What are the three tripping curve types of RCBO?

Tripping Curve B - MCB with Trip Curve B trips instantly at a rate of three to five times its rated current. They are suitable for cable protection, residential and light commercial uses.

Tripping Curve C - MCB with Trip Curve C trips instantly at a rate of five to ten times its rated current. Typically used for high inductive loads. Suitable for domestic and residential applications.

Tripping Curve D - MCB with Trip Curve D trips instantly at a rate of ten to twenty times its current rate. Used for extremely high inductive loads such as motor with high inrush current.

How many types of RCD are there?

The International lEC Standard defines four types of RCD for AC applications. 

These types, which address the various kinds of residual current waveforms, are known as type AC, type A, type F (this paper does not explain) and type B. All these devices are intended to be used within AC supply systems.

Type AC residual current devices

Type AC RCD detect residual sinusoidal alternating currents. Type AC RCD are suitable for general use and cover most of the applications in practice.

Type A residual current devices

In addition to the detection characteristics of type AC RCD, Type A RCD detects pulsating DC residual current. Such waveforms can be caused by diode or thyristor rectifier circuit in electronic loads. Type A RCD are specifically intended to be used for single phase class 1 electronic loads.

Type B residual current devices

Type B RCD can detect sinusoidal AC, pulsating DC, composite of multi-frequency as well as smooth DC residual currents. In addition, tripping conditions are defined with different frequencies from 50Hz to 1kHz. In an AC electrical distribution network, a pure DC residual current can be mainly generated from three-phase rectifying circuits, but also from some specific single-phase rectifiers.

Type B RCD are intended to be used for loads with three-phase rectifier, such as variable speed drives, PV system, EV charging station and medical equipment.