三相電加熱管

        380伏(fu)(fu)三(san)相(xiang)(xiang)(xiang)四線(xian)(xian)電路中(zhong)，任意兩根火線(xian)(xian)之間的(de)電壓都是380伏(fu)(fu)，任意一根火線(xian)(xian)與(yu)零線(xian)(xian)之間都可以組成(cheng)220伏(fu)(fu)。這個系統可以形成(cheng)三(san)種(zhong)(zhong)電源：即(ji)單相(xiang)(xiang)(xiang)220伏(fu)(fu)電源，單相(xiang)(xiang)(xiang)380伏(fu)(fu)電源，三(san)相(xiang)(xiang)(xiang)380伏(fu)(fu)電源，第 I 種(zhong)(zhong)家(jia)用(yong)(yong)(yong)比(bi)較多，第三(san)種(zhong)(zhong)工廠里電機類(lei)用(yong)(yong)(yong)得多，第二種(zhong)(zhong)用(yong)(yong)(yong)得少，只有交流電焊機經(jing)常用(yong)(yong)(yong)到單相(xiang)(xiang)(xiang)380伏(fu)(fu)電源。