Measurement of Maximum Demand

``Maximum demand'' has become an increasingly important item in rates for the sale of electric service since the appearance of Doctor John Hopkinson's notable paper, ``Cost of Electricity Supply,'' in the year 1892-nearly 50 years ago. The writer estimates that the demand-measuring equipment which is now being used by the public utilities of the United States has a value of the order of $100,000,-000. This is an index of its present importance. The object of the present paper is to describe in detail the thermal-storage method of measuring the maximum demand of a user of electric service. A comparison is made between this method, which at each instant of time indicates the logarithmic average load over some nominal time interval, and the commonly used ``block-interval'' method, which indicates the arithmetic average load over the same time interval. Also, the effect of using a modified design of thermal-demand meters is discussed. The writer has contributed a number of previous papers dealing with this same general subject, reference to which will be found at end of paper.