According to the national standard GB/T15283-94 and the international standard IEC521-1988, the electric energy meter is marked with two current values, such as 10(20)A. The 10A marked here is the basic current (basic current), symbol, is the current value that determines the relevant characteristics of the instrument, also known as the calibration current. The (20)A in parentheses is the rated maximum current, symbol, and is the maximum current value that the instrument can meet the accuracy specified in the standard. The current through the energy meter can be as high as 2~8 times the basic current, and it is not up to 2 times that only the basic current value is marked on the meter. That is to say, if a user's energy meter is marked with only one current value, such as 5A, this is only the basic current value, not the maximum current allowed to pass. For this kind of energy meter, it can generally be overloaded to 120% without problems, and can meet the accurate measurement of the energy meter. On the other hand, due to the large resistance of the rotation mechanism, the starting current of the induction energy meter cannot be less than 0.5% of the basic current (the accuracy level of the electric energy meter), which shows that the energy meter may not start when the light load is below 0.5% of the basic current.
In China, the voltage of the power supply line of the family house is 220V, the frequency is 50Hz, and the rated voltage and applicable frequency of the selected energy meter should be consistent with the voltage and frequency of this line, and it should also be 220V, 50Hz.
When choosing an energy meter, the current value selection is the most important and complex. One is the starting current, which is the minimum current that can make the turntable rotate continuously; The second is the multiple of the maximum rated current relative to the basic current. Also, there are differences in performance between legacy and modern tables. The old electric energy meter still in use in the old house has a relatively large starting current, generally (5%~10%); The maximum rated current is small, generally ≤2, only one current value is marked on the dial surface, and it is generally called the rated current. Therefore, in the old electrician's manual, it is pointed out that the current of the load circuit should be greater than 10% of the rated current, less than 120% or less than 125% when used.
According to the national standard GB/T15283-94 and the international standard IEC521-1988 produced electric energy meters, the starting current of the electric energy meters used in new residential buildings is small, which is 0.5% for the stage meter; The maximum rated current is large, generally the maximum rated current is (2~4), and some can reach (6~8). The dial of the new energy meter is marked with two current values, such as 5 (20A), when selecting this energy meter, on the one hand, pay attention to the minimum load current can not be lower than the starting current, that is, 0.5%×≥5A=0.025A; On the other hand, the ammeter value for long-term use cannot be higher than the maximum rated current value of 20A. When choosing an electric energy meter, it should be taken into account that more and more electrical appliances are entering the home, and there should be a margin, but also reasonable and moderate, because the larger the multiple, the higher the price of the meter.
The current value 10 before the parenthesis is called the calibration current, which is used as the calculation of the load base current value, and the current 20 in parentheses is called the rated maximum current, which can make the energy meter work normally for a long time, and the error and temperature rise fully meet the maximum current value specified requirements. According to the requirements of the regulations, the calibration current of the direct access type electric energy meter should be determined according to the rated maximum current and overload multiple, wherein the rated maximum current should be determined according to the approved load capacity reported by the customer; Overload multiple, for the actual load current of the energy meter in normal operation reaches more than 30% of the maximum rated current, it is advisable to take 2 times the meter; If the actual load current is less than 30%, the meter should be taken 4 times.
