A standard split-load consumer unit divides circuits between two groups, each protected by a shared RCD (residual current device). While this arrangement meets the requirements of many installations, it has a practical drawback: if the RCD trips—perhaps because of a fault on a washing machine or an outdoor socket—it disconnects every circuit on that half of the board at once.
This can mean losing lighting, heating control, and refrigeration simultaneously. An RCBO (residual current breaker with overcurrent protection) combines the overcurrent protection of an MCB with individual earth leakage detection.
When an RCBO is fitted to each circuit, a fault on one circuit trips only that circuit, leaving every other circuit unaffected. This arrangement is known as full RCBO protection.
Upgrading to an RCBO consumer unit is carried out by replacing the existing unit with one that accepts individual RCBOs. The electrician will isolate the board from the supply, verify the condition of the existing circuit wiring, and reconnect each circuit to its own RCBO of the correct current capacity.
The work must be notified to building control and a completion certificate issued. RCBO protection is particularly useful in properties where loss of lighting on a staircase, loss of a refrigeration circuit, or loss of power to a medical device would present a practical or safety concern.
It also simplifies fault-finding, because a tripped circuit immediately indicates which part of the installation is affected.