An RCD, residual current device, passes the line and neutral conductors through a toroidal core and trips when the imbalance, the residual current, exceeds its rating: commonly 30 mA for personal protection and 100 to 300 mA for fire protection. It detects current leaking to earth through damaged insulation or through a person, which fuses and breakers cannot see. Types AC, A, F and B respond to increasingly complex waveforms, up to the smooth DC leakage from inverters and EV chargers.
Press the test button on every RCD in the board, the one on the kitchen circuit didn't trip at all.
North Americans use GFCI for the 5 mA personnel device, Australians often say safety switch, and an RCBO is an RCD combined with an overcurrent breaker.
Also heard as
- RCCB
- GFCI
- safety switch
Related terms
Earth fault
Fault in which a live conductor makes unintended contact with earth or with earthed metalwork.
TT system
Earthing arrangement where the supply and the installation each have their own separate earth electrode.
Nuisance trip
Protective device opening with no real fault present, usually from bad settings, leakage or transients.