How to use a multimeter to check whether the circuit has a short circuit or a grounding fault?
As can be seen from the above, it is very convenient to use a multimeter to measure a short circuit, but it is not so accurate to use a multimeter to measure grounding. In fact, it is most reasonable to use a megohmmeter. Now, let me introduce to you how to use a multimeter to check whether the circuit has a short circuit or a grounding fault.
Let's first talk about short circuits. In fact, this question itself has some problems. We know that a short circuit in a circuit refers to the connection between phases or between a phase and the ground other than during the normal operation of the power system. Therefore, the grounding of a phase wire can also be regarded as a type of short circuit. If the neutral wire is grounded, a leakage current will be generated, and the leakage protector will trip. So, the question from the person asking is not very rigorous. Personally, I think what he wants to ask is how to detect a short circuit and leakage in the circuit.
How to use a multimeter to detect a short circuit in the circuit
First, cut off the power. Adjust the function switch of the multimeter to the buzzer range. Place the two test leads of the multimeter on the two terminals to be tested. If there is a short circuit, there will be a buzzing sound, and a very small conduction voltage value will be displayed. At this time, there is a short circuit between these two measured points.
Measuring the insulation of the circuit with a multimeter can tell whether the circuit has a short circuit. For example, when measuring the insulation of a single phase to the ground, if the insulation value is zero (metallic grounding) or very low (non-metallic grounding), it can be determined that this phase of the circuit is grounded. If it is not grounded, the insulation value is very high. Then measure the insulation between phases. If the insulation between phases is zero, it means that there is a short circuit between these two phases of the circuit.
Ensure that there is no electricity in the circuit. Use the resistance range (for an analog multimeter, set it to the RX10 range, and for a digital multimeter, use the continuity range that will beep). Touch the two test probes to the two points (or two wires) to be measured. If the pointer of the analog multimeter does not move, it is an open circuit, and if the pointer swings fully, it is a short circuit. For a digital multimeter, if it is an open circuit, the number does not change and there is no sound; if it is a short circuit, it will beep or the number will be zero.
Separate the wire cores at the two ends of the wire so that they do not touch each other. Then adjust the multimeter to the position mentioned above. Place the test leads on the wire ends of two different colors respectively. If the measured value is above 0.5 megohms or shows infinity, then the insulation of the circuit is okay, that is, there is no leakage in the circuit. If the measured result is below 0.5 megohms, then the insulation of the circuit is unqualified, and there is leakage. Check all the joints and junction boxes in the circuit after this air switch to see if the insulation of the joints is not done well. Then use a multimeter to check at each joint and junction box by the resistance measurement method. The reason is that a large current is generated instantaneously during a short circuit, and the air switch will trip automatically. Generally, the circuit will not be burned out too much. In most cases, the location of the short circuit can be determined by the resistance measurement method at the joints or junction boxes.
