How to use a multimeter to check whether the lamp line is normal
The first step for most people is to set the multimeter to AC 250V and check if the voltage of the live and neutral wires of the light wire is 220V to determine if they are intact. If the live or neutral wire is disconnected, this method is feasible. But if there is poor contact, it may cause misjudgment. The reason is that when there is poor contact between the live or neutral wire, due to the high internal resistance in the voltage range of the multimeter, the current in the circuit taken is very small, and this current is not enough to generate a large voltage drop at the poor contact of the live or neutral wire. Therefore, the measured voltage will still be around 220V. Once the load is energized, the voltage drop at the poor contact area will significantly increase, and the power supply voltage at the lamp power end will be much lower than 220V. If the lighting fixtures do not work or work abnormally, it is necessary to measure with electricity and load when using voltage method.
The second method is more reliable, which is to use the resistance method. Place the multimeter in the lowest ohm range, such as RX1, and calibrate it to zero. Then turn off the power, disconnect the switch wire and the live and neutral wires on the lamp (anti circuit), and use a multimeter to measure the fire and neutral wires separately. When they are intact, they are zero. When the wire contact is poor, there is a resistance value. The larger the resistance value, the more severe the poor contact phenomenon. The resistance value is infinite, and the wire is disconnected.
Use a multimeter to check the light wire, which can be divided into two types: one is live measurement. Set the meter to the AC voltage range, and directly measure the voltage with the meter pins on the live and neutral wires to see if the voltage is 220 volts. If it is close to zero volts, it indicates that there is a break in the circuit. Use an electric pen to measure. If both wires turn red, it means that the neutral wire is already broken. Carefully check the connector to see if it is loose.
Secondly, power-off measurement. Turn off the circuit breaker and measure the continuity of the circuit using a multimeter in the resistance range. However, this method is not very suitable because the circuit is too long and the needle cannot reach. If measuring the continuity of the light bulb separately, it is still possible.
Based on the above, it can be concluded that using a multimeter to measure the circuit of a lamp can only be judged by measuring the voltage in the voltage range, which has significant limitations.
Set the digital multimeter to AC voltage mode, wrap the black probe wire around your finger three to five times, and use the red probe to touch the neutral and live wires respectively for comparison. The wire with the larger reading is the live wire, and the wire with the smaller reading is the neutral wire.
