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:
Detectable wave form
Tripping sensitivity and tripping time
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
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