The selectivity of residual current devices (RCDs) is a very important part of the installation, which is extremely useful when a fault is detected. It then switches off only the circuit in which the fault occurred. This ensures that the rest of the electrical installation remains in normal operation. People who design safe, fully functional electrical systems and networks must remember this. In this article, we will deal with this topic in detail, discussing the following issues: is the selectivity of residual current devices a necessity, what conditions must the circuit breaker meet to achieve full selectivity, and the most common mistakes made when selecting equipment. We invite you to read!
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Is selectivity of differential circuit breakers a necessity?
Residual Current Devices (RCDs), commonly known as differential switches, are extremely important safety devices that protect against electric shock. They also prevent damage to electrical installations.
They detect even small differential currents, which can be created when current flows through the human body or as a result of a short circuit between the installation and the ground. The selectivity of the differential switch is important here, because it refers to the cooperation of several differential switches in one electrical circuit. The role of selectivity is therefore invaluable here.
Selectivity of differential circuit breakers is not always required, however, its use significantly increases the level of safety, as well as the comfort of using the electrical installation. Its lack can therefore lead to undesirable situations, for example, when a failure of one circuit leads to a power cut in other circuits. This is particularly irritating in industrial facilities, public utility buildings or multi-storey residential buildings.
The use of selectivity eliminates such situations because in the event of a short circuit, only the circuit in which the damage occurred is disconnected. Other installations operate normally, which minimizes power outages, increasing the overall efficiency of the system.
What conditions must a residual current circuit breaker meet to achieve full selectivity?
The differential switch, also known as a differential switch , plays a very important role in the entire installation, especially in selectivity, which ensures automatic disconnection of the power supply to the appropriate circuit. Its use is therefore perhaps not a necessity, but a highly recommended action.
Let us also remember that a residual current circuit breaker must meet several important conditions to guarantee full selectivity. When selecting a differential circuit breaker, we must therefore bear in mind the issue of tripping times and the values of differential currents. The circuit breakers must be installed so that those placed higher in the system hierarchy react slower (and to a higher current) than those lower. This is important because it prevents several devices from tripping simultaneously at the same time. Therefore, a residual current circuit breaker with different time-current characteristics should be selected.
It is also worth paying attention to the compatibility of the characteristics of the installed devices, as well as the appropriate short-circuit protection. This reduces the frequency of false shutdowns of receivers, ensuring the proper operation of the entire system.
The most common errors in the selection of electrical equipment in the context of selectivity
When designing an electrical installation, including selective residual current circuit breakers, we must avoid errors so that the modular and electrical equipment is properly matched. Otherwise, it may malfunction.
One of the most common mistakes is ignoring the differences in RCD tripping times. This happens when all the breakers have the same characteristics. It can happen that they trip simultaneously, thus cutting off the power supply to the entire facility.
Another serious mistake is selecting the wrong value of the differential current, which can result in excessive or too rare trips. An improper analysis of the operating conditions, for example the presence of non-linear devices, can also have disastrous consequences.
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