In which situations should a multimeter not be used or is it not recommended for use?
The multimeter is one of the most essential tools for electricians, due to its simplicity and practicality. It can be said that every electrician has at least one in their arsenal, with a huge inventory. It can test for continuity, voltage, current, and even some electronic components, seemingly omnipotent and possessing exceptional comprehensive capabilities. This is also the origin of the name "multimeter".
We often say that a multimeter can do this and that, and we always keep it handy during maintenance. But have we ever thought about situations where a multimeter is either useless or unusable?
Today, let's talk about the limitations of multimeters. Firstly, regarding current measurement, multimeters can indeed measure current, but they must be connected in series with the circuit when doing so. Otherwise, they cannot be used. Generally, attempting to connect a multimeter in series with a circuit for measurement is very unsafe when dealing with high currents. On the other hand, sometimes connecting in series requires dismantling the circuit, so multimeters are not very commonly or practically used for current measurement!
Secondly, it is to measure the insulation resistance of grounding, motor cables, etc. Because multimeters use batteries as their power source, the voltage is relatively low. However, the insulation resistance values of grounding, cables, motors, etc. are relatively high. Under normal circumstances, multimeters find it difficult to measure their effective resistance. Even if they manage to measure it, the results are usually subject to significant errors, or even incorrect values, lacking practical reference value and sometimes even misleading. Therefore, it is not recommended to use multimeters in such cases.
Another situation is when a multimeter cannot be used due to battery capacity issues. People often complain that their electric bike runs out of power after a short while even though it was just charged. They suspect that the battery might be broken. However, this so-called battery failure is actually caused by a decrease in battery capacity, and a multimeter is useless in addressing such issues!
