Question 3 of 4 in our series on protective devices - What are Bidirectional and a Unidirectional protective devices?
BEAMA issued a technical bulletin in 2024 detailing a concern where certain protective devices failed to safely operate when required where current flowed in either direction.
An electrical installation having more than one source of supply current may create the conditions where current can flow in more than one direction. Where this is the case, it is necessary that protective devices are able to operate correctly in whichever direction current flows.
To address the issue of current flowing in two directions Amendment 3 of BS 7671 (BS 7671: 2018+A3:2024) was issued on 31st July 2024. The amendment introduced one new requirement (Regulation 530.3.201) and two new definitions.
• Bidirectional protective device – A protective device where it is intended by the manufacturer that a source of supply is connected to either or both sets of connection terminals.
• Unidirectional protective device - A protective device where it is intended by the manufacturer that a source of supply is only connected to one defined set of connection terminals.
Direction of connection
Single-pole, single-pole and neutral (two-pole) and double-pole devices are typically labelled with ‘In’ or ‘Supply’ and ‘Out’ or ‘Load’.
Where devices are labelled ‘In/Out’ or ‘Supply/Load’ they will always be unidirectional in nature, and under certain conditions should not be selected for use. Unidirectional devices can always be used where there are no alternative sources of supply. Bidirectional devices will not be specifically labelled with in and out and are likely to be labelled with ‘L/N’ or ‘L1/N1’ and ‘L2/N2’. Bidirectional devices are likely to be necessary where multiple sources of supply exist.
With the increasing installation of prosuming electrical installations it will be necessary for designers and installers to utilise bidirectional protective devices.
To find out more about RCBOs and other protective devices go to https://www.youtube.com/watch?v=Hn9Mz7v58pg where Jake Green and Tim Benstead discuss how protective devices have evolved over the years.