How to use a multimeter to check if the circuit is short circuited or grounded?
If you want to check the circuit for short circuits. Firstly, cut off the power supply to the circuit, and then open each load switch. Use the ohmmeter to measure the resistance between the two wires. Under normal circumstances, the greater the resistance, the better. If you want to determine whether the circuit is grounded or not, you can use the ohm range of a multimeter. To measure the resistance of each circuit to ground. The bigger the better. It should be pointed out that using a multimeter to measure the presence of short circuits and grounding in a circuit is inaccurate. It should not be, if the grounding or short circuit resistance is very small, it can be detected with a multimeter, if the resistance is slightly higher. A multimeter cannot be checked, in the 380V low-voltage circuit. A 500V megger should be used for measurement, whether between lines or to ground. It should be above 0.38 megaohms. Otherwise, it is unqualified.
Firstly, it is necessary to separate the live line and the zero line.
Ground wire: Set the multimeter to the AC voltage range and the range is higher than 220V. Insert the red lead into the voltage hole, but not the black lead. Then, insert the red lead into one of the sockets and observe the reading.
The line with the highest reading is the live line, the line with the lowest reading is the zero line, and the line with the lowest reading is the ground line.
If two readings are small and one reading is large, it indicates that the ground wire is not grounded and the ground wire is also connected to the zero wire. The second step in the future does not require further measurement.
Turn the multimeter to the "short circuit" test function (if there is no resistance test), and connect the red and black probes to the ground of the circuit and the ground of the mains. If the test result is a short circuit or the resistance is very low, the circuit is grounded, and vice versa.
Check for leakage and grounding, and set the multimeter to 200M. For example, when measuring equipment insulation, connect one end of the probe to the equipment casing or ground wire, and the other end of the probe to the circuit. When measuring insulation, do not touch the probe with your hands to prevent measurement errors.
Adjust the resistance range of the multimeter to 20K or 200K, turn off the main power supply and load power supply, use one lead of the multimeter to connect to the live wire and one lead to connect to the ground wire, check the resistance value, and then connect one lead to the zero wire and one lead to connect to the ground wire. Observe the resistance situation twice. If there is a resistance value above 7.3 or above 14, it indicates that the live wire or zero wire with the resistance value is leaking.
Many electricians will tell you to cut off all power and measure the resistance between two wires using the smallest resistance range (or diode range) to see if it is close to 0 ohms (or if the diode range shows 0). If it is close to 0, it can basically be determined that the two wires are short circuited together. Similarly, measure this wire to ground to see if it is in the same condition. If it proves that this wire is grounded, this method is of course feasible, It's just that in practical work, it's not convenient to cut off power in many places. Is it feasible to continuously measure electricity?
The essence of voltage is the potential difference. As long as the voltage between two lines is 0, a resistance range can be used to measure:
1. Assuming that there is a short circuit between lines A and B to be measured, there may be a voltage (such as 220 volts) between lines A and B to the zero line. The potentials on their lines are potential A and potential B. Many people first think that if they measure directly with a resistance level, the power supply on lines A and B must be disconnected separately before measurement can be made. This idea is not wrong, it can only be said conservatively.
2. Directly set the multimeter to the AC voltage range, select the highest range, such as AC1000V, and then use the AC voltage range of the multimeter to measure line A and line B. If there is a relatively high voltage (such as 200V) between the two lines, it can be proven that potential A and potential B are not equal, that is, there is a voltage difference between potential A and potential B. These two lines are not equipotential and are not shorted together.
3. If line A and line B use an AC voltage range to measure without voltage, for the sake of safety, a DC voltage range such as 1000 volts is selected to measure between them and confirm that there is also no DC voltage. This can prove that potential A and potential B are equal. Note that equality does not mean they have no voltage to zero line N. For example, line A and line B are both 220 volts to zero line N, but the voltage between them is also 0 volts. At this time, You can use the smallest resistance range to measure the resistance between these two wires. If it is close to 0 ohms, it indicates that these two wires are shorted together.
4. As for whether to measure grounding, the above method can also be used for simple measurement. The idea is to understand the ground wire as a regular wire. However, in general, to measure whether it touches the ground, a megger can be used to measure the insulation resistance (usually 5 megohms for insulation). At this time, it is necessary to cut off the power to measure.
