三相電加熱管

        380伏(fu)三(san)相(xiang)四線(xian)電(dian)(dian)(dian)(dian)路中，任意(yi)兩(liang)根火線(xian)之(zhi)間的電(dian)(dian)(dian)(dian)壓都是380伏(fu)，任意(yi)一(yi)根火線(xian)與零(ling)線(xian)之(zhi)間都可以(yi)組成(cheng)220伏(fu)。這個系(xi)統可以(yi)形成(cheng)三(san)種(zhong)電(dian)(dian)(dian)(dian)源：即單相(xiang)220伏(fu)電(dian)(dian)(dian)(dian)源，單相(xiang)380伏(fu)電(dian)(dian)(dian)(dian)源，三(san)相(xiang)380伏(fu)電(dian)(dian)(dian)(dian)源，第 I 種(zhong)家用比(bi)較多，第三(san)種(zhong)工廠里電(dian)(dian)(dian)(dian)機類(lei)用得多，第二(er)種(zhong)用得少，只(zhi)有(you)交流(liu)電(dian)(dian)(dian)(dian)焊機經常用到單相(xiang)380伏(fu)電(dian)(dian)(dian)(dian)源。