How to Use a Multimeter to Check the Circuit? Methods of Using a Multimeter to Check for Leakage in the Circuit
A multimeter has a buzzer range. That is, when using the two test leads to measure the same wire, if there is a short circuit, there will be no response; if it is a continuous path, there will be a buzzing sound. Sometimes, when the equipment itself has a live outer shell due to poor grounding, you can use a multimeter. Place the red test lead on the outer shell and the black test lead in direct contact with the ground, and you can measure the electrical strength of the outer shell's leakage, which allows you to have a better understanding of the remaining work. Similarly, it can be connected in series to the circuit to measure the AC and DC current.
To check whether the circuit is leaking electricity, a megohmmeter (insulation resistance tester) should be used because the voltage of a multimeter is relatively low (9V), while the voltage of a megohmmeter is relatively high, 500V. Since the operating voltage of the circuit is 220V, it is difficult to diagnose a circuit with unobvious leakage. If you want to use a digital multimeter to check for circuit leakage, first cut off the power supply, discharge the circuit, and then use the resistance range, specifically the 2M range for measurement. The normal display should be 1 (infinite).
To measure whether the circuit is in a connected state, you can use the ohm range of the multimeter for measurement. When measuring, you need to select a position where the pointer of the multimeter is close to the 0 ohm range. If the circuit is in the electrical circuit, connect one end (end A) of the circuit to the multimeter (red test lead) at the 100 ohm range, and connect the black test lead to the other end (end B) of the circuit to be measured. If the measurement result is zero, it indicates that the circuit is connected, also known as a continuous path. Only when there is a continuous path can current flow through the circuit. If when measuring from end A to end B of the circuit, the pointer of the multimeter's ohm range is not close to 0 ohms, the circuit is already in an open circuit state. An open circuit is also called a break or an open.
A multimeter can easily find out the cause of the leakage.
Fault Finding and Analysis
First, ask the user who reported the repair about the fault phenomenon and any obvious characteristics. Secondly, observe whether there are any intuitive fault points on the surface, and then proceed to the next step of inspection.
First, disconnect the main isolating switch of the user's power supply incoming line and turn off all the user's electrical loads, such as pulling out the refrigerator plug and turning off the water pump switch, etc.
Set the digital multimeter to the 200M range of the ohm range. Place one test lead on one of the two outgoing lines on the load side, and touch the other test lead to the wall. It is best to touch the grounding wire or a temporary grounding wire. After the number displayed on the multimeter stabilizes, read the insulation resistance value of the main circuit. If the insulation resistance value is less than 0.5 megohms, there is a problem with the main circuit. If the insulation resistance is above 0.5 megohms, you can rule out that there is a problem with the main circuit. Use the same method to measure the other wire and check the value to see if there is a problem with the main circuit.
Check the insulation resistance values of the branch circuits and each electrical appliance. Also, use the same method to detect them one by one until the fault point is found.
Operation Precautions
When using the 200M range of the multimeter's ohm range, pay attention not to touch the metal parts of the test leads with your hands during the measurement, as this will make the reading inaccurate.
When measuring each electrical device, pay attention to discharging it first to prevent the capacitive current in the electrical device from hurting people.
This method is a relatively safe way to find the fault point in a power-off state. This method is also applicable to the search for faults in power users and factory building leakage. However, when searching, not only should the power supply incoming line be disconnected, but the neutral line should also be disconnected to avoid electric shock accidents.
