3. RCD - effective fire and electrical protective means

3.1. GENERAL PROVISIONS

The residual current protective devices reacting to the differential current, along with the overcurrent protection devices, relate to additional types of protection of the person from injury during indirect contact provided by automatic power-off. Overcurrent protection (when using protective zero-pointing) provides protection of the person with an indirect touch - by switching off the circuit breakers or fuses of the damaged section of the circuit with a short circuit to the housing.

At low short-circuit currents, lowering the insulation level, and also when the protective conductor is cut off, zeroing is not effective enough, so in these cases the RCD is the only means of protecting a person from electro-destruction.

At the heart of the protective shutdown, as an electro-protective device, is the principle of limiting (due to rapid disconnection) the duration of the current flowing through the human body when it is unintentionally touched by the elements of the electrical installation under voltage (Figure 3.1). Of all known electrical protective devices, the RCD is the only one that provides protection of a person from electric shock by direct contact with one of the current-carrying parts.

Fig. 3.1. Graph of areas of physiological effect on human AC (50-60 Hz) according to IEC 479-94, Ch. 2,3 and the time-current characteristics of the RCD:

1 - imperceptible currents; 2 - tangible, but not causing physiological abnormalities; 3 - palpable, but not risking cardiac fibrillation; 4 - palpable, risky heart fibrillation (probability <5%); 5 - palpable, risking heart fibrillation (probability <50%); 6 - palpable, risky heart fibrillation (probability> 50%); A and B are the time characteristics of the RCD (I _{D n} = 10mA and I _{D n} = 30mA)

Another, no less important property of the RCD is its ability to protect against fires and fires occurring at sites due to possible insulation damage, electrical wiring faults and electrical equipment.

According to the VNIIPO of the Ministry of the Interior of Russia, more than a third of all fires occur due to the ignition of electrical wiring as a result of heating the conductors along the entire length, sparking, burning of an electric arc on any element caused by short-circuit currents.

Short circuits, as a rule, develop from insulation faults, earth faults, leakage of current to ground. RCD, reacting to the leakage current to the ground or protective conductor, in advance, before development in a short circuit, disconnects the electrical installation from the power source, thus preventing unacceptable heating of the conductors, sparking, arcing and possible subsequent ignition.

In some cases, the energy released at the location of the insulation damage in the course of leakage currents is sufficient for the occurrence of a fire and, as a consequence, a fire. According to various domestic and foreign sources, the local ignition of insulation can be caused by a rather small capacity, allocated at the point of leakage. Depending on the material and the service life of the insulation, this power is only 40-60 W. This means that the timely operation of a fire protection RCD with a set value of 300 mA will prevent the allocation of the specified power, and, therefore, will not allow a fire.

The first protective shutdown device was patented by the German company RWE (Rheinisch-Westfalisches Elektrizitatswerk AG) in 1928 (DRP No. 552 678 of 08.04.28). For the first time, the principle of current differential protection, previously used to protect generators, lines and transformers, was used to protect a person from electric shock.

In 1937, the firm Schutzapparategesellschaft Paris & Co. Manufactured the first acting device based on a differential transformer and a polarized relay, which had a sensitivity of 0.01 A and a speed of 0.1 s. In the same year, with the help of a volunteer-employee of the firm, an RCD test was conducted. The experiment ended well, the device worked clearly, the volunteer experienced only a slight electric shock, although he refused to participate in further experiments.

All the following years, with the exception of the military and the first post-war years, intensive work was carried out to study the effect of electric current on the human body, the development of electrical protective means and, first and foremost, to improving and introducing RCD.

In the 70s, in our country, research, experimental and experimental design work was actively carried out to create and implement a wide-range RCD. At several enterprises, the production of RCD was mastered, unfortunately, in small volumes. Of great importance was the equipment of a number of schools in the country, which was carried out in the 1980s, by means of UZOSH (school). This device is still produced by the Gomel Plant "Electroapparatura". This plant also produces ZOOP-25 devices (for agricultural electrical equipment), UZO-B (the device was originally designed as a UZO-plug for connecting washing machines).

When the hotel "Russia" was reconstructed after the infamous fire, all hotel rooms were equipped with domestic RCDs, manufactured by special order by one of the defense enterprises.

In the 1960-70's. In the whole world, first of all in the countries of Western Europe, Japan, the USA active introduction of RCDs into wide practice began.

Currently, hundreds of millions of RCDs successfully, as evidenced by official statistics, protect the lives and property of citizens of France, Germany, Austria, Australia and other countries from electro-fires and fires.

RCD has long become a familiar and mandatory element of any electrical installation of industrial or social purpose.

RCD is an indispensable element of any switchboard, these devices are equipped with all necessary mobile devices (residential houses-trailers at camping sites, vans, public catering vans, small temporary electrical installations of outdoor installation, for example, arranged on the areas for festive festivities), Hangars, garages.

RCDs are built into socket outlets or plugs, through which power tools or household electrical appliances operated in especially dangerous - wet, dusty, conductive floors, etc., are connected. Premises.

Insurance companies in assessing the risk that determines the insured amount, necessarily take into account the presence of an RCD insurance facility and their technical condition.

Currently, each resident of these countries accounts for an average of two RCDs. Nevertheless, dozens of companies for many years are stable, in significant quantities they produce these devices of various modifications, constantly improving their technical parameters.

It should be noted that the term "protective trip device - RCD", adopted in the domestic specialized literature, most accurately determines the purpose of this device and its difference from other switching electrical devices - circuit breakers, load switches, magnetic starters, etc.

Abroad adopted the following designations:

• In Germany, Austria - Fehlerstrom-Schutzschalter (Fehlerstrom-Schutzeinrichtung). Short: FI-Schutzschalter (F-Fehler - fault, malfunction, leak, I - current symbol in electrical engineering, Schutzschalter - safety switch, Schutzeinrichtung - protective device);
• In France - DD - disjoncteur differentiel (differential switch);
• In the UK, elcb (earth leakage circuit breaker);
• In the USA, GFCI (Ground Fault Circuit Interrupter).

Table 3.1.

RCD	Residual current protective device - protective device for differential (difference) current (common name of RCD)
PRCD	Portable residual current protective device
PRCD-S	Portable residual current protective device-safety - portable protective device for differential current (in the cable extension)
SRCD	Fixed socket outless residual current protective device - protective device for differential current (built into the socket)
RCCB	Circuit-breakers without integral overcurrent protection - a differential current protective device without built-in overcurrent protection
RCBO	Over current protection circuit breaker with integrated overcurrent protection with built-in overcurrent protection
RCM	Residual current monitor - differential current monitoring device (leakage current)

Currently, the international classification of RCD, developed by the International Electrotechnical Commission (IEC) - is in effect (Table 3.1).

Common name - RCD - residual current protective device.

The exact translation is a protective device based on the difference (differential) current.

Note.

Very often, even in standards, there is a translation of the word "residual" as "residual", which causes various misunderstandings, because in the domestic electrotechnical terminology there is no term "residual current".

Another inaccuracy, also embedded in the standards, is the definition of RCD as a "residual current controlled device". Here, an elementary causal relationship is broken. The device is not controlled by this current, but reacts to it!

In the latest domestic standards (GOST R 51326, 51327), the terminology has also been violated: unlike the definition adopted in the main standard (GOST R 50807-95), the RCD is called the differential current switch - VDT, then the automatic residual current circuit breaker - RCBT, which Experts mislead.

Often, another, non-conforming name of the RCD - "differential switch", is used. This name has spread from non-specialist electricians translated prospectuses of foreign firms and refers to "RCD with built-in protection against overcurrents."