Define coincidence factor

Coincidence factor is the ratio of the maximum demand of a group of consumers taken together to the sum of the individual maximum demands of those consumers:

$$\text{Coincidence factor} = \frac{\text{Maximum demand of the group}}{\sum \text{Individual maximum demands}} = \frac{1}{\text{Diversity factor}} \le 1$$

It is less than 1 because consumers do not all reach their own peaks at the same time. For example, if 50 houses each have a peak of 2 kW but the group peak is 60 kW, the coincidence factor is $60/100 = 0.6$.

Significance in distribution design:

• The peak load on a distribution transformer, LT feeder or service main is found as (number of consumers) × (individual peak) × (coincidence factor). Without it, equipment would be badly oversized.
• It decreases as the number of consumers increases, so a transformer serving many consumers needs less capacity per consumer than a service drop serving one.
• It lets the designer choose smaller, cheaper transformers and conductors while still meeting the actual peak, and gives realistic voltage drop and loss calculations.
• Wrong (too high) values give idle capacity and high no-load losses; too low values cause overloading.