What does a multimeter show when a line is grounded or shorted?
In the case of power failure with a multimeter 10k gear, the load is also disconnected, the line measurement. Three-phase four-wire, four lines of the resistance value of the multimeter display should be infinite, single-phase lines should also show a normal infinity, there is a resistance value can be determined when the line there is a short circuit. The determination of grounding, with a multimeter a pen contact a line end, with another pen to the ground measurement of resistance changes, infinity is normal, and vice versa there is a grounding phenomenon, and all the lines with this method of measurement one by one, to find the problem, in addition to pay attention to if it is a steel cable, the other end of the pen on the steel belt measurements. In order to ensure the accuracy of the measurement, it is best to check whether the line is the existence of the phenomenon of disconnection, and then use a multimeter to check the continental short circuit and grounding faults. In fact, troubleshooting these two kinds of faults, you can also use megohmmeter, detector and other tools to make the repair faster and more accurate.
Lighting appliances as an example: lighting appliances are a fire wire, a zero wire, a ground. If the fire wire and zero line short circuit, the air will be tripped, then turn off all appliances, from the air open to take down the output of the two wire, (the user line of fire and zero head) with a multimeter OuMu file to measure the resistance of the two lines should be infinity, if the value of zero or only a few ohms is the fire wire and the zero line is short-circuited.
Open the air, the output line of the two heads do not install, turn off all electrical appliances, with a multimeter AC two hundred and fifty gear measurement: a pen connected to the empty fire head, a pen connected to the user head, if there is a voltage of about two hundred volts to prove that the line is grounded.
In China's low-voltage power system, the neutral point must be grounded, the neutral line can not be used as a local line, must be equipped with a special protective ground line. Into the user's electrical box after the fire wire and the zero line must remain insulated from the earth to work properly. When the resistance of the fire wire or zero wire to ground is less than 0.5M ohms, leakage protection action trip, cut off the power supply.
Trip occurs, you can use a multimeter to detect to detect the circuit breaker behind the line and the load is short-circuited or grounded. The method is as follows.
Disconnect the main power switch and disconnect the zero line from the power supply. (Some circuit breakers in the zero line is not open in the position of the breakers, you must remove the zero line), and then, with the multimeter's maximum resistance file (range must be greater than 1M ohms), respectively, to measure the fire line, the zero line resistance to ground, resistance such as less than 0.5M ohms, it is judged to be unqualified.
If, the fire wire, zero line resistance to ground qualified, that is not a ground fault. Then you can only use a multimeter to measure the resistance of the firewire and the zero line (you must unplug all, and close all appliances), the same must be greater than 0.5M ohms. If the line is not a problem, it is more troublesome, the problem is in the electrical appliances. Check them one by one!
Whether it is a short circuit or leakage of air will certainly trip, short circuit is not yet tripped the consequences, or a small nest may be a fire to solve the problem. In the family encountered such a situation must not close the gate again, first go to troubleshooting. First of all, the tripping of the air open all the corresponding loads are thrown off, and then in the air open the end of the zero fire line all apart, with a multimeter to measure whether there is a path between them, with a multimeter beeping block will sound short-circuited, short-circuited with a resistance file resistance will show zero ohms, if there is a short-circuit phenomenon to find the line.
Find all the connectors and junction boxes in the line after this open, whether the joint insulation is not good, and then resistance measurement method in each connector and junction box with a multimeter check. The reason is that the short-circuit moment generates a high current air open automatically tripped, the line will not burn how much general conditions in the joints or junction boxes to resistance measurement method is able to determine the location of the short-circuit.
Then it is the line leakage check to resistance method of measurement, with a multimeter pen connected to the fire line or zero line, a pen grounded, the normal situation is the resistance is infinite, if there is resistance or resistance is very small, that measured the existence of this line grounding phenomenon. The premise is to ensure that the line does not exist short-circuit phenomenon, otherwise it is not judged.
