三相電加熱管

        380伏(fu)(fu)三(san)相四線電(dian)(dian)(dian)路中，任意(yi)兩根火線之間(jian)(jian)的電(dian)(dian)(dian)壓都是(shi)380伏(fu)(fu)，任意(yi)一(yi)根火線與零線之間(jian)(jian)都可以組成(cheng)220伏(fu)(fu)。這個系(xi)統可以形成(cheng)三(san)種(zhong)電(dian)(dian)(dian)源(yuan)：即單相220伏(fu)(fu)電(dian)(dian)(dian)源(yuan)，單相380伏(fu)(fu)電(dian)(dian)(dian)源(yuan)，三(san)相380伏(fu)(fu)電(dian)(dian)(dian)源(yuan)，第 I 種(zhong)家用(yong)比較多(duo)，第三(san)種(zhong)工(gong)廠里(li)電(dian)(dian)(dian)機類用(yong)得多(duo)，第二種(zhong)用(yong)得少，只有(you)交流電(dian)(dian)(dian)焊(han)機經常用(yong)到單相380伏(fu)(fu)電(dian)(dian)(dian)源(yuan)。