Such protective devices (in regulatory documents they are designated VDT, which stands for differential current switches) should be installed in any residential buildings, whether it be an apartment in a high-rise building or a cottage. The wrong choice of RCD can lead either to false alarms of the device (which will become a constant headache for households), or inertness in the event of an emergency situation, and, as a result, electric shock.
What to consider when buying a product for your apartment, what parameters to focus on - we will discuss all these details.
RCD selection criteria
If the device is bought for a private house, then the choice becomes more complicated for several reasons. For example, in connection with the peculiarity of connecting the site to industrial / voltage. Therefore, further - in relation to a city apartment.
Type of power supply
Everything is simple here. RCD for 4 poles - for three-phase circuits, for 2 - single-phase. The last option for intra-apartment wiring is the best.
Rated current
VDT is always installed in series with another protection element - a circuit breaker (AB). Approximate for the apartment are shown in the figures.
Here is the machine, which is included in the same line with the RCD, and you should be guided. In articles devoted to the topic of choosing a VDT, there are often recommendations that its current rating should be equal to the similar characteristic of the AB, no less. The author does not agree with this.
The fact is that the circuit breaker is somewhat inert, so the current rating of the RCD must be higher than the similar characteristic of the AB. Why is excess necessary? If both the machine and the VDT are of the same rating, then during the time that the first works, the second may fail, especially if it is not from a well-known manufacturer. There are precedents.
Therefore, it is better not to experiment and choose an RCD with a parameter one step higher than that of AB. Usually, VDTs for 30 - 32 A are purchased for an apartment.
If it is being repaired and it is planned to install automatic machines on each line, then the nominal value is determined by the maximum possible load. In particular, which household appliance will be connected. All the necessary data are reflected both in the passport for a specific product and on the "nameplates" that are placed on the back wall of the case.
Current differential
It should not be confused with nominal. This is the leakage current from which the RCD is designed to protect. On the front panel of the product, this characteristic is indicated by I∆n (setpoint value). What to consider? There is such a thing - the current of non-release. That is, its meaning, in which a person’s hands are convulsed, and he is completely immobilized. The value is from 30 mA. Therefore, when choosing an RCD, it is necessary to pay attention to this characteristic.
For devices that will be connected to lines laid in rooms with normal humidity, this value is quite enough. And if with excess (for example, kitchen, bathroom), when the probability of damage increases, then it is necessary to focus on products with I∆n per 10 mA.
It is desirable to connect appliances such as a dishwasher, washing machine, hob with a separate cable. It is in this line that the RCD is 10 and turns on. In cases where wiring is carried out in the apartment, for example, from a common route to rooms with different humidity, then it is allowed to install a VDT of 30.
More details on the requirements for installing an RCD in an apartment can be found in SP31-110 of 2003 (section A, clause 4.15).
RCD type
AS is the most common choice. These react to instantaneous changes in alternating current (its leakage). The designation on the case is either letter or symbol.
A - it is recommended to include in the chain of household appliances in which there is a lot of electronics: TV, PC, complex units with program control. By the way, if you carefully read the instructions for such products (installation section), then you can find a recommendation on the type of RCD. Symbol
B - you should not pay attention to such RCDs. They are not for home use.
In residential buildings, the installation of VDT types A and AC is allowed. The choice of a specific model depends on what equipment will be connected to this line.
Operation principle
Electronic
The only plus is the lower price. There are enough cons. The main one is the dependence of the RCD on the “quality” and uninterrupted power supply. One of the problems of high-rise buildings is the regular “burning out of zero”. This happens when one of the apartment owners tries on their own, without professional knowledge and practical experience, to redo (install, change) something in the access power shield. You can also add a manufacturer. Electronic RCDs "made in China" do not last long.
El/mechanical
Such devices are somewhat more expensive, but much more reliable in operation.
You can determine the type of RCD according to the scheme that is applied to its case.
RCD selectivity
Simply put, this is the turn-off delay.
No selectivity
In fact, this is the first stage of protection against electric shock. Such RCDs must be installed on each line.
Type S
Delay device. The time can be from 0.2 to 0.5 sec. These RCDs are often called fire-fighting ones, since they are mounted after the introductory AB. Their purpose is to protect the entire apartment from overvoltage, which often leads to ignition of electrical / wiring. The recommended setting parameters are from 100 to 300 mA.
Why is the delay needed?
If you install 2 RCDs in series in the line (the first and second stages of protection) with the same response time, then after eliminating the malfunction, you will have to go out into the entrance, open the shield and turn on the VDT at the entrance to the apartment. And if you consider that you need to look for a flashlight (which often happens, since the light on the site is not always on, or there is none at all), there is little pleasure in this.