Modern wiring, which is compulsorily created in the housing stock and public buildings, refers to engineering systems of increased danger. To ensure normal operation, it must be supplied with a number of protective elements. One of them is an RCD, which de-energizes the wiring when leakage currents occur in it due to the drop in insulation resistance below a certain limit.
The industry produces several basic types of these elements, and in the process of self-construction or repair of wiring, the problem of their correct selection arises.
Varieties of RCD
The leakage current can have three main types, each of which is assigned a specific letter index.
If we are talking about ordinary alternating current, which occurs with linear loads, then its characteristic feature is the equality or slight difference in the amplitudes of the positive and negative half-waves. An RCD designed for such currents belongs to the AC type and is marked with a pictogram of the full period of a sinusoid, Figure 1.
Pulsed (transformerless) power supplies are characterized by a pulsating current that increases from zero to a certain maximum value with a subsequent return to zero, without changing its sign. An RCD designed to detect such a mode is designated as A. The pictogram that marks them also contains the full period of the sinusoid as an indication of permanent change. current, the wave of which is supplemented from below by a meander, in a stylized form denoting a pulsating character current.
RCDs of type B are designed for protection against leakage current with a constant component and are mainly used in industry. Their pictogram is shown in Figure 3.
What RCD to use
The highest quality protection is naturally provided by RCDs, which were originally developed to protect against a specific type of leakage current.
In the realities of today, there is a great popularity of use in household low-current and electrical devices transformerless power supplies, as well as various thyristor regulators. The characteristics of such blocks are distinctly nonlinear. Taking this feature into account, other things being equal, it is advisable to dwell on type A RCDs. Moreover, in the operating instructions for some types of high-power household equipment (for example, washing machines and dishwashers), this provision is explicitly contained.
It is quite possible to dwell on cheaper AC type RCDs from leading manufacturers. It's connected with
- their good sensitivity to pulsating leakage currents;
- the likelihood of the occurrence of such currents is noticeably lower than with alternating ones.
RCDs of type B as devices demonstrate the widest functionality, however, their high cost is actually prohibitive for home use.