What is a split-load consumer unit?

A split-load consumer unit has your circuits divided into two sections, separated by two RCDs. One section covers circuits that need RCD protection (sockets, bathroom, outdoor). The other section covers circuits that don't need it or shouldn't be interrupted unexpectedly (smoke alarms, freezers, alarm systems). This design was common in the 2000s and early 2010s. The problem is that if one circuit in the protected group develops a fault, the whole group's RCD trips — cutting power to all protected circuits at once. This can be disruptive. The modern preferred alternative is a full RCBO board, where each circuit has its own individual protection, so only the faulty circuit trips. If you have a split-load board and find that one fault takes out many circuits at once, your electrician may recommend upgrading to a full RCBO board for better protection and convenience.