三相電加熱管

        380伏三(san)相四線(xian)電(dian)(dian)路(lu)中，任意兩(liang)根火(huo)線(xian)之(zhi)間(jian)的電(dian)(dian)壓都是380伏，任意一根火(huo)線(xian)與零線(xian)之(zhi)間(jian)都可(ke)以組成220伏。這個(ge)系統可(ke)以形成三(san)種電(dian)(dian)源：即單(dan)相220伏電(dian)(dian)源，單(dan)相380伏電(dian)(dian)源，三(san)相380伏電(dian)(dian)源，第 I 種家(jia)用(yong)比較多，第三(san)種工(gong)廠(chang)里電(dian)(dian)機(ji)類用(yong)得(de)多，第二種用(yong)得(de)少，只有交流電(dian)(dian)焊機(ji)經常用(yong)到單(dan)相380伏電(dian)(dian)源。