Device of protective shutdown of UZO.
At present, the RCD is successfully installed in newly installed electrical installations. But the installation and use of RCDs and currently raises questions, both among subscribers and the workers involved in the installation of electrical installations.
So what is RCD?
Residual current devices (RCDs) reacting to the differential current, along with overcurrent protection devices, are additional types of protection for a person from damage by indirect contact, provided by automatic power off.
In contrast to the means of protection against overcurrent, the RCD is the only means of protecting a person against electric fire at low circuit currents, reducing the insulation level, is not effective enough. Protection against overcurrent (when using protective zeroing) provides protection for a person in case of indirect contact - by switching off the damaged part of the circuit with an automatic switch or fuses during a short circuit to the case. Of all the known electrical protective devices, the RCD is the only one that protects a person from electric shock by direct contact with one of the live parts. Also, RCD is an excellent protection against possible damage to the insulation, electrical wiring faults and electrical equipment considered the main cause of fires and fires that occur in electrical installations.
A bit of history.
For the first time in 1937, Schutzapparategesellschaft Paris & Co. manufactured the first operating 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 - an employee of the company, a full-scale test of an RCD was conducted. In 1960-1970 throughout the world, primarily in the countries of Western Europe, Japan, and the United States, the active introduction of UZOs into widespread practice began. Currently, hundreds of millions of USTs successfully, as evidenced by official statistics, protect the lives and property of citizens of France, Germany, Austria, Australia and other countries from electrical damage and fires.
The principle of operation of the RCD.
RCD is a high-speed protective agent that reacts to the differential current in conductors that transmit electricity to the protected electrical installation. The action of the RCD is based on the operation of a differential current transformer. The total magnetic flux in the core - F is proportional to the difference of currents in the conductors, which are the primary windings of the current transformer, IL and IN, induces in the secondary winding of an electromotive energy transformer under the action of which a current I flows proportional to the difference in primary currents. This current activates the trigger mechanism. In normal operation, the resulting magnetic flux is zero, the current in the secondary winding of the differential transformer is also zero. When a person touches open conductive parts or to the case of an electrical receiver, on which an insulation breakdown occurred, an additional current flows through the phase conductor through the RCD, which is a differential current (differential) for the current transformer. The inequality of currents in the primary windings causes an imbalance of magnetic fluxes and, as a consequence, the appearance of a transformed differential current in the secondary winding. If this current exceeds the setting value of the threshold element of the starting organ, the latter is triggered and acts on the actuator. To monitor the health (operability) of the RCD, a testing circuit is provided (the “Test” button), which works by creating an artificially disconnecting differential current.
The main errors in the installation of the RCD.
The most common mistake when installing an RCD is to connect a load to the RCD, the circuit of which has a connection of the neutral working conductor N with the exposed conductive parts of the electrical installation or a connection with the neutral protective conductor PE. In this case, the probability of an “arbitrary” operation of the RCD is very high. The following errors are also possible: connecting loads to a neutral conductor up to the RCD, connecting loads to the zero working conductor of another RCD, a jumper between the zero operating conductors of different RCDs, the connection on the load side of PE and N conductors in the socket.
An example of the inclusion of the RCD.
Regulatory regulatory documents.
- Rules for electrical installations. Ed. 7th
- GOST 12.4.155-85. "Devices of protective shutdown. Classification. General requirements"
- GOST R 50807-95 (IEC 755-83). "Protective devices controlled by differential (residual) current"
- GOST R 50571.3-94 (IEC 364-4-41-92). "Electrical installations of buildings. Safety requirements. Protection against 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 shower rooms."
- 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. "Power supply and electrical safety of mobile (inventory) buildings from metal or with a metal frame for street trading and consumer services of the population. Technical requirements."