Re: Mike Holt Letter to Editor in nec digest
Load diversity is the difference between the sum of the peaks of two or more individual loads and the peak of the combined load. The diversity factor is defined as the ratio of the sum of the individual maximum demands of the various subdivisions of a system (or part of a system) to the maximum demand of the whole system (or the part of the system under consideration). It is equal to or greater than 1; it is 1 if all individual maximum demands occur simultaneously, or are coincident. For most loads it generally varies between 1.0 and 2.0. It should not be confused with Demand Factor which is the ratio of the maximum demand of a system to the total connect load on the system. This factor is always less than 1.
From a design point of view, multiplying the maximum demand on a system by the diversity factor could allow you to accurately predict the load on the main feeder to the system and to size the condutors appropriately. The rub is, of course, that you rarely know this information. As a design engineer I have only been able to use it in special design situations where I could get the information from time of day metering in existing facilities. In designing new facilities the best I usually can do is to use the Demand Factors in the tables in the NEC.
This is pretty lengthy and somewhat convoluted but I hope it helps to answer your question. While diversity factors are very useful to utilities and they have extensive tables based on experience to use in order to apply them, I agree that at our level we don't have much, if any, occasion to use them.
