Upon their tripping sensitivity (IΔn value), RCDs are classed as:
▪ low-sensitivity (IΔn > 0.03 A) RCDs, not suitable for protection against direct contacts; coordinated with the earth system according to the formula IΔn < 50/R, to provide protection against indirect contacts;
▪ high-sensitivity (IΔn: 0.01 … 0.03 A) or “physiologically sensitivity” RCDs for protection against indirect contacts, with simultaneous additional protection against direct contacts.
Upon their tripping time, RCDs are classed as:
▪ instantaneous or rapid or general RCDs
▪ type S selective or, not correctly, delayed RCDs.
Selective RCDs (RCBOs, RCCBs or RCD-blocks) have a delayed tripping action and are installed upstream of other rapid residual current operated circuit-breakers to guarantee selectivity and to limit the power out only to the portion of the system affected by a fault.
The tripping time is not adjustable: i is set according to a predetermined time – current characteristic with an intrinsic delay for small currents, tending to disappear as the current grows.
IEC/EN 61008 and 61009 establish the tripping times relative to the type of RCD and the IΔn.
The range of ABB RCDs also includes AP-R (anti-disturbance) devices which trip according to the limit times allowed by the Standards for instantaneous RCDs. This function is due to the slight tripping delay (approx. 10 ms) relative to the standard instantaneous ones.