Device for residual current protection.
At present, the RCD is successfully installed in newly installed electrical installations. But the installation and use of RCDs and to the present time raises questions, both for subscribers and for workers engaged in the installation of electrical installations.
So what is an RCD?
The residual current protective devices (RCDs) reacting to the differential current, along with the overcurrent protection devices, relate to additional types of protection of the person from injury with indirect contact provided by automatic power-off.
Unlike the means of protection from overcurrent, the RCD is the only means of protecting a person against electric shock at low short-circuit currents, reducing the insulation level, is not effective enough. Overcurrent protection (when using protective zeroing) provides protection of a person with an indirect touch - by disconnecting the circuit breakers or fuses of the damaged section of the circuit with a short circuit to the housing. Of all the 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. Also, the RCD is an excellent protection against possible insulation damage, electrical wiring faults and electrical equipment considered to be the main cause of fires and fires occurring in electrical installations.
A bit of history.
For the first time in 1937 the company 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, a full-scale test of the RCD was carried out. In the 1960-1970'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.
Principle of operation of the RCD.
RCD is a high-speed protection device that reacts to a differential current in conductors that pass electricity to the protected electrical installation. The operation of the RCD is based on the operation of the differential current transformer. The total magnetic flux in the core is Φ, proportional to the difference in the currents in the conductors, which are the primary windings of the current transformer, IL and IN, in the secondary winding of the transformer, emf, which causes the secondary current to flow in the secondary circuit , proportional to the difference of primary currents. This current drives the trigger. In the normal operating mode, the resulting magnetic flux is zero, the current in the secondary of the differential transformer is also zero. When a person touches open conductive parts or the housing of an electrical receiver that has been subjected to an insulation breakdown, an additional current flows through the phase conductor through the RCD, in addition to the load current, which is a differential current for the current transformer. Inequality of currents in primary windings causes unbalance of magnetic fluxes and, as a consequence, the appearance of a transformed differential current in the secondary winding. If this current exceeds the threshold value of the threshold element of the trigger, the latter operates and acts on the actuator. To monitor the serviceability of the RCD, a testing circuit is provided (the "Test" button), which works by artificially creating a tripping differential current.
Basic errors in the installation of RCDs.
The most common error in the installation of a RCD is the connection to the RCD of a load in the circuit of which there is a connection of the zero working conductor N with open conductive parts of the electrical installation or connection to the zero protective conductor PE. In this case, the probability of an "arbitrary" tripping of the RCD is very high. The following errors are also possible: connection of loads to the neutral conductor to the RCD, connection of loads to the neutral conductor of the other RCD, jumper between the neutral conductors of various RCDs, connection on the load side of the PE and N conductors in the socket.
Example of switching on RCD.
Regulatory regulatory documents.
- Rules for the installation of electrical installations. 7th.
- GOST 12.4.155-85. "Residual current circuit breakers - Classification - General requirements"
- GOST R 50807-95 (IEC 755-83). "Devices protective, controlled by differential (residual) current"
- GOST R 50571.3-94 (IEC 364-4-41-92). "Electrical installations of buildings - Safety requirements - Protection from electric shock".
- GOST R 50571.11-96 (IEC 364-7-701-84). "Electrical installations of buildings - Part 7. Requirements for special electrical installations - Section 701. Bathrooms and showers".
- GOST R 50571.15-97 (IEC 364-5-52-93). Part 5. "Selection and installation of electrical equipment." Chapter 52. Electrical wiring. "
- GOST R 50 669-94. "Electrical supply and electrical safety of mobile (inventory) buildings of metal or with a metal frame for street trade and consumer services." Technical requirements. "
And others …