How do you calculate the service factor?

One type of service factor for an electric power supply might be the average power supplied divided by the maximum power that can be supplied.

For a domestic user the supply might allow 15 kVA to be drawn, while the average load throughout the year might be only 0.75 kVA, so in that case the service factor is 0.05 or 5%.

Statistical predictions can be made for groups of consumers, so that a street of 50 houses for example does not require a supply transformer rated at 50 x 15 kVA, it can be supplied by a smaller transformer depending on the usage statistics for that area.

The factor is calculated from the known statistics for each area and this can be done by using the energy bills over a long period like 12 months.