1. 1. Method of Determining Average Error of Meters.

   1. A. Field testing the average error of a service watt-hour meter shall be determined as follows: The error at Light Load, here defined as approximately 10% of the rated capacity (Test Amperes) of the meter, shall be determined by taking the average of at least two errors determined from as many separate tests on the same Light Load, which error must agree within one-half percent (1/2 %).

      In the same manner, the error at Full Load, here defined as approximately the rated capacity (Test Amperes) of the meter, shall be determined. The average error of the meter shall then be determined by taking the average error at Light Load plus four times the error at Full Load (Test Amperes) and dividing this sum by five, proper consideration being taken of the sign of the two errors.

   2. B. Meter Shop Testing—When an electronic test board is used, the average error of a watt-hour meter shall be determined as follows: The error at Light Load, here defined as approximately 10% of the rated capacity (Test Amperes) of the meter, shall be determined. The error at Full Load, here defined as approximately the rated capacity of the meter or Test Amperes, shall be determined. The average error of the meter shall then be determined by taking the error at Light Load plus four times the error at Full Load (Test Amperes) and dividing this sum by five, proper consideration being taken of the sign of the two errors.

2. 2. Meter Accuracy.

   1. A. Creeping: No watt-hour meter which registers on “no load” when the applied voltage is less than one hundred and ten (110%) percent of standard service voltage shall be placed in service or allowed to remain in service.

   2. B. Initial Accuracy Requirements—No watt-hour meter shall be in service which is in any way defective to impair its performance, or which has incorrect constants, or which has not been tested individually or under a sample meter testing plan approved by the commission for accuracy of measurement and adjusted, if necessary, to meet these requirements at unity power factor:

      Average error not over 0.5% plus or minus;

      Error at Full Load (Test Amperes) not over 0.5% plus or minus;

      Error at Light Load not over 1.0% plus or minus.

   3. C. Adjustment After Test—Whenever a test made by an electrical utility, contract vendor by or on behalf of the electrical utility or by the ORS on a service watt-hour meter connected in its permanent position in place of service shows that the average error is greater than that specified allowed above, the meter shall be adjusted to bring the average error within the specified initial accuracy limits, or the meter shall be replaced.

3. 3. Test Instruments.

   Each electrical utility shall own and maintain such standard watt-hour meters, such instrument transformers, voltmeters, ammeters and such other instruments necessary in maintaining the accuracy of its standards used in testing the meters serving its customers.

HISTORY: Amended by State Register Volume 32, Issue No. 5, eff May 23, 2008.