Common Hazards When Using a Multimeter
The multimeter is connected in parallel with the tested component, and the multimeter plays a shunt role, requiring a high internal resistance of the multimeter. In Figure 2, the multimeter is connected in series with the tested device to divide the voltage, and it is required that the internal resistance of the multimeter be small. Once connected incorrectly, such as in current testing mode, the multimeter is placed at both ends of the tested device. The circuit where the multimeter is located is short circuited due to the low internal resistance of the circuit, which may be caused by a blown fuse, posing a danger.
Another type is potential safety hazards, such as electric shock caused by accidental contact with live parts, transient high voltage caused by switch and load start-up, etc. With the increasing complexity of power distribution systems and loads, the possibility of instantaneous overvoltage has greatly increased. Motors, capacitors, power converters, frequency converters, and other equipment are the main sources of spikes. In addition, lightning strikes on outdoor transmission lines can also cause very dangerous high-energy transient high voltage. When measuring the power system, this instantaneous high voltage is often invisible, but it does exist and is difficult to avoid, and its potential danger is also greater. These situations are often encountered even in low-voltage measurements, and the instantaneous voltage generated can reach several thousand volts or higher. Therefore, when operating a multimeter, it is not only necessary to pay attention to correct wiring to reduce unnecessary danger or damage, but also to avoid potential hazards through some safety designs.
So what are the safety protection designs for multimeters?
The first type is external protection for multimeters, such as double-layer isolation insulation protective covers, probe anti contact protection, and insulation protection for plugs and sockets. But to avoid the harm caused by momentary high voltage, safety must be deeply integrated into the digital multimeter, in other words, there must be sufficient safety design inside the digital multimeter. Therefore, the International Electrotechnical Commission (IEC) has defined a new set of international safety standards specifically for testing instruments. Previously, the IEC348 standard was used, but it has now been replaced by IECl010. The safety indicators of a multimeter designed according to the new standard IECl010 are much higher than those designed according to IEC348.
