Doc 53

Not correct I am afraid. You also need to account for earth fault loop impedance and its effect on tripping times and co-ordination between breakers. The best method for understanding cable calculations is spreadsheets, Microsoft office being the most used (although the stuff on Linux that is free is just as good). In the real world full sequence for cable sizing should be: - max demand for DB (using AS 3000 is fine for basic sites, custom calculation is required for complex projects. The later allows the use of diversities to establish load profiles between major load groups). You need to make sure here motor inrush etc to co-ordinate with breaker setting. - dearate cables for ambient temperature, installation method, grouping of load carrying circuits and cable type. - apply cable length to confirm volt drop - apply cable length to calculate adult level at end of cable. Use this value to establish tripping within AS3000 rules, and protection co-ordintates. At this point you may need to use a larger breaker than the required load, to achieve co-ordination/discrimination. This may result in larger cables being required. - confirm cable size meets requirement of the a diabetic equation for withstand of temperature rise during fault condition, at origin of cable. Sound familiar? It should, AS 3008 (cable selection) directly aligns with IEC60364 (international standard for electrical installation in buildings) which also aligns with BSEN7671 (requirements for Electrical installations). unsurprisingly any major installations will be carried out in computer software like powercad/cable calc/powerpak. Be warned all have short comings!