Wiring of Three-Phase Electric Meters

For three-phase electric meter, there are three wires and four wires electric meter. In three-phase four-wire system, in the low-voltage distribution network, the transmission line generally adopts the three-phase four-wire system, of which three lines represent A, B, and C three-phase, and the other is the neutral line N or PEN.

In the single-phase transmission line entering the user, there are two lines. One we call the phase line L and the other we call the neutral line N. The neutral line normally passes current to form a current loop in a single-phase line. In a three-phase system, when the three phases are balanced, the neutral line (zero line) has no current, so it is called a three-phase four-wire system. In the 380V low-voltage distribution network, in order to obtain the 220V phase-to-phase voltage from the 380V line-to-line voltage, the N line is set up. On some occasions, it can also be used for zero-sequence current detection, so as to monitor the balance of the three-phase power supply.

First of all, you have to understand what a three-phase four-wire power supply circuit is: Three-phase four-wire system means that there are three live wires (U, V, W) and one neutral wire (N) in the three-phase AC power supply. The voltage between every two live wires is 380V, which is called the line voltage. The voltage between any live wire and the neutral wire is 220V, which is called the phase voltage. Therefore, no matter how much power the 220V bulb is, it should be connected to the phase voltage, that is, one is connected to the neutral wire, and the other is connected to any live wire.

In the three-phase four-wire system, the function of the neutral wire is:

1. When the three-phase load is unbalanced, the neutral line is turned on, and the unbalanced current flows back to the neutral point so that the line voltage and phase voltage of the power supply system are basically balanced.

2. When the insulation of the electrical equipment connected to zero is damaged and the shell is hit, the short-circuit current will form a loop through the zero line. Since the neutral line impedance is small, the short circuit current will be large. It prompts the protection device to act quickly to disconnect the power supply, thus playing a protective role.

3. The neutral line is also the power circuit of single-phase 220V electrical equipment.

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