RCD/ELCB and sensibility
Legal text :
Standard IEC 60755 (General requirements for residual current operated protective devices) defines three types of RCD depending on the characteristics of the fault current.
Definition : Type AC: RCD for which tripping is ensured
for residual sinusoidal alternating currents
Definition : Type A: RCD for which tripping is ensured
as for type AC
for residual pulsating direct currents
for residual pulsating direct currents superimposed by a smooth direct current of 6 mA, with or without phase-angle control, independent of the polarity
Definition : Type B: RCD for which tripping is ensured
as for type A
for residual sinusoidal currents up to 1 kHz
for residual sinusoidal currents superposed by a pure direct current
for pulsating direct currents superposed by a pure direct current
for residual currents which may result from rectifying circuits
- three pulse star connection or six pulse bridge connection
- two pulse bridge connection line-to-line with or without phase-angle monitoring, independently of the polarity
Immunity level of Schneider Electric RCDs
Sensibility and rated current
RCD sensitivity is expressed as the rated residual operating current, noted IΔn. Preferred values have been defined by the IEC, thus making it possible to divide RCDs into three groups according to their IΔn value
High sensitivity (HS): 6 – 10 – 30 mA (for direct-contact / life injury protection)
Medium sensitivity (MS): 100 – 300 – 500 – 1,000 mA (for fire protection)
Low sensitivity (LS): 3 – 10 – 30 A (typically for protection of machine)
Due to its design a RCD/ELCB does not guaranty to open the circuit at the exact value of the sensibility. By standards, it has been defined that a RCD/ELCB will trig for a 
4.3. Delay
Definition :
A RCD/ELCB will trig and open the circuit in the time defined by the manufacturer. This time depends on the type: instantaneous, selective and delayed. The trigger time is composed of the time of detection and the time of operating. A delay can be added. (IEC / EN 61008 (RCD) or IEC / EN 61009 (RCCD)
Instantaneous
Selective
The no response time is a delay to allow the above RCCD to trig.
