To check for circuit leakage, a megohmmeter (megger) should be used, as the voltage of the multimeter is lower (9V) and the voltage of the megohmmeter is higher (500V). Because the working voltage of the circuit is 220V, it is difficult to diagnose circuits with insignificant leakage. To use a digital meter to check for circuit leakage, you first need to cut off the power supply, discharge the circuit, and measure it with a resistance level of 2M. The normal display is 1 (infinite).

Measuring whether the circuit is in a connected state can be measured using a multimeter's ohm range. When measuring, it is necessary to select a range where the meter pointer is close to 0 ohms of deflection. If the circuit is in a circuit, one end (A end) of the circuit should be connected to a multimeter (red lead) at 100 ohms, and the black lead should be connected to the other end (B end) of the circuit to be measured. If the measured result is zero, it indicates that the circuit is connected, also known as a path. Only a path can current flow through the circuit; If the multimeter ohmmeter pointer at the A to B end of the circuit is not close to zero ohms, the circuit is already in an open circuit state, and disconnection is called an open circuit or an open circuit.