Hi Waross,
The information above is from Jacksonville Electric Authority (JEA), that operate in Florida.
Those data are based in local statistic history of demand for their customer in their region. Even though this is a good generic information, those data are not universal and have to be validated based in local conditions of the load behaviour and supplemented with experience or measuments.
In colder climate, usually the higher demand happens in summer time and coincide with the lowest rating capacity of the equipment, cable and other system components. As an example, see the enclose curve for transformer rating based in 30oC for 24 hr average ambient temperature.
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Saladhawks
The definition of diversity factor could be as you say and as presented above. Please remember that those factors are statistic indicators used for load estimation purpose.
What it is important, is how you use then to calculated the estimated size of transformer, feeder and other equipment.
For instance, the following two cases are equivalent:
a) For diversity Factor, DF1<1
Transf. Size > Est. Individual demand*No Customers* DF
1
b) For DF2 >1
Transf. Size > Est. Individual demand*No Customers / DF
2
Beware that utility may not require to comply with NEC. For work under the jurisdiction of NEC or other codes, the mandate requirement should be accommodated by selecting equipment and conductors that are adequate to supply the code-complying load.