R08-13 PERIODIC TESTS OF METERS
Each watt hour meter shall be tested according to the following schedule, while connected, if practical, in its permanent position in place of service:
(1) Two and three wire commutating type and mercury type meters, up to and including 50 amperes rated capacity of meter element, shall be tested at least once every 18 months.
(2) Two and three wire commutating type and mercury type meters of over 50 amperes rated capacity of meter element shall be tested at least once every 12 months.
(3) Two and three wire single phase induction type meters, up to and including 25 amperes rated capacity of meter element, shall be tested at least once every 96 months.
(4) Two and three wire single phase induction type meters of over 25 amperes rated capacity of meter element shall be tested at least every 96 months.
(5) Self contained polyphase meters, up to and including 50 kW rated capacity, shall be tested at least once every 72 months.
(6) Self contained polyphase meters of over 50 kW rated capacity shall be tested at least once every 72 months.
(7) Polyphase meters, connected through current transformers or current and potential transformers, to circuits up to and including 50 kW rated capacity, shall be tested at least once every 48 months.
(8) Polyphase meters, connected through current transformers or current and potential transformers, to circuits of over 50 kW rated capacity, shall be tested at least once every 48 months.
(9) A statistical sampling program for self contained single phase watt hour meters may be used by any utility in lieu of the periodic testing program specified under subdivisions (3) and (4) above provided the utility files with the Commission a statistical sampling plan which is approved by the Commission and which conforms to the following criteria:
a. The plan submitted shall conform to accepted principles of statistical sampling and should be evaluated by qualified independent mathematical statisticians.
b. The plan shall include an adequate policy for testing meters on request and a consumer protection procedure for high bills due to fast meters to compensate for the fact that an individual meter may not be tested for a period longer than the present eight year schedule.
c. Meters shall be divided into homogeneous groups such as manufacturer's types and, if necessary, into homogeneous groups on the basis of location or other environmental factors which may affect the performance of the meters.
d. A sample shall be taken each year, from each homogeneous group, of a sufficient size to demonstrate with reasonable assurance the condition of the group from which the sample is drawn.
e. It is extremely important that each meter in each group be drawn with known probability, and the sample must be selected at random. (In most probability sampling systems involved in meter registration control, it is expected that every meter in the group will have an equal chance to be drawn; however, the criteria are written to allow a wider choice of probability sampling systems.) In order to accomplish random sampling, it is necessary to use a table of random numbers, or some equivalent mechanical or numerical procedure.
f. The sampling plan shall be designed to provide information on which the utility may base a program to maintain its meters in an acceptable degree of accuracy throughout their service life in accordance with the requirements of the Commission and in keeping with proper standards for good customer relations. The plan shall contain a table of mathematically calculated sample sizes and related values in accordance with g below for determining the characteristics of the homogeneous groups, accompanied by curves for determining the risk of making an incorrect decision which may be detrimental to the customer or to the utility.
g. An acceptable sampling program is one having the property that, when applied to a meter group in which the proportion of meters with registrations greater than 102% is as high as 0.03, then the probability that the group will be judged to be satisfactory (and no corrective action taken) shall be no greater than 0.05. A sample size at least 400 meters for a plan based on the attributes method is recommended. If a variable plan is used, select a minimum sample size so that the variable plan under minimum sample size will have roughly the same operating characteristics curve as the attributes plan for the minimum sample size stated above. If a group of meters does not meet the performance criteria, then an established program of corrective action shall be followed.
h. The corrective action shall consist of an accelerated test and maintenance program to raise the accuracy performance of the group to acceptable standards or it may consist of retirement of the meters in the group from service in an accelerated rate. The accelerated test program should provide for testing at rates which vary in accordance with the calculated percentage of meters in the group outside the acceptable limits of accuracy but not less than 20% of the group tested per year. When any group of meters is so placed on an accelerated test program the meters, selected each year for test, shall be selected on the basis of the longest time since last test. Meters so tested and placed into service shall be sampled as a separate group from the remainder of the original group not tested. When the sample results of the remainder of the original group indicate that the group has come up to acceptable limits the two components of the group may be consolidated for sampling.
i. Reports shall be made to the Commission annually to indicate the number of meters in each homogeneous group in service at the beginning of each year, the number of meters making up the sample for each such group, the test results for each group and any corrective action taken.
(NCUC Docket No. M-100, Sub 5, 7/15/65; NCUC Docket No. E-100, Sub 4, 6/8/66; NCUC Docket No. M-100, Sub 140, 12/03/13.)