In the Three phase and Four wire circuit system, the neutral wire is very important.

在三相四线制供电系统中，中性线是非常重要的。

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In other words, the circuit may be physical two - wire (or even physical one - wire) and logical four - wire, performing as a four - wire circuit but employing fewer than four wires.

换句话说，电路可以是物理双线(甚至是物理单线)、逻辑四线，它使用较少的线实现四线电路。

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In fact, a four - wire circuit can be established without the use of any wires at all, as in the case with a circuit established over microwave, satellite, or infrared transmission systems.

事实上，可以不使用任何线来建立四线电路，例如通过微波、卫星或红外传输系统。

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