三相電加熱管

        380伏(fu)三(san)相(xiang)四線(xian)電(dian)(dian)(dian)路中，任意兩根(gen)火(huo)線(xian)之間的電(dian)(dian)(dian)壓都(dou)是380伏(fu)，任意一(yi)根(gen)火(huo)線(xian)與零(ling)線(xian)之間都(dou)可(ke)以組成220伏(fu)。這個系(xi)統可(ke)以形成三(san)種(zhong)(zhong)電(dian)(dian)(dian)源：即單相(xiang)220伏(fu)電(dian)(dian)(dian)源，單相(xiang)380伏(fu)電(dian)(dian)(dian)源，三(san)相(xiang)380伏(fu)電(dian)(dian)(dian)源，第 I 種(zhong)(zhong)家用比(bi)較(jiao)多，第三(san)種(zhong)(zhong)工廠里電(dian)(dian)(dian)機(ji)類用得多，第二種(zhong)(zhong)用得少(shao)，只(zhi)有交流電(dian)(dian)(dian)焊(han)機(ji)經(jing)常用到單相(xiang)380伏(fu)電(dian)(dian)(dian)源。