Method for Judging Short Circuit, Open Circuit, and Leakage with a Multimeter
The method for judging short circuit, open circuit, and leakage with a multimeter 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 an open circuit (open circuit)
Leakage: Connect the power supply and measure the voltage between the shell and the ground. When the voltage value is high, it is considered leakage; Measure the difference between the current flowing through the live wire and the zero wire. If it is not 0, there will be leakage.
The above is the principle of using a multimeter to determine circuit faults, but there are some differences in actual circuit fault diagnosis.
Next, let's take a look at how to use a multimeter to diagnose short circuits, open circuits, and leakage in actual circuits.
1: Summary
The following picture is my summary of the methods for checking short circuits, open circuits, and leakage with a multimeter. It can be saved for future use.
2: Using a multimeter to determine a short circuit (220V circuit as an example)
(1) : Disconnect the circuit power supply.
(2) : Cut off each branch circuit breaker of the circuit
Purpose: To eliminate the impact of branch roads on main roads.
(3) Measure the resistance between the zero lines of the live wire on the main circuit. If the resistance value is 0, a short circuit (metal Xing short circuit) occurs in the main circuit.
Note: After determining the existence of a short circuit in the main circuit, continue to measure the resistance between the wiring terminals of other devices on the main circuit. Identify the short circuit points in sequence.
(4) Follow the same method as the main road to check for any short circuit points on each branch.
Attention: It is difficult to determine the short-circuit fault point of the circuit, but as long as we follow the circuit diagram,
By dividing the circuit into small pieces based on the main and branch roads, and patiently measuring the resistance value, everything can be easily solved.
3: Multimeter judgment for open circuit (220V circuit as an example)
The judgment of open circuit can be based on the infinite resistance during the open circuit,
But when the circuit is more complex, we can turn on the power supply,
Then identify the abnormal points (such as the indicator light not working, or other equipment working abnormally),
Measure the voltage to ground step by step according to the circuit diagram.
When the voltage to ground of a certain component is 0, it indicates that there is an open circuit before it, and continue to search upwards.
Until the breaking point is determined.
4: Judging Leakage with a Multimeter (Taking 220V Circuit as an Example)
How to determine when the shell is live:
Connect the device power supply, switch the multimeter to AC AC voltage measurement mode, connect one end of the two probes to the device casing and the other end to ground, and measure the voltage between the casing and ground. If voltage is present, it indicates that the casing is leaking.
How to determine when there is a leakage in the circuit:
Due to the inconvenience of connecting the probe in series to the circuit when measuring current with a multimeter, we can use a clamp type ammeter to measure the circuit current when conditions permit.
Connect the circuit power supply and pass the zero and live wires of the main line side by side through the clamp ammeter. If there is no leakage, the current is zero. If there is a leakage situation, the current is not 0.
Divide the circuit into several sections and measure each section. Until the leakage point is determined.
