Type B RCD, B Type RCCB & Type B RCBO

What are RCDs?
RCDs is a generic term and it is commonly used to refer to devices such as RCCBs, RCBOs and other types of earth leakage detection operated protective devices.

What does the regulations say?
The use of RCDs particularly 30mA devices has been extended to include more applications and more types of installation in consecutive additions of the wiring regulations. For example 18th Edition requires all luminaire circuits in domestic household premises to be protected by 30mA RCD .
Consequently, greater emphasis is placed on protection against unwanted tripping of RCDs (see 531.3.2) and correct selection of the right type of RCD for each application. For example, in medical locations group 1 and 2, Type A or B are required.

What are my options?
Differing types of RCD are available; this section related to the various types.

For example reference is made to Type AC RCDs which are for general use.

Reference is also made to Type A, Type F & Type B RCDs which also detect pulsating DC residual current.

The appropriate type of RCD should be selected for each application, see 531.3.3.

Type AC RCD– General purpose use
Type A RCD– Where smooth DC to 6mA exists
Type F RCD– Where smooth DC to 10mA exists
Type B RCD– Where smooth DC to 0.4 times rated operating current, or 10mA, whichever is higher
This section is expanded considerably to aid designers with the selection of appropriate devices for particular applications.

EV Type A or B RCD may be required and in Section 712 Solar photovoltaic (PV) power supply systems, Type B RCD may be required.

How do I choose the right RCD?
The term RCD is used over 250 times in the 18th Edition of the Wiring Regulations.

To ensure that the correct type of RCD is selected the designer must match the operating characteristic of the RCD to the type of fault that can occur in the installation/equipment and manufacturer instructions should be consulted in the design and selection process.

What you need to know about RCDs and the 18th Edition
People talking about RCDs and the 18th Edition is, most of the time, a good thing, but occasionally it’s a dangerous thing.