.05 Adjustment of Bills.

A. Fast Meters. Whenever a meter is tested and found to have over-registered more than 2 percent, the utility shall recalculate the bills for service of the last customer of record receiving service through the meter and shall make a refund if the amount of the adjustment exceeds $1. The refund shall be for the period that the customer received service through the meter, but for not more than the periods established below:

(1) Known Date of Error. If the date on which the error first developed or occurred can be established, the bills for service shall be recalculated from that time.

(2) Unknown Date of Error. If the time at which the error first developed or occurred cannot be established, it shall be assumed that the over-registration existed for a period of 3 years or a period equal to one-half of the time since the meter was last tested, whichever is less.

B. Slow Meters. Whenever a meter is found to be more than 2 percent slow, the utility may bill the customer one-half of the unbilled error for a period of 12 months, unless the meter has been tested within that 12-month period, in which event the utility may bill the customer one-half the unbilled error for the period since the meter was last tested. If the amount of under-registration is less than $5, the utility may not adjust the bill.

C. Accuracy Calculation. Billing adjustments due to fast or slow meters shall be calculated on the basis that the meter should be 100 percent accurate. For watthour meters, the average accuracy shall be the arithmetic average of the percentage registration at light load and at heavy load, giving the heavy load registration a weight of 4.

D. Overcharge—Undercharge Adjustment. When a customer has been overcharged or undercharged for services because of incorrect application of the rate schedule, incorrect calculation of charges, or other similar reasons, the amount of overcharge or undercharge adjustment shall be determined separately during the period of time the discrepancy occurred, in accordance with the following:

(1) Overcharge Adjustment. The total overcharge for the period the discrepancy occurred shall be refunded or credited to the customer, except for an overcharge resulting from an incorrect reading of the meter when the amount shall automatically be corrected in a subsequent billing based on the correct meter reading.

(2) Undercharge Adjustment.

(a) Unless authorized by the Commission, retroactive billing may not be for undercharging which occurred more than 12 months before the discovery of the error. A utility may seek the Commission's authorization for retroactive billing for undercharges which occurred more than 12 months but not more than 3 years before the discovery of the error if the customer knew, or reasonably should have known, that the bills were in error. The utility's request to the Commission shall be in writing and shall explain the factual basis for the request to the customer with a notice of the customer's right to write to the Commission, within 20 days, if the customer is in opposition to the request.

(b) If the total undercharge is more than 35 percent of the customer's average monthly bill during the preceding 3 months, the customer shall be allowed to enter into an installment plan to pay the total retroactive billing, without interest. In such a plan the monthly payments against the undercharge may not exceed 35 percent of the customer's average monthly bill during the preceding 3 months. However, if the installment plan will not recover within a 12-month period the total undercharge, the monthly payment may be equal to the total undercharge divided by 12 or a number greater than 12.

(c) Unless otherwise authorized by the Commission, the utility may deny service for nonpayment only for that portion of the undercharge applicable to the 4 months immediately before the discovery of the error.

E. If requested by a customer, a utility shall provide means by which any undercharge may be paid in installments over a reasonable period of time, but not less than the same period in which any undercharges were incurred.

F. Theft of Service.

(1) If a meter is found not to register, in whole or in part, due to tampering or interference with the company’s material, equipment, or facilities, the utility may issue an estimated bill.

(2) The company shall retain all information relied on to calculate the estimated bill for not less than 3 years or until the conclusion of a Commission investigation, whichever is longer.