A residual current device (RCD), similar to a Residual Current Circuit Breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor.

In the United States and Canada, a residual current device is also known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI). In Australia they are sometimes known as "safety switches" or simply "RCD" and in the United Kingdom they can be referred to as "trips" or "trip switches".

Working Principle

The RCCB works on the current balance principle. The supply conductors, i.e., the phases and the neutral, are passed through a torroid and form the primary windings of a current transformer. Its secondary winding is connected to a highly sensitive electromagnetic trip relay, which operates the trip mechanism.

In a healthy circuit, sum of the currents in phases, is equal to the current in the neutral and the vector sum of all currents is equal to zero. If there is any insulation fault in the current and leakage current flows to earth, the currents do not balance and their vector sum is not equal to zero. This imbalance is detected by the core balanced current transformer, the RCCB is tripped and supply to load is interrupted. The trip mechanism is operated at a residual current between 50-100% of its rated tripping current.

Technical information

Pole No.		2 Pole	4 Pole
Standard Conformity		IEC 61008-1	IEC 61008-1
Rated Current (In)	A	16, 25, 40, 63	16, 25, 40, 63
Sensitivity (I△n)	mA	30, 100, 300, 500	30, 100, 300, 500
Rated Voltage (Un)	Vac	240	240 / 415
Rated Insulation Voltage (Ui)	V	660	660
Rated Frequency	Hz	50	50
Type		A/AC	A/AC
Shortcircuit Withstand Capacity	kA	6	6
Residual Making Breaking Capacity	A	10 In	10 In
Ambient Temperature	oC	-25 to +40	-25 to +40
Shock Resistance	g	20	20
Vibration Resistance	g	3	3
Electrical Endurance/Mechanical	operations	10000	10000
Mounting		Din Rail (35 * 7.5) mm	Din Rail (35 * 7.5) mm
Degree of Protection		IP 20	IP 20
Terminal Capacity (max)	mm2	25	25

Dimension