Will be the similar to the one we do at the boat people course i believe. There is a large section at the back of the regs book about maximum demand and it tells you the load values for each item group which you split across the 3 phases in to circuits and then you get the total load and select the smallest mains cable you can get away with allowing for volt drop ( yes really must be an ozzie thing!! I would have been struck off for that in the UK!) Pretty straightforward stuff really and pretty much the same as the UK.
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!
Maximum Demand project assignment electrical contractors licence
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Posted · Edited by 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!