How to Calculate the cable size and protective device rating

Electrical Installation Design This is an older video. New video coming soon to clear this up The term 'Iz' has been incorrectly used when it should be 'It'' The calculation method is still correct, however. 'It' is the value we find in BS7671 appendix 4 after we carry out out correction factor calculation. The calculated value I have since discovered, has no name. From BS76712 This method is used in items 5.1 and 5.2 and produces a value of current and that value (or the next larger value) can be readily located in the appropriate table of current-carrying capacity and the corresponding cross-sectional area of conductor can be identified directly. It should be noted that the value of It appearing against the chosen cross-sectional area is not Iz. It is not necessary to know Iz where the size of conductor is chosen by this method. All rating factors affecting Iz (i.e. for factors for ambient temperature, grouping and thermal insulation) can, if desired, be applied to the values of It as multipliers. This involves a process of trial and error until a cross-sectional area is reached so that Iz is not less than Ib and not less than In of any protective device it is intended to select. I n any event, if a rating factor for protection by a semi-enclosed fuse is necessary, this has to be applied to In as a divisor. It is therefore more convenient to apply all the rating factors to In as divisors. This method is used in items 5.1 and 5.2 and produces a value of current and that value (or the next larger value) can be readily located in the appropriate table of current-carrying capacity and the corresponding cross-sectional area of conductor can be identified directly. It should be noted that the value of It appearing against the chosen cross-sectional area is not Iz. It is not necessary to know Iz where the size of conductor is chosen by this method. How to carry out cable calculations to correctly size your electrical conductors Design Current Protective devices Current carrying capacity Volt drop Sizing of the MCB/Fuse and more... At 21.29 you might spot I used the In instead of Ib in the volt drop calculation. So 16A instead of 13.04 A Volt drop is actually 13.23v not 16.24v Still unsuitable cable though 22.16 Maths error Ib x L