Hi
I used the 40% of the overcurrent method, as this method in my experience comes closer than the osg diversity factors in flats and small houses. Lets say the house was three bedrooms plus I would revert to the osg rules as I think these would be closer to figure. More often than not connected single loads on maximum run on 50 to 70% of there rated loads.
Andekoch just brought up the circuit division as more domestic properties have failed on this, ten fold than they have on maximum demand one year on for the 17th edition meeting in London.
I know this method I have used might not sit well with everyone what do you guys think.
I agree with Electro (and the other comments) the calculation should be done as per a standard method eg the OSG and the result interpereted (this is where experience come into the picture). The type of proprety will also make a difference (same reason that the OSG has different diversity tables for houses, shops etc).
You should clearly note how you arrived at your decision and not simply write max demand = 119A on the installation form and then install a 100A main switch.