三相電加熱管

        380伏三(san)(san)相四線(xian)電(dian)(dian)路(lu)中，任意兩(liang)根(gen)火線(xian)之(zhi)間(jian)的電(dian)(dian)壓都是(shi)380伏，任意一根(gen)火線(xian)與零線(xian)之(zhi)間(jian)都可(ke)以(yi)組成(cheng)220伏。這(zhe)個系統可(ke)以(yi)形(xing)成(cheng)三(san)(san)種電(dian)(dian)源：即單相220伏電(dian)(dian)源，單相380伏電(dian)(dian)源，三(san)(san)相380伏電(dian)(dian)源，第 I 種家用(yong)比較多，第三(san)(san)種工(gong)廠(chang)里電(dian)(dian)機類用(yong)得多，第二種用(yong)得少，只有交(jiao)流電(dian)(dian)焊機經常用(yong)到單相380伏電(dian)(dian)源。