How to detect live wire or neutral wire leakage with a multimeter

　　Commonly used multimeters are divided into pointer multimeters and digital multimeters; most pointer multimeters do not have a gear to measure AC current, so there is no way to directly measure leakage current; digital multimeters have an AC current measurement gear, so it is completely possible to measure the leakage value of the power supply line; if you have a digital clamp meter, it is most convenient to measure the leakage current.

　　The leakage range includes line leakage and electrical equipment leakage;

　　① Line leakage refers to the leakage current that forms a loop with the ground due to reduced insulation performance of the line itself when the load in the line is not connected to the power supply.

　　② Electrical equipment leakage refers to the leakage current caused by the insulation resistance between the coil inside the equipment and the ground after the equipment is connected to the power supply.

　　No matter what kind of multimeter you use, the insulation resistance of the measured circuit is not standard (the insulation resistance of the circuit must be measured with a dedicated megohmmeter). Even if you use a multimeter to measure the insulation resistance of the circuit, it is only a reference value, and it is very different from the actual insulation resistance value; because the multimeter itself is a 9V stacked battery, it only applies a 9V DC voltage to the circuit measurement, while the voltage of the AC power supply line is 220V or 380V.

　　If you are using a digital multimeter, you can set the multimeter to the AC current range.

　　(1) It is relatively simple to measure line leakage. The multimeter is connected in series in the line or equipment. When the load is not connected to the power supply, the circuit is directly connected in series between the circuit breaker output and the line connector at the lower end of the power supply circuit breaker output (the line connector needs to be disconnected). Note that ordinary digital multimeters should be set to a larger current range at the beginning. The multimeter I use in the figure above is automatically switched. The current value measured at this time is the leakage current in the line.

　　It is very troublesome to measure the leakage of electrical equipment, because the casing of electrical equipment is basically grounded by mechanical devices. If you use a multimeter to measure leakage, you need to vacate the electrical equipment. When the equipment is powered on, connect one end of the multimeter to the ground and the other end to the electrical equipment. At this time, the current measured by the multimeter is the leakage current.

　　(2) How to use a digital multimeter to measure the live wire in a circuit? First, set the digital multimeter to the AC ~750V position, and use the red or black probe of the multimeter to wrap around your hand 3 to 5 times, and insert the other probe into or contact the metal terminal or socket of the conductor. See the figure below.

　　This is based on the principle that the contact between the conductor and the human body will form distributed capacitance (the more turns of the conductor, the greater the capacitance formed with the human body), and the sensitivity of the digital multimeter itself is higher than that of the pointer multimeter. Therefore, the larger the display value of the digital multimeter is.

　　1 above is a measurement method I often use. I usually wrap it around my hand 4 times. The result is ~57V, which is undoubtedly the live wire. The test lead wrapped around my hand does not move, and then use the black test lead to touch the other ground wires N and PE protective grounding.

　　This is based on the principle that the contact between the conductor and the human body will form distributed capacitance (the more turns of the conductor, the greater the capacitance formed with the human body), and the sensitivity of the digital multimeter itself is higher than that of the pointer multimeter. Therefore, the larger the display value of the digital multimeter is, the greater the value will be.

　　The above 1 is a measurement method I often use. I usually wrap it around my hand 4 times. The result is ~57V, which is undoubtedly the live wire. The test lead wrapped around my hand does not move, and then use the black test lead to touch the other ground wires N and PE protective grounding respectively. See Figure 2 below.

　　At this time, the measurement result of the digital multimeter shows 000, which means that the live wire, neutral wire, and PE protective grounding in the circuit have all been detected.

　　As we all know, capacitors can block direct current and pass alternating current. This method is safe, convenient, and can be used in any situation.