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A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) [a] is an electrical safety device that interrupts an electrical circuit when the current passing through a conductor is not equal and opposite in both directions, therefore indicating leakage current to ground or current flowing to another powered conductor.
To eliminate this confusion, the IEC decided to apply the term residual current device (RCD) to differential-current-operated ELCBs. Residual current refers to any residue when comparing current in the outbound and return currents in the circuit. In a single phase circuit this is simply the live or phase current minus the neutral current.
GTO thyristors suffer from long switch-off times, whereby after the forward current falls, there is a long tail time where residual current continues to flow until all remaining charge from the device is taken away. This restricts the maximum switching frequency to about 1 kHz. It may be noted, however, that the turn-off time of a GTO is ...
When current flows from a line conductor to an earth wire, as is the case when a line conductor makes contact with an earthed surface in a Class I appliance, an automatic disconnection of supply (ADS) device such as a circuit breaker or a residual-current device (RCD) will automatically open the circuit to clear the fault.
Speed: Devices must function quickly to reduce equipment damage and fault duration, with only very precise intentional time delays. Sensitivity: Devices must detect even the smallest value of faults and respond. Economy: Devices must provide maximum protection at minimum cost. Simplicity: Devices must minimize protection circuitry and equipment.
To provide supplementary protection against high-impedance faults it is common to recommend a residual-current device (RCD) also known as a residual current circuit breaker (RCCB), ground fault circuit interrupter (GFCI), or residual current operated circuit-breaker with integral over-current protection (RCBO), which will cut off the supply of ...
A residual-current device (RCD), or residual-current circuit breaker (RCCB), is a device that instantly breaks an electric circuit to prevent serious harm from an ongoing electric shock. A fuse or circuit breaker also does that, 'instantly' of course, is subject to qualification.
Electrical equipment may be designed with a floating ground for one of several reasons. One is safety. For example, a low-voltage DC power supply, such as a mobile phone charger, is connected to the mains through a transformer of one type or another, and there is no direct electrical connection between the current return path on the low-voltage side and physical ground (earth).