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What is Residual Current Device (RCD)

  •  What is Residual Current Device  (RCD), rcd, Residual Current Device, current of 30mA,



    Residual-current device is protective and life-saving device. It is designed to protect from an electric shock, if you touch phase live conductor a current of 30 milli amperes can be lethal for a person, if it persists for more than a fraction of second. In most scenario installation is protected only by fuse or MCB miniature circuit breaker fuse protects from overload or short-circuit but does not protect from electrical shock human body have very high resistance so if somebody accidentally touch live conductor very small current will flow trough body about 30 milli amperes that is not enough to trigger fuse but is lethal for a person. The basic principle that uses RCD is that current in the phase conductor and neutral conductor must be the same, if there is difference the current must be leaking somewhere perhaps through a person and neutral conductor. Also known as earth leakage circuit-breakers (ELCBs). These are devices which interrupt the present during a circuit whenever a predetermined level of current (usually 30mA) to earth is detected. Their purpose is to help prevent electrocution accidents for the cases when the current flows through the body to the general ground mass earth.


    What is Residual Current Device (RCD), rcd, Residual Current Device, current of 30mA,



    Under healthy conditions the currents within the conductors passing through the toroidal transformer are balanced, there's no flux induced within the core and no voltage induced within the secondary coil of the transformer.


    Should some current flow to earth through a fault and thus return to the availability transformer without returning through the acceptable primary of the core-balance device, then the resultant of the currents through the primaries will be equal to the earth fault current. A magnetic flux will

    then be generated in the toroidal core and a voltage induced in the transformer secondary. This voltage is employed to trip the breaker .


    In order to reach protection state, the RCDs which have a 30mA current ampere and they trip in 0.3s are needed for:

    for sockets and lighting system circuits is applicable
    sockets and outlet in residential area for the installation of equipment in wet area

    Note there are certain situations where RCD is not used as it can cause nuisance tripping, e.g. stoves, water heaters.




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