Section 502: Meter Accuracy Requirements

I. Objective:

To install and operate accurate meters which properly record the usage of electricity.

II. Policy Content:

To establish an acceptable accuracy limit for installed electric meters.

III. Provisions:

1. No meter shall be placed in service, or allowed to remain in service, which has an
   incorrect register multiplier, watt-hour constant, gear ratio, or dial train; or which is
   mechanically or electrically defective, incorrectly connected, installed, or applied; or
   which registers outside the limits specified in B below.
2. The performance of a watt-hour meter is considered to be acceptable when the
   average percentage registration is not more than one hundred-two percent (102%),
   nor less than ninety-eight percent (98%), calculated in accordance with one of the
   methods described below:
   1. Method 1. Weighted average percentage registration is the weighted average of the percentage registration at light load (LL) and at heavy load (HL) registration a weight of four (4). By this method: Weighted Average Percentage Registration = LL+4 HL
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   2. Method 2. Average percentage registration is the average of the percentage registration at light load (LL) and at heavy load (HL). By this method: Average Percentage Registration = LL+HL
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3. When the test of a watt-hour meter indicates that the error in registration exceed one percent (1%) at either light load or heavy load at unity power factor, or exceeds two percent (2%) at heavy load at approximately 0.5 power factor lag, the percentage registration of the meter shall be adjusted to within these limits of error, as closely as practicable to the condition of zero error. Where instrument transformers are used in conjunction with the meter, these limits apply to the meter equipment as a whole. All meters which are tested shall be left without creep.
4. No watt-hour meter which creeps shall be placed in service or allowed to remain in service. A meter creeps if, with load wires removed and with test voltage applied to the voltage circuits, the rotor or disk simulator moves continuously. For practical recognition of creep in a meter in service, it is considered to creep when, with all load wires disconnected, the rotor or disk simulator makes one (1) revolution in ten (10) minutes or less.
5. The performance of a demand meter or register shall be acceptable when the error in registration does not exceed four percent (4%) in terms of full scale value when tested at any point between twenty-five percent (25%) and one hundred percent (100%) of full scale value.
6. When a demand meter or register indicates that the error in registration exceeds ± four percent (4%) in terms of full scale value, the demand meter or register shall be adjusted to within ± two percent (2%) full scale value. The timing element when used to keep a record of time of day at which the demand occurs, shall be adjusted to condition of as near zero error as practicable when it is found to be in error by more than ± 0.25 percent.

IV. Responsibility

It will be the responsibility of the Manager of Transmission and Distribution Services, Field Services Unit Manager, and Director of Technical Services to properly administer these provisions.

Approved by the Board of Trustees

• Effective Date: January 1, 1994
• Revision Date: July 27, 2009
• 2nd Revision Date: January 23, 2020