Method to check the accuracy class of household electricity meters

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The accuracy class refers to the category or grade of a measuring instrument that meets certain metrological requirements, ensuring that the error remains within specified limits. It is also an important indicator of the quality of the electricity meter. In our country, electricity meters are classified into seven grades: 0.1, 0.2, 0.5, 1.0, 1.5, 2.5, and 5.0. The lower the grade value, the higher the accuracy of the meter. The rating of the commonly used meters is indicated on their dials. A symbol of ① or ② is marked after each value to indicate the Class 1 and Class 2 accuracy levels of the meter. Grade 0.5 means that under standard voltage and current conditions, the error for every 100 units of electricity measured is within plus or minus 0.5% ； A class 1 meter means that, within its measurement range, its error does not exceed ±1; for example, 1200 imp/kwh① and 6400 imp/kwh① indicate that the accuracy class for active power is 1, with the error of smart meters not exceeding ±1% ； A class 2 meter means that, within its measurement range, its error does not exceed ±2%. For example, the labels 6400imp/kwh① and 6400imp/kvarh② indicate that the meter’s active power accuracy rating is class 1, while its reactive power accuracy rating is class 2; the error for active power does not exceed ±1%, and the error for reactive power shall not exceed ±2%. The comprehensive measurement accuracy of Class 1 instruments is higher than that of Class 2 instruments. But some meter accuracy grades have an “S” while others don’t; what’s the difference? “S” indicates a wide measurement range, allowing for an accuracy level of 0.5 when the current exceeds 1% of the rated current. Whether an S is included mainly indicates whether error correction for low-current points is performed when calibrating the meter. In addition to verifying normal current points, those marked with “S” require that the meter meet its accuracy class specifications even when the load current is between 1%In and Imax ； The absence of an “S” indicates that when the load current requirement is between 5%In and Imax, no error tolerance is required. Regarding the accuracy requirement for smart meters, generally, the accuracy class of active energy meters used in residential households should be no less than 2.0 class, while those used by large power consumers with a monthly average energy consumption of 1 million kW/h or more should have an accuracy class of no less than 0.5 class.