380伏(fu)三相四(si)線(xian)電路中,任(ren)(ren)意(yi)(yi)兩(liang)根(gen)火線(xian)之間的電壓都(dou)是(shi)380伏(fu),任(ren)(ren)意(yi)(yi)一根(gen)火線(xian)與零線(xian)之間都(dou)可以組(zu)成220伏(fu)。這個系(xi)統可以形成三種(zhong)電源(yuan)(yuan)(yuan):即單(dan)相220伏(fu)電源(yuan)(yuan)(yuan),單(dan)相380伏(fu)電源(yuan)(yuan)(yuan),三相380伏(fu)電源(yuan)(yuan)(yuan),第 I 種(zhong)家(jia)用(yong)(yong)比較多(duo),第三種(zhong)工廠(chang)里電機類用(yong)(yong)得(de)多(duo),第二種(zhong)用(yong)(yong)得(de)少,只有交流電焊機經常用(yong)(yong)到單(dan)相380伏(fu)電源(yuan)(yuan)(yuan)。