Method of judging short circuit, open circuit and leakage by multimeter
The method of multimeter to judge short circuit, open circuit and electric leakage is:
Short circuit: disconnect the power supply and measure the resistance. When the resistance is very small or even 0, it is a short circuit (metallic short circuit);
Open circuit: disconnect the power supply and measure the resistance. When the resistance is infinite, it is open circuit (open circuit).
Leakage: connect the power supply and measure the voltage of the shell to the ground. When the voltage value is large, it is leakage; Measure the current difference between live wire and neutral wire. If it is not 0, it will leak.
The above is the principle of multimeter to judge circuit fault, but there are some differences in actual circuit fault judgment.
Next, let's take a look at how to use multimeter to judge the short circuit, open circuit and leakage in the actual circuit.
1. Summary
The picture below is my summary of the method of checking short circuit, open circuit and leakage with multimeter, which can be saved for future use.
2. multimeter to determine short circuit (220V circuit, for example)
(1): Disconnect the circuit power supply.
(2): Cut off the circuit breakers of each branch of the circuit.
Objective: To eliminate the influence of branch roads on trunk roads.
(3): Measure the resistance between the live wires of the trunk line. If the resistance is 0, a short circuit (metal Xing short circuit) will occur in the trunk line.
Note: When it is determined that there is a short circuit in the main road, continue to measure the resistance between the terminals of other equipment on the main road. Determine the short-circuit points in turn.
(4): According to the same method as the trunk, find out whether there is a short circuit point in each branch.
Note: it is difficult to determine the short-circuit fault point of the circuit, but as long as we follow the circuit drawings,
Divide the circuit into small pieces according to the main branch, and measure the resistance value patiently, and everything will be solved.
3. multimeter to determine the open circuit (220V circuit, for example)
The judgment of open circuit can be judged according to infinite resistance during open circuit,
But when the circuit is complicated, we can turn on the power supply.
Then determine the abnormal points (such as the indicator light is not on, or other equipment is working abnormally).
Measure the voltage to ground step by step according to the circuit drawings.
When the voltage of an element to ground is 0, it means that there is an open circuit before it, and continue to look up.
Until the breaking point is determined.
4. multimeter to determine the leakage (220V circuit, for example)
How to judge when the shell is charged;
Turn on the power supply of the equipment, and switch the multimeter to the AC voltage measuring range. One end of the two probes is connected to the equipment shell, and the other end is grounded to measure the voltage of the shell to the ground. If there is voltage, the shell is leaking.
How to judge when the line leaks electricity;
Because it is troublesome to connect the probe to the circuit in series when measuring the current with multimeter, we can use the clamp ammeter to measure the circuit current when conditions permit.
Turn on the power supply of the circuit, and pass the neutral live wire of the main line side by side through the clamp ammeter. If there is no leakage, the current is zero. If there is leakage, the current is not 0.
Divide the circuit into several sections and measure them section by section. Until the leakage point is determined.
