5.8Specifying a residual current device#

When specifying the RCD, the following characteristics in Table 5 8(a) (with typical parameters) need to be considered and detailed for the particular application:

Table 5.8(a) – Typical residual current device characteristics

Characteristic	RCCB	RCBO
Type of installation	Fixed installation, mobile installation	Fixed installation, mobile installation
Rated voltage (Un)	240 / 415	240 / 415
Rated frequency (Hz)	50	50
Rated making and breaking capacity (kA)	3, 4.5, 6, 10	3, 4.5, 6, 10
Number of poles and current paths	Single pole RCCB with two current paths Two pole RCCB Three pole RCCB Three pole RCCB with four current paths Four pole RCCB	Single pole RCBO with one overcurrent protected pole and uninterrupted neutral Two pole RCBO with one overcurrent protected pole Two pole RCBO with two overcurrent protected poles Three pole RCBO with three overcurrent protected poles Three pole RCBO with three overcurrent protected poles and uninterrupted neutral Four pole RCBO with three overcurrent protected poles Four pole RCBO with four overcurrent protected poles
Rated current (A) (In)	6, 8, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125	6, 8, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125
Overcurrent protection	Without overcurrent protection	With overcurrent protection
Tripping characteristic		3In < B ≤ 5In 5In < C ≤ 10In 10In < D ≤ 20In
Rated residual operating current (mA)	6, 10, 30, 100, 300, 500	6, 10, 30, 100, 300, 500
Operating characteristic	AC, A	AC, A
Mounting method	DIN rail	DIN rail
Type of terminals	Screw type	Screw type

Notes

The residual current is the vector difference between phase and neutral currents. This will be 30 mA for personnel protection. The larger values are used for protection against fire and the lower values typically for hospital applications. The rated current is current carrying capacity of the device in normal operation and is the maximum demand load of the circuit or the rating of the overload protective device of the circuit. The rated making and breaking capacity of the device is the fault current that the contacts can close onto or open and break. This will depend on the available prospective short circuit current, typically of the order of 6 kA, and needs to be calculated at the point where the RCD is to be installed. RCDs must be suitably rated for the available fault current or be protected by a fuse or breaker. RCCBs require upstream protection. The possible waveform of a fault current to earth caused by various types of electronic equipment can affect the operation of RCDs and must be taken into account when selecting the type of RCD. Good quality RCDs have high immunity to nuisance tripping caused by high frequency and transient currents. Manufacturers’ data should be referred to when specifying RCDs to ensure the appropriate parameters are selected for the application.

The following (Table 5.8(b)) is a typical specification example of a single phase 16 A / 30 mA RCD with overcurrent protection:

Table 5.8(b) – Typical residual current device specification

Type of installation	Fixed
Rated voltage (Un)	240 V
Rated frequency	50 Hz
Rated short-circuit capacity Icn	6 kA
Number of poles and current paths	Single pole
Overcurrent protection	RCBO
Rated current (In)	16 A
Tripping characteristic (RCBO)	Type C
Rated residual operating current (IΔn)	30 mA
Operating characteristics	Class AC
Degree of protection (IP)	Unenclosed
Method of mounting	Switchboard, DIN rail
Type of terminals	Screw-type