Electrical wiring in the broader sense of this term is the same mandatory engineering system of a modern home as plumbing, ventilation and sewerage. Due to the peculiarities of the effect of electric voltage on the human body, the wiring belongs to technology increased danger and during its creation, special measures are taken, one of which is the installation of a differential machine or RCD. This compact device is extremely useful in that it protects users against so-called leakage currents, which occur when the insulation resistance drops without short-circuiting.
Currently, many residential property owners create or overhaul electrical wiring themselves. This approach, on the one hand, allows you to save a lot of money and makes you feel like a real master, on the other hand, it does not require significant costs for a technological tool. In addition, modern electrics are extremely user-friendly and the installation process itself is not very complicated.
In the process of installing an RCD, with a lack of experience, mistakes are made. What are they all about?
Application at the input of a sensitive RCD
RCDs available on the market differ in response threshold. In an effort to achieve a higher level of protection, 30mA RCDs are sometimes installed directly at the input, which then leads to its frequent operation, especially when you turn on any powerful load.
Figure 1 demonstrates this phenomenon in schematic form, and its physics lies in the fact that the insulation resistance of even a serviceable wire is finite, i.e. leakage current always exists. Moreover, as the length of the line increases, it increases at a rate of 0.04 mA / m. With a 200 meter average home wiring length, this gives 8 mA of leakage. If we also take into account the leakage in switches, sockets and other "point" elements of 0.4 mA from each ampere of current consumption, we get a calculated value of 15 mA.
According to the application A1.2 of the rules of SP 31-110-2003 for the stable operation of the RCD, the quiescent leakage current should not exceed one third of its operation current. In our case, this is 15 × 3 = 45 mA. It follows from this that at the moment of turning on a powerful load, the peak value of the current exceeds the threshold tripping, the RCD perceives this as an emergency and disconnects the protected circuit, i.e. apartment entirely.
Rule: the input must be set to 100 or 300 mA RCD.
Connection of neutral wire and bus after output from RCD
A configuration that assumes a direct connection of the neutral conductor to the exposed part of the wiring is shown at the top of figure 2. It is easy to guess that in this case, the entire load current connected to the outlet will be perceived by the RCD as a leakage current, which will lead to its operation.
The correct wiring diagram is shown at the bottom of Figure 2.
Rule: the neutral wire of the beam after passing the RCD with other neutral wires does not contact or zero and the phase is taken only from the RCD output.
Using an RCD without a machine
Many users consider the RCD to be an improved version of the machine, in justification of which they point to the marking of the current value that is applied to the case of this device. In fact, we are talking about devices with different functional purposes: the machine protects the wiring from short circuits and overloads, while an RCD protects from leakage currents. Thus, they complement each other, are included in series and one cannot do without one of them.
Important! Of the two wiring options shown in Figure 3, the bottom one is correct.
Switching errors
The dashboard contains several automatic devices and RCDs, and the dashboard itself is quite compact in size. These features increase the probability of connection errors between individual machines and RCDs. Zero and phase are conducted by wires of different colors, so the most common mistake here is connecting neutral and phase wires from different RCDs to the load, as shown in Figure 4. The operation of an RCD is based on a comparison of the magnetic fluxes created by currents flowing through different wires. It is clear that with such an error, the risks of false operation of at least one of the RCDs become so great that they make it impossible for the normal operation of the wiring.
Conclusion
Modern RCDs are well developed in terms of technology, perfectly perform their functions and reliably protect the wiring from leakage currents. To ensure their normal functioning and the absence of false alarms, it is enough to observe a few simple rules and carefully perform the installation.