The 1 and 3 ports of the circuit diagram are L and N, which are the L live line and N zero line of the 220V input of the power grid respectively. Ports 2 and 4 are L and N live wires and N neutral wires output to household electricity. Ports 5 and 6 are small holes. This is the pulse output of the electric energy meter+-. These two ports are used to connect the watt-hour meter calibration instrument and test the watt-hour meter and its error. The user cannot use them.

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Watt-hour meter: an instrument specially used to measure the accumulated value of electric energy in a certain period, called watt-hour meter, commonly known as watt-hour meter and fire meter. According to usage: active watt-hour meter, reactive watt-hour meter, maximum demand watt-hour meter, standard watt-hour meter, multi-rate time-sharing watt-hour meter, prepaid watt-hour meter (coin-operated, magnetic card type, electric card type), loss watt-hour meter, multifunctional watt-hour meter and intelligent watt-hour meter.

According to the working principle: inductive (mechanical), electrostatic (electronic), mechatronics (hybrid)

According to the nature of power supply: AC meter and DC meter.

According to the structure: integrated, according to the access phase line: single-phase, three-phase three-wire, three-phase four-wire watt-hour meter.

According to the accuracy grade, the installation and wiring modes of ordinary installed electric energy meters (0.2S, 0.5S, 0.2.0.5. 1.0, 2.0) and portable precision electric energy meters (0.0 1, 0.05, 0.2) are direct connection and indirect connection.