Troubleshooting Shorts, Opens & Leakage Using a Multimeter
Short circuit "refers to the direct connection of the two ends of the power supply by wires. Using a multimeter to check for a short circuit is actually determining whether the circuit is connected or not by measuring the resistance. Due to the fact that the resistance range of a multimeter cannot be measured with power on, the resistance measurement must be carried out with power off.
Judgment method: First disconnect the power supply to ensure there is no power, then use the resistance range of the multimeter to measure the two ends of the object being tested. Under normal circumstances, there is a certain resistance value. If the measured resistance is zero, it indicates that the object being tested has a short circuit. You can also use the buzzer or diode mode of the multimeter to measure the two ends of the object being tested in the event of a power outage. If a sharp buzzing sound is emitted, it indicates that the object being tested has a short circuit.
Attention: If the measured resistance has a certain value but is very small, it is also likely that a short circuit has occurred, which is caused by contact resistance. We sometimes encounter this situation when measuring, for example, if you press the multimeter probe tightly, the measurement result will become smaller; Relax the pen a bit, the measurement result will become larger. This is because the probe and the tested wire were not connected properly, and the contact resistance at the connection point was also measured. In order to minimize measurement errors and restore the authenticity of the results as much as possible. So when measuring, the probe and the wire of the measured object must be tightly connected; If the tested wire is severely corroded or oxidized, the oxide layer on the surface of the conductor should be scraped off. (Under normal circumstances, copper appears bright golden yellow, but after oxidation, it appears dull black; the same applies to aluminum wire.)
Check for open circuit with multimeter
After knowing how to use a multimeter to measure short circuits, measuring open circuits becomes very simple.
Judgment method: First, disconnect the power supply to ensure there is no power, and then use the resistance range of a multimeter to measure the two ends of the circuit being tested. Under normal circumstances, the resistance is zero or has a certain resistance value. If the measured resistance is infinite, it indicates that the two ends of the circuit are not connected, that is, a circuit breaker has occurred. You can also use the buzzer or diode mode of a multimeter to measure the two ends of the circuit when there is a power outage. If a buzzing sound is emitted, it indicates that the line is connected; On the contrary, if there is no sound, it indicates that the tested circuit may have a short circuit.
Attention: Under normal circumstances, the resistance at both ends of the wire is zero (or close to zero); Under normal circumstances, electrical equipment has a certain resistance value, but the specific resistance value depends on itself. So to determine whether the circuit or electrical equipment is broken, it is best to use a large range resistor. Because some electrical devices have high resistance values, such as energy-saving lamps, which cannot be measured with a small range.
