Md. Code Regs. 20.50.06.03 - Test Procedures and Accuracies

A. Procedure. The following procedures shall apply to the testing and adjusting of meters and associated devices:

(1) General. The test of any unit of metering equipment shall consist of a comparison of its accuracy with the accuracy of a standard.

(2) Adjusted to Zero. All meters and associated devices, when tested, shall be adjusted as closely as practicable to the condition of zero error.

(3) Use of Tolerances. All tolerances are to be interpreted as maximum permissible variations from the condition of zero error. In making adjustments, no advantage of the prescribed tolerance limits shall be taken.

(4) Creep. Meters may not creep, that is, there shall be no continuous rotation of the moving element of a meter at a speed in excess of one revolution in 5 minutes when the meter load wires have been removed and voltage is applied to the potential elements of the meter.

B. Watt-Hour Meters. Watt-hour meters shall be tested at the loads and adjusted to the tolerances prescribed below:

(1) Shop Tests.

Test Load	PowerFactor	Adjustedto within
approximately 100% of test current	1.0	1%
approximately 10% of test current	1.0	1%
approximately 100% of test current	.5	2%

(2) Field Tests.

Test Load	PowerFactor	Adjustedto within
approximately 100% of test current	1.0	1%
approximately 10% of test current	1.0	1%

C. Block Interval Demand Meters. Block interval demand meters shall be tested and adjusted as prescribed below:

(1) Test of Indicating Type. Demand meters shall be tested at a load point not less than 50 percent of full scale. However, they may be tested at a lower scale point if conditions warrant. Tests shall be continuous for at least one demand interval, or subinterval in the case of programmable demand register-equipped meters, and shall be started simultaneously with the demand interval of the demand meter.

(2) Test of Pulse-Operated Type. Demand meters which are actuated by pulses shall be tested by transmitting enough pulses to cause the meter to register at a load point not less than 50 percent of full scale. If a pulse actuated demand meter is equipped with a device which records the number of pulses received by the meter, and if there is frequent and accurate comparison of the record with the number of kilowatt hours registered on the associated watt-hour meter, then it is not necessary to make a periodic field test of the demand meter.

(3) Check of Pulse Devices. Pulse devices associated with demand meters shall be checked for proper operation.

(4) Accuracy. The demand meter shall have an accuracy of within 1 percent of full scale.

(5) Time Interval Accuracy. The total time interval, including reset time, shall be accurate within 0.5 percent, except that when a timing element also serves to keep a record of the time of day at which the demand occurs, it shall be adjusted if it is found to be in error by more than +/- 2 minutes per day.

(6) Adjusted to Zero. Demand meters shall be adjusted to indicate zero under no-load conditions, and shall be checked to ascertain that the meter resets to zero.

D. Lagged-Demand Meters. Lagged-demand meters shall be tested and adjusted as prescribed below:

(1) Test Points. Lagged-demand meters shall be tested initially at 50 and 90 percent of full scale. Subsequent tests shall be at not less than 50 percent of full scale.

(2) Accuracy. The lagged-demand meter shall have an accuracy within 2 percent of full scale.

(3) Time Interval Accuracy. The interval rating of lagged-demand meters shall be checked before installation, and the time required for the demand meter to reach 90 percent of final indication, with a constant load suddenly applied, may not vary from the rated demand interval by more than +/- 2 percent.

(4) Adjusted to Zero. Lagged-demand meters shall be adjusted to indicate zero under no-load conditions.

E. Instrument Transformers. The following procedures and requirements shall apply to instrument transformers used for billing purposes:

(1) Standard for Testing. Unless otherwise specified by the Commission, all current and potential transformers shall be tested in accordance with the procedures prescribed in American Standard Requirements, Terminology and Test Code for Instrument Transformers, ANSI C57.13.

(2) Test Facilities. Any utility unable to perform the above test due to a lack of proper equipment may have its instrument transformers tested by another utility or approved meter shop whose testing equipment conforms to the requirements of the Commission.

(3) Test. In lieu of utility testing of instrument transformers, the Commission will accept the certificate of test as furnished by the manufacturer.

(4) Accuracy. Current or potential transformers may not be installed if their accuracy does not fall within the 0.6 accuracy class as defined in ANSI C57.13.

F. Meters For Measurement of Purchased Electricity. Utilities purchasing electricity from non-utilities or from utilities outside the State shall see that the instruments and meters which are necessary to furnish complete and accurate information as to the energy purchased are installed and tested in accordance with the requirements of the Commission.

Notes

Md. Code Regs. 20.50.06.03