文章主要阐述了中性线的工况和各种不同接地系统中四极开关的应用及应用中需要注意的问题。

The paper mainly gives the work condition of neutral current, introduces application of four-pole switch in different grounding systems and problems to be noticed.

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注2： PEN导线是指将保护导线和中性导线两种功能结合在一起的保护接地中性线。

NOTE 2 A PEN conductor is a protective earthed neutral conductor combining the functions of both a protective conductor and a neutral conductor.

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