Sec. 166.1. Classification of utilities

(a) For the purpose of applying systems of accounts prescribed by the commission, utilities are divided into four classes as follows:

Class A. Utilities having annual electric operating revenues of $2,500,000 or more.

Class B. Utilities having annual electric operating revenues of $1,000,000 or more but less than $2,500,000.

Class C. Utilities having annual electric operating revenues of $150,000 or more but less than $1,000,000.

Class D. Utilities having annual electric operating revenues of $25,000 or more but less than $150,000.

(b) This system of accounts applies to Class A and Class B utilities. The system of accounts applicable to Class C and Class D utilities is issued separately.

(c) The class to which any utility belongs shall originally be determined by the average of its annual electric operating revenues for the last three consecutive years. Subsequent changes in classification shall be made when the annual electric operating revenues for each of the three immediately preceding years shall exceed the upper limit, or be less than the lower limit, of the annual electric operating revenues of the classification previously applicable to the utility.