by Steve on October 3, 2009

Diversity & Maximum Demand

The ‘nameplate’ rating of an electrical appliance relates to its maximum demand but does not reflect the electricity usage of that appliance over a 24 hour period. For this reason a factor of ‘diversity’ can be allowed.

Diversity can be applied to a circuit because not all of the connected loads are operating at the same time or at their maximum rating.

When calculating maximum demand for an installation allowance for diversity is normally expressed as a percentage of the maximum demand for each circuit.

An electrical distribution system can be broken down into groups of smaller systems or branches, successively connected together forming the whole network or tree.

Each of these branches can contain smaller branches and ultimately, ‘final circuits’ and then individual items of equipment.

(The operating load existing at any location in a system, at a given point in time, is the sum of the loads downstream existing at that point in time).


Larger scale

Diversity calculations are very important in the case of distributing and generating electricity.

Knowledge of demand is vital to regulate the generation of electricity and maintain reliable electricity supplies whilst minimizing environmental impact such as emissions of CO2.


Smaller Scale

It is important to know the total current demand of an installation consisting of a number of ‘final circuits’ to prevent overloading of fuseboards and supply cables.

When calculating the maximum demand to fuseboard in a typical domestic dwelling, the diversity factors by suggested IET (UK) are:


Lighting 66% of total current demand
Heating 100% up to 10amps plus 50% of the remainder
Cooking 100% up to 10amps plus 30% of the remainder (plus 5amps if socket outlet
Water heaters (instant type) 100% of the two largest appliances plus 20% of the remaining appliances
Water heaters(storage type) 100% of total current demand
Floor Warming 100% of total current demand
Thermal storage Space heating 100% of total current demand
Socket outlets 100% of current demand at largest point of demand plus 40% of every other point

The total of the above results will be calculated as ‘amps’.

Note- Maximum loading of most domestic fuseboards (UK) is 80 to 100amps.

To avoid confusion designers must always keep in mind actual operating conditions in an installation and allow for possible future expansion of the installation.

The information given in publications such as the On-Site Guide is intended for guidance only because it is impossible to specify the appropriate allowances for diversity for every type of installation. Special knowledge and experience may be required for a specific installation.


{ 2 comments… read them below or add one }

Odeh justice July 10, 2012 at 06:25

Yr work on electrical installation is very much relieable.

billy bunter October 6, 2009 at 09:15

Thats useful informatin espicaly as I am looking into an electrical course

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