To check that the light cable is normal, use a multimeter as follows
Most people first set the multimeter to the voltage AC 250V range and check whether the voltage of the live and neutral wires of the light wire is 220V to determine whether the live and neutral wires are intact. This method works if the live or neutral wire is disconnected. However, if the contact is poor and seems to be broken but not broken, it may cause misjudgment. The reason is that when there is poor contact between the live wire or the neutral wire, the internal resistance of the multimeter's voltage range is large and the current in the circuit is very small. This current is not enough to cause a large voltage drop at the poor contact between the live wire or the neutral wire. Therefore, the measured voltage will still be around 220V. Once the power is applied and the load is applied, the voltage drop at the poor contact point will increase significantly, and the power supply voltage at the power supply terminal of the lamp will be much lower than 220V. It will happen that the lamp does not work or does not work properly. Therefore, when measuring with the voltage method, it must be measured with power and load.
The second method is more reliable, that is, use the resistance method, set the multimeter to the lowest ohm range such as RX1, and calibrate to zero, then cut off the power, and disconnect the switch wire and the live and neutral wires on the lamp (to prevent loop), and then use a multimeter to measure the fire and neutral wires respectively. When they are intact, they are zero. When the wires are in poor contact, there is resistance. The greater the resistance, the more serious the poor contact. The resistance is infinite and the wire is broken.
Use a multimeter to test the light wire. There are two types: one is live measurement, set the meter to the AC voltage range, and set the meter needle to the live wire and neutral wire respectively to measure directly to see if the voltage is 220 volts. If it is close to zero volts, it indicates the circuit. There are breaking points. Use an electric pen to test it. If both strands of the wire are red, it means that the neutral wire has been disconnected. Check the connector carefully to see if it is loose.
The second is, power outage measurement. Turn off the power to the circuit knife and use the resistance setting of a multimeter to measure the continuity of the circuit. However, this method is not suitable because the circuit is too long and the meter needle cannot reach it. It is okay to measure the continuity of the light bulb separately.
Based on the above, it shows that using a multimeter to measure the light circuit can only use the voltage range to measure the voltage to judge, which has great limitations.
Turn the digital multimeter to the AC voltage setting, wrap the black test lead wire around your finger three to five times, use the red test lead to touch the neutral wire and the live wire respectively, and compare. The one with the larger reading is the live wire, and the one with the smaller reading is the live wire. The root is the zero line.
