某厂新建宿舍照明安装验收时,发现一种异常现象:宿舍各层照明均能正常接通和断开电源(每层均装照明分开关,见接线图),但是,三楼A相火线和零线间电压虽然正常,用测电笔验电时,发现零线竟然能使电笔发光,亮度和检测电源火线时相同,而A相电源线却不能使电笔发光。检 An installation of a new factory lighting installation acceptance, found an abnormal phenomenon: the dormitory lights can be turned on and off the normal power supply (each floor is equipped with lighting sub switch, see the wiring diagram), but the third floor of the A phase fire wire and Although the voltage between the neutral lines is normal, when using a pencil to inspect the power, it is found that the zero line can actually make the light pen glow, and the brightness is the same as when the power source is detected. However, the A-phase power line cannot make the light pen emit light. Inspection