Residual current operated circuit-breakers are amperometric protection devices which trip when the system leaks a significant current to earth.
They continuously calculate the vector sum of the single-phase or three-phase system line currents and, while the sum is equal to zero, they allow electricity to be supplied; supply is rapidly interrupted if the sum exceeds a value preset according to the sensitivity of the device.
Residual current operated circuit-breakers can be classed according to three parameters:
Besides, depending on the type of construction, residual current devices (RCDs) may be classed as RCBOs (magnetothermic with overcurrent protection), RCCBs (without overcurrent protection releaser incorporated) and RCD blocks.