How To Choose The Capacity of Household Electricity Meter？(3)
How many amps does a typical household electric meter have?
Selection of the capacity of the electric meter: The capacity of the electric meter should be selected between 20 and 120% of the rated current of the electric meter. Single-phase 220V lighting installations should be calculated at 5 amps per kilowatt, and three-phase 380V power consumption should be calculated at 1.5 amps or 2 amps per kV.
The size of the current of the electric meter: the rated current of the general household electric meter should not be greater than 10 amps. This is because:
When the power factor is 1, the starting current of the meter is about 0.5~1% of the rated current. Therefore, a 10A meter needs to have a current of 0.05~0.1A before it starts to rotate. On a 220V line, its power is equivalent to 12~24 watts. Although an electric meter is a precision instrument, there is still unavoidable mechanical resistance when it is rotated. At the beginning of the rotation, since the motor torque is not much different from the mechanical resistance, in this case, the accuracy of the meter is not high.
A calibrated meter can only guarantee that under the rated voltage, when the current is within the range of 10~100% of the rated current, and the power factor is 0.5~1, its error will not exceed 1~2%. That is to say, a 10A meter can only achieve accurate measurement when the load is 110~2200 watts. At present, the wattage of electricity in general households does not exceed this range. If the nameplate current of the electric meter exceeds 10A, the purpose of the measurement standard will not be met, so it is not suitable for use.
Installation of the electricity meter.
1. The meter should be installed on a wall or switchboard that is not easily affected by vibration, and the distance from the ground should be between 1.7 and 2 meters.
2. The place where the meter is installed should be clean, dry, and free from strong magnetic fields, and should be located in an obvious place for reading and monitoring.
3. The meter should be installed in the box where it is susceptible to mechanical damage, dirt, and touch.
4. The meter should be installed vertically, and the allowable deviation should not exceed 2°.
Power-on check: Power on to check whether the meter is working properly. If there are abnormal phenomena such as non-rotation, reversal and excessive error, the reasons should be analyzed and eliminated. Most of these faults are caused by wiring errors. The reason for the reversal may be that the polarity of the voltage and current coils are reversed, the polarity of the current and voltage transformers are reversed, or the load may be abnormal. For example, in the load of a three-phase active watt-hour meter, when a motor with a larger capacity runs overspeed, the motor becomes a generator operation, and the active watt-hour meter will reverse.
Calculate and check the operation of the electric meter: The electric meter should be calculated and checked after it has been put into use for a period of time. Sometimes, although the wiring is wrong, it is difficult to observe the operating state of the watt-hour meter alone. Therefore, it is necessary to calculate according to the power, power factor and working time of the load, and compare the calculation result with the reading of the watt-hour meter to confirm the reliable operation of the watt-hour meter.
