How to judge the voltage tester pen according to the exclusion method
If you choose A or B, the short circuit between the live wire and the neutral wire and the short circuit of the lamp L will cause the current in the circuit to be too large, causing the fuse not to blow.
The fuse in the question is not blown. If C is selected, there is an open circuit somewhere in the AC section, which will make C out of contact with the live wire, and will not make the neon tube of the test pen glow. And there is an open circuit somewhere in the BD section, one is to cause the light bulb to be disconnected and not emit light, and the other is to connect the D point with the live wire through the filament, which can make the neon tube glow.
The above briefly analyzes the method of using a test pen to judge the circuit breakage problem, and I hope it will be helpful to everyone.
