三相電加熱管

        380伏(fu)(fu)三(san)相四線電(dian)(dian)路(lu)中(zhong)，任意兩根火線之(zhi)間的電(dian)(dian)壓都是380伏(fu)(fu)，任意一根火線與零線之(zhi)間都可(ke)以組成(cheng)(cheng)220伏(fu)(fu)。這個系(xi)統(tong)可(ke)以形成(cheng)(cheng)三(san)種(zhong)電(dian)(dian)源(yuan)(yuan)：即單相220伏(fu)(fu)電(dian)(dian)源(yuan)(yuan)，單相380伏(fu)(fu)電(dian)(dian)源(yuan)(yuan)，三(san)相380伏(fu)(fu)電(dian)(dian)源(yuan)(yuan)，第 I 種(zhong)家用(yong)比較多，第三(san)種(zhong)工廠(chang)里電(dian)(dian)機類用(yong)得多，第二種(zhong)用(yong)得少，只有(you)交(jiao)流電(dian)(dian)焊機經常用(yong)到單相380伏(fu)(fu)電(dian)(dian)源(yuan)(yuan)。