Network cable Tester, twisted-pair cable 1,2,3,4,5,6,7,8,G cable can be to one by one (the) test, and determine which one can be distinguished (for) the wrong line, short circuit and open circuit. Under a RJ45 copper not quite pressure cannot be tested, otherwise it will make the port permanently damage; please use the original good quality crimping tool and Crystal head not bearing the RJ11 port, are able to test telephone RJ11, otherwise will cause the port pins are permanently damaged.