三相電加熱管

        380伏(fu)三(san)(san)相(xiang)四(si)線電(dian)(dian)(dian)路中，任(ren)意(yi)兩根火線之間的(de)電(dian)(dian)(dian)壓(ya)都是380伏(fu)，任(ren)意(yi)一根火線與(yu)零線之間都可以(yi)組成(cheng)220伏(fu)。這個(ge)系統可以(yi)形(xing)成(cheng)三(san)(san)種(zhong)電(dian)(dian)(dian)源(yuan)(yuan)：即單相(xiang)220伏(fu)電(dian)(dian)(dian)源(yuan)(yuan)，單相(xiang)380伏(fu)電(dian)(dian)(dian)源(yuan)(yuan)，三(san)(san)相(xiang)380伏(fu)電(dian)(dian)(dian)源(yuan)(yuan)，第 I 種(zhong)家(jia)用比較多(duo)(duo)，第三(san)(san)種(zhong)工(gong)廠里電(dian)(dian)(dian)機類用得多(duo)(duo)，第二種(zhong)用得少(shao)，只有交流(liu)電(dian)(dian)(dian)焊機經(jing)常用到(dao)單相(xiang)380伏(fu)電(dian)(dian)(dian)源(yuan)(yuan)。