mm phase and 1.5mm neutral, then your calcs would be based on the 1.5mm as the "lowest of the current carrying capacities"
Lets say lighting circuit. Ib = 3A (for example)
MCB = 6A so In greater then/ equal to Ib.
Iz for tw/e method 1 =16A
So Ib In Iz is satisfied
Now look at the statement
"the current (I2) causing effective operation of the protective device devices does not exceed 1.45 times the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit"
So 1.45 x Iz = 1.45 x 16 = 23.2A
So the current causing operation of the MCB should not exceed 23.2A
Type B 60898 has instanteneuos trip current of 3 to 5 x In = 3 to 5 x 6A = 18 - 30A
18 is less than 23.2 so its ok.
But it doesnt matter because :
433-02-01
(ii) its nominal current or current setting (In) does not exceed the lowest of the current carrying capacities (Iz) of any conductors of the circuit, and
(iii) the current (I2) causing effective operation of the protective device devices does not exceed 1.45 times the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit"
and 433-02-02 says
"where the device is a fuse.....60898......etc compliance with (ii) also results in compliance with condition (iii)
So basically dude they have worked it out for you! This is why this is a grey area which people tend not to refer to: if you have followed Ib In Iz and you are using a standard protective device then I2 (and so 433-02-01 (iii)) doesnt really ever come into it!
You are either now happy
or in a worse state of confusion than when you started
and my typing hand is hurting
have fun!!!