If the measured value is above {{0}}.5 megohm, or shows infinity, then there is no problem with the insulation of the line, that is, there is no leakage in the line; if the measured value is below 0.5 megohm, then the line insulation is unqualified, and there is leakage . Find all the joints and junction boxes in the line after the open circuit, whether the insulation of the joints is not done well, and then check with a multimeter at each joint and junction box by resistance measurement. The reason is that the short-circuit momentarily generates a large current and the circuit breaker automatically trips, and the line will not burn out much. Generally, the location of the short-circuit can be determined by resistance measurement at the joint or junction box. Then there is the inspection of line leakage by resistance method. Use a multimeter to connect one test lead to live wire or neutral line, and one test lead to ground. Normally, the resistance is infinite. If there is resistance or the resistance is very small, then the measured line exists. grounding phenomenon. The premise is to ensure that there is no short circuit in the line, otherwise it cannot be judged. In the current household power distribution, circuit breakers and leakage circuit breakers are generally installed for protection. Under such power distribution protection, there is no need to use a multimeter to detect whether the line is short circuited or grounded (accurate detection) except for the short-circuit point or the accurate grounding point of the test). Because if the line is short-circuited, the short-circuit protection function of the circuit breaker has already tripped and opened, and if the line is grounded, the leakage protection function of the leakage circuit breaker (opening with a prominent leakage action reset button) has already operated Tripped off.
But I still answer the question according to how to detect the short circuit or grounding of the knife switch distribution line under the protection of no circuit breaker and leakage circuit breaker; (actually, if there is a short circuit on the knife switch distribution line, the consequences Either the wire is blown or the knife switch is burned out. However, I still answer the question according to the detection principle). (1) Turn off the power switch at the beginning of the power distribution line, disconnect all load switches on the line, including the plug-in load plugged into the socket, and use a multimeter resistance × 100 to measure the two outlets at the outlet end of the power switch. Resistance value, if the resistance value of the multimeter is measured to be very small (that is, the pointer swings to the right almost to the end), it proves that there is a short circuit between the phase line and the neutral line, otherwise there is no short circuit. It is also the same detection method to measure whether there is a short circuit between the phase line and the protective ground (zero) line, and the neutral line to the protective ground (zero) line. (2) If there is no short circuit between the phase line and the neutral line, the phase line to the protective ground (zero) line, and the neutral line to the protective ground (zero) line, you can check whether there is a grounding phenomenon between the phase line and the neutral line.
If you have a clamp meter on hand, it is best to use a clamp meter to detect the ground current. The detection method is: first disconnect the power switch, remove the power distribution zero line from the outlet of the power switch (and mark it), and then Turn on the power switch, and use the clamp meter to measure whether there is grounding current in the phase wire (if the clamp meter is set to the 100A gear, if the current cannot be measured, then slowly dial to the lower current gear), if the grounding current is still not detected , you can rule out the grounding of the phase line. After detecting the phase wire, turn off the power switch to remove the phase wire, connect the neutral wire to the phase wire outlet contact of the power switch, close the power switch and use the above clamp meter to measure the phase wire to detect the neutral wire. If you don't have a clamp meter at hand, you can also find a chandelier head and an incandescent bulb of about 25 watts, install the lamp head, and connect two wires of about 15 cm for use. The detection method is: disconnect the power switch, remove the phase wire and neutral wire, first connect the lamp holder and the bulb in series between the phase wire and the phase wire outlet contact of the power switch, and then close the power switch after taking safety measures. If the bulb is on, it proves that the phase line is grounded. The higher the brightness of the bulb, the greater the grounding current, and vice versa. If the bulb is not on, it can be ruled out that the phase line is grounded. After testing the phase wire, turn off the power switch, remove the phase wire, connect the original bulb in series between the neutral wire and the phase wire connection point at the outlet end of the power switch, and after taking safety measures, turn on the power switch to detect The detection result of the zero line is also the same as that of the above-mentioned detection phase line.
