How to use a multimeter to measure the continuity of lines that are under power
In electrical engineering and electric drive, electricity is divided into weak electricity, strong electricity, and low voltage, high voltage, and extra high voltage. However, weak electricity includes strong electricity or even high-voltage electricity, such as televisions, switching power supplies, and LED light power supplies. The electricity can be as weak as a few volts and as high as more than 10,000 volts. High voltage includes low voltage and weak current, because the control system controls low voltage to control high voltage, and weak current controls low voltage, for the sake of operational safety.
If you simply use a multimeter to measure the continuity of live lines, I don't agree! You can use a voltage test pen to measure whether there is electricity, or you can use an ohm block to measure the quality of the circuit after the power is turned off.
Electrician is a high-risk industry, and sometimes it is necessary to measure data. Without electricity, there is no way to measure the actual data voltage and current. and waveform graph. Live measurement is also a live work. Although there are labor protection supplies, insulated gloves, and insulated shoes, it is really inconvenient for the guy to bring them to work. Friends, tell me the work is difficult!
As for how to use a multimeter, you can read the manual and go to Baidu. Everyone's answers are very good, so I won't repeat them. What I want to express is the precautions for live measurement, how to work safer and use the multimeter more safely.
1. Live measurement of weak current
When measuring, do not blindly measure first. Check the weak current and strong current in the circuit. Select the right gear. There is basically no danger in measuring voltages below DC and AC24V. However, do not touch the mains power and the high-voltage part of the equipment, and Large capacitance.
When measuring high voltage in low-voltage equipment, the best way is to first cut off the power, discharge (including capacitance), then select the gear of the test pen, place the measuring point, then power on, and read the measurement data. The digital multimeter has a memory button. , you can press the memory key, which will be safer.
When a multimeter is used to measure the voltage while the power is on in the factory, if there is voltage, the line may not necessarily be connected, and if there is no voltage, the line must be blocked.
Because it is a live measurement, there is a transformer in the line, a motor exists, there is electricity at the breakpoint, and there is electricity under the breakpoint. The electricity at the breakpoint is the power supply, and the electricity under the breakpoint is the electricity from another phase through the winding or coil. , be sure to pay attention to this phenomenon. Therefore, using a multimeter to measure the continuity of a line while it is powered is not accurate! For mains power, it should be single-phase power. If the live wire is disconnected, there will be no power supply, but if the neutral wire is disconnected, there will be a phenomenon of power but no voltage.
To sum up, it is correct to use a multimeter to measure the continuity of the circuit while the circuit is powered on. Otherwise, it may get bypassed by yourself. The best way is to use an ohm block after powering off, or use a megger to measure the continuity of the circuit more accurately.
