Within domestic installations there are numerous regulations within BS 7671:2018 concerning additional protection through the use of 30mA RCDs…
411.3.3: Gives us additional protection via a 30 mA RCD for ‘general’ sockets, both indoor and outdoors.
411.3.4: Again 30 mA RCD additional protection for all lighting circuits.
522.6.202: Cables buried in a wall less than 50mm from the surface that are run in the prescribed cable zones see 522.6.202 (i) but are not mechanically protected by any of the methods within 522.6.204 (i) to (iv) or are extra-low voltage 522.6.204 (vi) shall be provided with additional protection as in 415.1.1 ’30mA RCD’.
701.411.3.3. Any circuits serving a room containing a bath or shower (ie lights and shower etc) and any circuits that pass through zones 1 or 2 shall have one or more 30mA RCDs providing additional protection. There is no requirement to put showers on their own RCD such as a 45A / 30mA RCBO and they can be grouped with the rest of the circuits and provided with additional protected with a 30mA RCCB, but it may be considered as a good practice to do so.
These regulations ensure that all circuits within a domestic installation should be provided with additional protection via a 30 mA RCD which can either be through the use of RCCBs which provide additional protection to multiple circuits, with overload protection provided by the individual circuit breakers. Or by the use of RCBOs which will provide individual ‘RCD and overload’ circuit protection.
NOTE: 30mA RCD’s are used for additional protection because potentially any fault current of 50mA (0.05A) or more can be fatal. So 30mA RCDs are there to provide additional protection for people and not the installation, and domestic installations are full of unskilled and unsupervised people who are unaware of the potential dangers of electricity and need to provided with additional protection.