First we must define maximum demand and diversity factor of an electrical installation.
- Maximum demand is the maximum anticipated installation load plus any allowance for future loading (Sm);
- Connected load is the total of all electrical loads (Sc);
- Diversity is the ratio of maximum demand to the connected load (D).
Diversity, therefore, can be represented by
D = Sm/Sc
To provide an economic design which meets the safety requirements needs design experience, skill and not a little judgment in establishing a figure for the actual load (i.e. maximum demand).
In load assessments, certain assumptions have to be made with regard to actual current drawn by equipment. Fixed loads are easy, but this is not so for some other loads for example socket-outlet circuits, which may have a theoretical load many times that which is likely to be drawn in service.
Generally diversity factor of switchgear may be decreased due to number of outgoing increasing. Based on experience, IEC 60439-1 has suggested a ‘diversity factor’ as noted in Table below. This factor depends upon the number of outgoing circuits and is defined by the ratio of the maximum loading on a particular bus section, at any time, to the arithmetic sum of the rated currents of all the outgoing feeders on that section.