Residual current device RCD.
At the moment, RCDs are successfully installed in newly driven electrical installations. But the installation and application of RCDs and at the moment raises questions for both subscribers and employees involved in the installation of electrical installations.
So what is an RCD?
Residual current circuit breakers (RCDs) that respond to differential current, along with overcurrent protection devices, are additional types of protection against damage to a person by indirect contact provided by automatic power off.
In contrast to overcurrent protection devices, RCD is the only means of protecting a person from electric shock at low fault currents, lowering the insulation level, and is not effective enough. Overcurrent protection (when using protective grounding) protects a person when touched indirectly - by switching off the damaged part of the circuit with a short circuit to the casing by circuit breakers or fuses. Of all the known electrical protective equipment, an RCD is the only one that provides protection for a person from electric shock when directly touching one of the live parts. Also, RCDs are excellent protection against possible insulation damage, electrical wiring and electrical equipment malfunctions, which are 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 RCD was carried out. In 1960-1970. all over the world, primarily in the countries of Western Europe, Japan, the USA, the active introduction of RCDs into widespread practice has begun. 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 electric shock and fires.
The principle of operation of the RCD.
UZO is a high-speed protective device that responds to differential current in conductors that transmit electricity to the protected electrical installation. The RCD action is based on the operation of a differential current transformer. The total magnetic flux in the core - Ф, is proportional to the difference in currents in the conductors, which are the primary windings of the current transformer, IL and IN, induces an emf in the secondary winding of the transformer, under the influence of which current I flows in the secondary winding circuit proportional to the difference of the primary currents. This current drives the trigger. In 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 to the body of an electrical receiver, on which an insulation breakdown has occurred, along with the phase conductor, an additional current flows in addition to the load current through the RCD - the leakage current, which is a differential (differential) current transformer. The inequality of currents in the primary windings causes an imbalance of magnetic fluxes and, as a result, the appearance of a transformed differential current in the secondary winding. If this current exceeds the setting value of the threshold element of the trigger, the latter is triggered and acts on the actuator. To monitor the serviceability (operability) of the RCD, a test circuit is provided (the "Test" button), which works by artificially creating a disconnecting differential current.
The main errors in the installation of RCDs.
The most common mistake in the installation of RCDs is the connection to the RCD of the load, in the circuit of which there is a connection of the neutral working conductor N with open conductive parts of the electrical installation or a connection with the neutral protective conductor PE. In this case, the likelihood of "arbitrary" operation of the RCD is very high. The following errors are also possible: connecting loads to the neutral conductor to the RCD, connecting the loads to the neutral working conductor of another RCD, a jumper between the neutral working conductors of various RCDs, connecting the PE and N conductors on the load side.
An example of the inclusion of RCDs.
Regulatory regulatory documents.
- Electrical Installation Rules Ed. 7th
- GOST 12.4.155-85. "Residual current devices. 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 showers."
- GOST R 50571.15-97 (IEC 364-5-52-93). Part 5. "Selection and installation of electrical equipment. Chapter 52. Wiring."
- GOST R 50 669-94. "Power supply and electrical safety of mobile (inventory) buildings made of metal or with a metal frame for street trading and consumer services. Technical requirements."