三相電加熱管

        380伏(fu)三(san)相(xiang)(xiang)四線電(dian)(dian)路(lu)中，任意(yi)兩根火線之間(jian)的電(dian)(dian)壓都是380伏(fu)，任意(yi)一根火線與零(ling)線之間(jian)都可以(yi)組成(cheng)220伏(fu)。這個系統可以(yi)形成(cheng)三(san)種(zhong)電(dian)(dian)源(yuan)(yuan)：即單(dan)相(xiang)(xiang)220伏(fu)電(dian)(dian)源(yuan)(yuan)，單(dan)相(xiang)(xiang)380伏(fu)電(dian)(dian)源(yuan)(yuan)，三(san)相(xiang)(xiang)380伏(fu)電(dian)(dian)源(yuan)(yuan)，第 I 種(zhong)家用(yong)(yong)比較多，第三(san)種(zhong)工(gong)廠里電(dian)(dian)機類用(yong)(yong)得多，第二種(zhong)用(yong)(yong)得少(shao)，只有交流電(dian)(dian)焊機經常用(yong)(yong)到單(dan)相(xiang)(xiang)380伏(fu)電(dian)(dian)源(yuan)(yuan)。