How to use a multimeter to check short circuit, open circuit and leakage?

Learn to use a multimeter and you don’t have to worry about home wiring failures.

The multimeter is one of the most commonly used tools for electronic circuit personnel. It is indispensable when testing electronic circuits. With a multimeter, faults can be quickly located. Although the multimeter is small in size, it has powerful functions. It can measure resistance, capacitance, diodes, transistors, DC voltage, AC voltage, current, etc. Finding short circuits, open circuits, and leakage is the most basic function of a multimeter.

How to find a short circuit using a multimeter?

Short-circuit measurement is very common in electrical appliance maintenance and component fault location. When measuring short-circuit faults, be sure to disconnect the power supply and remember not to operate with power on. Short-circuit measurement uses the beep or ohm range of the multimeter. It is more intuitive to use the beep when the circuit is short-circuited. The multimeter will directly "beep" when the circuit is short-circuited. The principle of the beep range is that when the measured resistance is less than about 75Ω, the multimeter will beep. If you want to know the resistance between the two circuits more accurately, you can use the 200Ω range for measurement. When using the beep range for measurement, sometimes the actual internal resistance between the two signals is small, so it is easy to misjudge. For example, the relay/contactor coil, many relay/contactor coils have an impedance less than 75Ω. When using the beep range for measurement, it will beep and think that there is a short circuit, but in fact there is no short circuit.

Engineers often use the beep mode of a multimeter to quickly find short-circuit fault points in circuits or components, such as measuring whether resistors and capacitors are short-circuited, whether diodes are reverse-broken, whether transistors are broken down (when transistors break down, the base and emitter are usually short-circuited), whether the power supply and ground of an integrated circuit chip are short-circuited, whether two pins are short-circuited, etc.

How to use a multimeter to find a short circuit?

How can a multimeter determine whether the circuit is open? Use the multimeter beep function to measure the two ends of the circuit. If the circuit is intact, the multimeter will beep. If the multimeter does not beep, it indicates that the circuit between the two test leads is open. Note: The power supply must be cut off for open circuit measurement, and it cannot be operated with power on.

If you use a multimeter to check if the home circuit is broken, but the two wires are not in the same place, for example, one end is the bedroom socket and the other end is the main switch in the living room. The distance is far, and the test lead is not long enough, what should you do? You can extend the wire for measurement. If there is no buzzing, it means that the circuit between the two ends is broken. Find the connection point between them, narrow the range and measure step by step.

How to use a multimeter to find leakage?

Leakage current measurement mainly detects whether the live wire, neutral wire and wall are well insulated, and whether the power line (live wire, neutral wire) and the metal casing of the electrical appliance are well insulated, such as the metal casing of refrigerators, induction cookers, microwave ovens, electric kettles, etc.

1. Under normal circumstances, the surface insulation of the live wire and the neutral wire is good, and the resistance between them and the wall is generally more than several MΩ, and the minimum resistance should be 0.5 MΩ to be qualified. Measurement steps: ① Cut off the main power switch to ensure that the power is disconnected; ② Use the 20MΩ ohm range of the multimeter to measure; ③ Connect one probe to the wall, and the other probe to the live wire and the neutral wire to measure the impedance between them and the wall. If the impedance is less than 0.5 MΩ, it means that the wire has leakage, which may be caused by the wear of the wire or the poor wrapping of the connection. It is best to check the line.

2. The principle of measuring whether the metal casing of an electrical appliance is leaking is similar. Turn off the power and use the 20MΩ ohm range of a multimeter to measure. Connect one probe to the casing and the other probe to the power cord (live wire, neutral wire) to measure the impedance. Under normal circumstances, it should be above 0.5MΩ. If the impedance is smaller, it means there is leakage.

Summary: Learn to use a multimeter to find short circuits, open circuits, leakage and other faults. When your home line encounters a fault, you can do it yourself. Remember: When measuring short circuits and open circuits, do not operate with power on.