Residual current device serves for protection against electric shock, emergency shutdown network when leakage occurs.
Many believe that these objectives handle breakers, but it is not.
Why do I need RCD
Over time, the insulation of the wiring and electrical appliances aging. When the closure wire for ungrounded housing device there is a danger of electric shock of impact. When you touch the wire to the walls according to the latest leak current flows that may cause a fire.
Circuit breakers are triggered by short circuit and overload, when currents flow through them, measured in amperes. For man poses a risk of leakage current exceeding 10 mA, which is hundreds of times smaller than current automatic switching. Fire can occur if the leakage currents of 0.3 A. On the other hand RCD is not activated during short circuits, therefore, can not replace machines. Security features of leaks and short circuits are combined in differential machines.
Circuit breakers are selected according to the rated current, the RCD - sensitivity, measured in milliamps. circuit breakers which serve to protect humans, disable voltage when leakage currents up to 30 mA, for fire protection of - 100 to 300 mA.
The device, a principle of action, classification
RCD formed in the dielectric housing. On the case are:
- release lever;
- button to perform the tests;
- input and output terminals;
- marking (manufacturer logo, rated voltage and current connection circuit, the leakage current).
The apparatus includes a differential transformer, trip coil, trip unit, for testing circuit. If there is no leakage of the windings of the transformer load current flows only (see. figure below).
Since winding included counter and on them the same current flows, magnetic flux induced in the transformer core, are mutually compensated.
When the leakage currents in the windings are different, so that the magnetic fluxes are not compensated. current occurs in the control circuit acts on the trip coil. The release is triggered and breaks the circuit. To verify that the device is used "Test" button, the closing phase to ground through resistance.
By the nature of the leak and the character of the RCD tripping current is divided into the following types:
- AU - instantaneous operation, a sinusoidal current;
- A - instantaneous operation, direct or alternating current;
- B - instant activation, pulsating, variable, constant currents;
- S, G - operation with a time delay.
There RCD mechanical and electronic action. Electronic devices do not work in case of interruption of the neutral conductor to an electrical shield, however considered to be less reliable.