電線的電阻與線徑是成反比的，因此線徑越細，電阻越大。在流過相同的電流時，電阻越大，越容易發熱。大家在生活中也有感受 細(xi)電(dian)(dian)(dian)線(xian)(xian)容(rong)易(yi)發(fa)熱(re)，這是把電(dian)(dian)(dian)能轉化(hua)成熱(re)能浪費了。另外在電(dian)(dian)(dian)路中還可以把電(dian)(dian)(dian)線(xian)(xian)看成是與用電(dian)(dian)(dian)設(she)備串聯(lian)，在串聯(lian)電(dian)(dian)(dian)路中，電(dian)(dian)(dian)阻越大，分配的電(dian)(dian)(dian)壓越多，那么用電(dian)(dian)(dian)設(she)備上(shang)分的電(dian)(dian)(dian)壓將(jiang)減少。因此可以認定在相同條件(jian)下(xia)，電(dian)(dian)(dian)線(xian)(xian)細(xi)越耗電(dian)(dian)(dian)。

電線(xian)(xian)粗細（電線(xian)(xian)截面積）對應的(de)是負載能力，也就是允許的(de)正常工作電流。純理(li)論上線(xian)(xian)徑越粗線(xian)(xian)路(lu)損耗(hao)越小，線(xian)(xian)徑越小線(xian)(xian)路(lu)損耗(hao)越大，這是不會錯的(de)。但不能為了10年(nian)省一(yi)度(du)電而(er)盲(mang)目增加(jia)線(xian)徑。這(zhe)即(ji)不經濟也沒必要。選(xuan)擇時應以電線(xian)允許的(de)標稱電流(liu)能(neng)匹配線(xian)路(lu)的(de)較大工作電流(liu)為準。有人提(ti)到發(fa)生短路(lu)性故(gu)障(zhang)工作電流(liu)急劇增大，這(zhe)個不是(shi)靠加(jia)粗線(xian)徑能(neng)解決的(de)，而(er)要靠配電箱(xiang)中(zhong)選(xuan)擇合適的(de)斷路(lu)器來保(bao)證用電可靠的(de)。

電(dian)(dian)(dian)線(xian)細(xi)會多(duo)耗(hao)(hao)電(dian)(dian)(dian)，原因有兩個，一是電(dian)(dian)(dian)線(xian)細(xi)時(shi)，電(dian)(dian)(dian)阻大(da)，同樣電(dian)(dian)(dian)流情(qing)況下的(de)發熱(re)量(liang)大(da)，多(duo)耗(hao)(hao)電(dian)(dian)(dian)。二，電(dian)(dian)(dian)阻大(da)時(shi)，壓(ya)降(jiang)大(da)，負載的(de)電(dian)(dian)(dian)壓(ya)低，對于很多(duo)負載，比如(ru)說電(dian)(dian)(dian)機，電(dian)(dian)(dian)壓(ya)低會導致效(xiao)率低下，電(dian)(dian)(dian)流反而增加，耗(hao)(hao)電(dian)(dian)(dian)量(liang)會大(da)幅增加的(de)。

電線越(yue)小電阻越(yue)大(da),相(xiang)對來說會(hui)多耗電(dian)些,但多損耗部(bu)份幾乎可以忽略不(bu)計。并(bing)非電(dian)線(xian)越粗就越省(sheng)電(dian)。但是(shi)這要看具體情(qing)況(kuang)，當電(dian)路接(jie)通(tong)后，發(fa)現電(dian)線(xian)發(fa)熱，電(dian)能消耗在導線(xian)上了(le)一部(bu)分，當然就是(shi)電(dian)線(xian)細費電(dian)了(le)。注意遇到這種(zhong)情(qing)況(kuang)應該及(ji)時更換比較(jiao)粗的電(dian)線(xian)防止事故發(fa)生(sheng)。