晟(sheng)邦(bang)三(san)(san)相(xiang)(xiang)(xiang)(xiang)電動機(ji)沒(mei)有(you)(you)零(ling)線(xian)，因(yin)為在任意時刻三(san)(san)相(xiang)(xiang)(xiang)(xiang)電的(de)向量之(zhi)和為零(ling)。即使(shi)接了零(ling)線(xian)也沒(mei)有(you)(you)電流存在，所(suo)以(yi)三(san)(san)相(xiang)(xiang)(xiang)(xiang)電動機(ji)沒(mei)有(you)(you)零(ling)線(xian)。三(san)(san)相(xiang)(xiang)(xiang)(xiang)電機(ji)之(zhi)所(suo)以(yi)沒(mei)有(you)(you)零(ling)線(xian)是因(yin)為零(ling)線(xian)與(yu)相(xiang)(xiang)(xiang)(xiang)線(xian)間(jian)的(de)電壓(ya)是220V，而三(san)(san)相(xiang)(xiang)(xiang)(xiang)電機(ji)所(suo)需電壓(ya)是380V，所(suo)以(yi)三(san)(san)相(xiang)(xiang)(xiang)(xiang)電機(ji)要(yao)接三(san)(san)相(xiang)(xiang)(xiang)(xiang)電源線(xian)，而沒(mei)有(you)(you)零(ling)線(xian)。

外(wai)殼接(jie)地(di)(di)(di)(di)(di)的作用是防(fang)止某些相絕緣破損使(shi)外(wai)殼帶電(dian)(dian)(dian)使(shi)人發(fa)生觸電(dian)(dian)(dian)事故。但是變(bian)(bian)頻(pin)(pin)器(qi)的接(jie)地(di)(di)(di)(di)(di)線不要和電(dian)(dian)(dian)動(dong)(dong)機(ji)地(di)(di)(di)(di)(di)線用同(tong)(tong)一個(ge)，因為(wei)在有(you)些潮氣比較重的工廠(chang)環境接(jie)地(di)(di)(di)(di)(di)線有(you)可能時(shi)間(jian)長老化斷裂。以前有(you)個(ge)案(an)例就是一個(ge)工廠(chang)同(tong)(tong)時(shi)燒毀好(hao)幾(ji)臺(tai)(tai)變(bian)(bian)頻(pin)(pin)器(qi)，出現(xian)變(bian)(bian)頻(pin)(pin)器(qi)主板端子有(you)強電(dian)(dian)(dian)打火的現(xian)象(xiang)，燒毀主板。經過(guo)調查發(fa)現(xian)由于有(you)一臺(tai)(tai)電(dian)(dian)(dian)動(dong)(dong)機(ji)漏電(dian)(dian)(dian)，恰好(hao)工廠(chang)地(di)(di)(di)(di)(di)線生銹(xiu)斷開(kai)。強電(dian)(dian)(dian)經過(guo)變(bian)(bian)頻(pin)(pin)器(qi)地(di)(di)(di)(di)(di)線反串(chuan)如變(bian)(bian)頻(pin)(pin)器(qi)主板。所以變(bian)(bian)頻(pin)(pin)器(qi)有(you)單獨(du)接(jie)地(di)(di)(di)(di)(di)點(dian)，不要和電(dian)(dian)(dian)動(dong)(dong)機(ji)公用接(jie)地(di)(di)(di)(di)(di)線。在系統(tong)中，電(dian)(dian)(dian)動(dong)(dong)機(ji)等電(dian)(dian)(dian)氣設備的金屬外(wai)殼，就應(ying)該接(jie)地(di)(di)(di)(di)(di)線，即PE線,一個(ge)供電(dian)(dian)(dian)系統(tong)不能又接(jie)地(di)(di)(di)(di)(di)，又接(jie)零線！