(1)應(yīng)有明顯的斷開點(diǎn); (2)斷開點(diǎn)應(yīng)具有足夠的絕緣; (3)應(yīng)有足夠的短路穩(wěn)定性; (4)動(dòng)作簡(jiǎn)單,結(jié)構(gòu)可靠。