三相電加熱管

        380伏(fu)(fu)三(san)相四線(xian)(xian)電(dian)(dian)(dian)路中，任意兩根火(huo)線(xian)(xian)之間的電(dian)(dian)(dian)壓(ya)都是380伏(fu)(fu)，任意一(yi)根火(huo)線(xian)(xian)與零線(xian)(xian)之間都可以組成220伏(fu)(fu)。這個(ge)系統(tong)可以形成三(san)種(zhong)電(dian)(dian)(dian)源(yuan)：即(ji)單(dan)相220伏(fu)(fu)電(dian)(dian)(dian)源(yuan)，單(dan)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)家用比較多(duo)，第三(san)種(zhong)工廠里(li)電(dian)(dian)(dian)機(ji)類用得多(duo)，第二種(zhong)用得少(shao)，只有交流電(dian)(dian)(dian)焊機(ji)經常用到(dao)單(dan)相380伏(fu)(fu)電(dian)(dian)(dian)源(yuan)。