三相(xiang)(xiang)(xiang)(xiang)五(wu)线(xian)制包括(kuo)三相(xiang)(xiang)(xiang)(xiang)电(dian)的(de)(de)(de)三个(ge)相(xiang)(xiang)(xiang)(xiang)线(xian)（A、B、C线(xian)）、中(zhong)性线(xian)（N线(xian)）以及地线(xian)（PE线(xian)）。中(zhong)心线(xian)（N线(xian)）就(jiu)是零线(xian)。三相(xiang)(xiang)(xiang)(xiang)负(fu)载对称时，三相(xiang)(xiang)(xiang)(xiang)线(xian)路流入中(zhong)性线(xian)的(de)(de)(de)电(dian)流矢量(liang)和为零，但对于单独的(de)(de)(de)一相(xiang)(xiang)(xiang)(xiang)来讲(jiang)，电(dian)流不(bu)为零。三相(xiang)(xiang)(xiang)(xiang)负(fu)载不(bu)对称时，中(zhong)性线(xian)的(de)(de)(de)电(dian)流矢量(liang)和不(bu)为零，会产生对地电(dian)压。

三相五线(xian)(xian)(xian)(xian)(xian)制的特点如下：1、系统正常运行时，专(zhuan)用(yong)(yong)保(bao)护(hu)线(xian)(xian)(xian)(xian)(xian)上(shang)(shang)不有(you)电(dian)流，只是(shi)工(gong)作(zuo)零线(xian)(xian)(xian)(xian)(xian)上(shang)(shang)有(you)不平衡电(dian)流。PE线(xian)(xian)(xian)(xian)(xian)对地没(mei)有(you)电(dian)压，所(suo)以电(dian)气设(she)备金属外壳接零保(bao)护(hu)是(shi)接在专(zhuan)用(yong)(yong)的保(bao)护(hu)线(xian)(xian)(xian)(xian)(xian)PE上(shang)(shang)，安(an)全(quan)可靠(kao)；2、工(gong)作(zuo)零线(xian)(xian)(xian)(xian)(xian)只用(yong)(yong)作(zuo)单相照明负载回路；3、专(zhuan)用(yong)(yong)保(bao)护(hu)线(xian)(xian)(xian)(xian)(xian)PE不许断线(xian)(xian)(xian)(xian)(xian)，也不许进入漏(lou)电(dian)开(kai)关；4、干线(xian)(xian)(xian)(xian)(xian)上(shang)(shang)使用(yong)(yong)漏(lou)电(dian)保(bao)护(hu)器，工(gong)作(zuo)零线(xian)(xian)(xian)(xian)(xian)不得有(you)重复接地，而PE线(xian)(xian)(xian)(xian)(xian)有(you)重复接地，但(dan)是(shi)不经过漏(lou)电(dian)保(bao)护(hu)器，所(suo)以TN-S系统供电(dian)干线(xian)(xian)(xian)(xian)(xian)上(shang)(shang)也可以安(an)装漏(lou)电(dian)保(bao)护(hu)器；5、TN-S方式供电(dian)系统安(an)全(quan)可靠(kao)，适用(yong)(yong)于工(gong)业与(yu)民用(yong)(yong)建筑等低压供电(dian)系统。