三相電加熱管

        380伏(fu)(fu)(fu)三(san)相(xiang)(xiang)四線(xian)(xian)電(dian)(dian)路中，任意兩根火線(xian)(xian)之間的電(dian)(dian)壓(ya)都是380伏(fu)(fu)(fu)，任意一根火線(xian)(xian)與(yu)零(ling)線(xian)(xian)之間都可以組成220伏(fu)(fu)(fu)。這個(ge)系統可以形成三(san)種(zhong)電(dian)(dian)源：即單(dan)相(xiang)(xiang)220伏(fu)(fu)(fu)電(dian)(dian)源，單(dan)相(xiang)(xiang)380伏(fu)(fu)(fu)電(dian)(dian)源，三(san)相(xiang)(xiang)380伏(fu)(fu)(fu)電(dian)(dian)源，第 I 種(zhong)家用比較(jiao)多(duo)，第三(san)種(zhong)工廠里電(dian)(dian)機類用得多(duo)，第二種(zhong)用得少，只有交流電(dian)(dian)焊機經常(chang)用到單(dan)相(xiang)(xiang)380伏(fu)(fu)(fu)電(dian)(dian)源。