Technology continues to evolve in the field of LV power distribution and protection. 30 years ago the specifier/installer was typically faced with the decision on what size fuse wire to use. Now they must consider which MCB or RCBO to install, with even more choice than ever on what levels of protection against the effects of electrical fault to afford. Due for release in the summer of 2018, BS 7671: Requirements for Electrical Installations (IET Wiring regulations) 18th edition will reference 4 potential types of protective device: In this particular article, we will look at the selection of MCBs and RCBOs and points to consider in this process. The decision to use Type B, C or D MCBs or RCBOs for final circuit protection in residential, commercial or industrial buildings can be based on a few simple rules. However, an understanding of the differences between these types of device can help the specifier or installer overcome problems of unwanted tripping, disconnections times for earth fault protection or issues associated with discrimination with upstream protective devices. The primary purpose of circuit protection devices such as MCBs is to protect the cable downstream of t...