The switch didn't trip, the meter light didn't light up, and there was no electricity. What happened?

When the voltage coil of the instrument passes the rated voltage and the rated current is applied to the current coil, the voltage coil and the current coil will produce voltage working flux and current working flux at different positions and phases. When the power factor of the meter is 1, the starting current of the meter is about 0.5~ 1% of the rated current. Therefore, a 10A meter only starts to rotate when the current of 0.05 ~ 0. 10A passes, and its power is equivalent to 12~24 watts on a 220V line. Although ammeter is a precise instrument, there is inevitably mechanical resistance when it rotates. At the beginning of rotation, the precision of the instrument is not high because there is little difference between dynamic torque and mechanical resistance.