Method for detecting short circuits in circuits with a multimeter
From the perspective of repairing electrical faults, short circuit faults have the following characteristics:
1. The resistance (or impedance) of the short-circuit point (i.e. both ends of the short-circuit) is zero or close to zero;
2. Short circuit circuits have great destructive power, and once a short circuit occurs, it is generally not possible to directly power on for inspection, unlike open circuit faults.
After a short circuit fault occurs, the protective components of the circuit (such as fuses, circuit breakers, etc.) act, and the protective components may control an area composed of multiple circuits. Therefore, when searching for electrical short circuit faults, it is necessary to first identify the faulty circuit from the faulty area, and then find the short circuit fault point in the faulty circuit.
1、 Method for Finding Short Circuit Fault Circuits
Generally, a multimeter method can be used to search, and the multimeter method is a method of measuring the resistance of a short circuit circuit circuit using the ohm range (resistance range) of a multimeter after the circuit is powered off.
Assuming that the fuse FU melts, it indicates that a short circuit fault has occurred in the area protected by the fuse, which includes 1-3 circuits and the main line. With the power disconnected, connect the melt of the fuse FU and place the multimeter in the Ohm position "R × 10 Ω "(do not place it in a multiple ohm range to avoid reading errors caused by human body resistance, etc.), connect it to the L and N terminals, and disconnect S1, S2, and S3 to disconnect each circuit. If the multimeter indicates zero resistance, it indicates that a short circuit fault has occurred on the main line.
If the multimeter indicates a resistance of "∞" or very high, the short circuit fault occurs in a circuit between 1 and 3. Close switches S1, S2, and S3 in sequence. If the multimeter indicates a certain value of resistance when S1 and S2 are closed, and zero resistance when S3 is closed, it indicates that the fault point is in the third circuit.
2、 Method for Finding Short Circuit Fault Points
After finding the short-circuit fault branch, it is necessary to continue to determine the specific location of the fault point. The short-circuit fault point must be at both ends or inside the voltage reducing components (such as bulbs, voltage type coils, motor windings, resistors, and other loads) in the circuit.
The method of point is to disconnect one end of the voltage reducing element R (shown in the figure as the bulb) and measure the resistance between 1 and 2 (i.e. both ends of the voltage reducing element) using a multimeter resistance gauge. If the resistance is zero, it indicates that the short-circuit point is inside this load; If the resistance is a certain value, it indicates that the load is intact internally and the short-circuit point is outside the load equipment. If the short-circuit point is external, measure the resistance between points 1-3. If the resistance value is zero, the short circuit fault is between wire 3 and wire 1.
By disconnecting certain points of these line segments and conducting measurements in sequence, the identified short-circuit fault point can be found.
