COMMON CONSUMER UNIT DEVICES AND CONFIGURATIONS
MAIN SWITCH
RCD
MCB
RCBO
AFDD/RCBO
MAIN SWITCH:
The main switch isolates the incoming supply to the whole consumer unit. This can only be operated manually.
RCD (Residual Current Device):
An RCD is a device designed to provide protection against electrocution or electrical fires, by isolating all the circuits protected by that device when it detects an earth leakage fault.
Often an RCD will protect a number of circuits within the consumer unit. In some older installations it can be used as a main switch which means the RCD protects the entire installation.
For more information regarding RCD protection, please click here.
MCB (Miniature Circuit Breaker)
An MCB device operates upon detection of a short circuit fault or overload. An installation will be divided into individual circuits, with a suitably sized circuit breaker protecting it.
RCBO (Residual Current Circuit Breaker with Overload Protection)
An RCBO device incorporates the functions of an RCD and an MCB, meaning they will operate upon detection of an earth leakage fault, short circuit fault or overload.
RCBOs protect individual circuits, meaning that in the event of a fault, only the affected circuit will be isolated and the rest of the installation will remain energised.
AFDD/RCBO (Arc Fault Detection Device/ Residual Current Circuit Breaker with Overload Protection)
An AFDD/RCBO device incorporates the functions of an AFDD, an RCD and an MCB, meaning they will operate upon detection of an arc fault, an earth leakage fault, short circuit fault or overload.
AFDD/RCBOs protect individual circuits, meaning that in the event of a fault, only the affected circuit will be isolated and the rest of the installation will remain energised.
Main Switch and RCBOs:
Each individual circuit within the installation is protected by an RCBO device.
In the event of a fault, only the affected circuit will be isolated. The rest of the installation will remain energised, thereby minimising inconvenience and danger.
Although this configuration is more expensive than the options below, it offers the best protection, whilst minimising danger and inconvenience. Therefore it is our preferred option when installing a new/replacement consumer unit.
Split load with main switch and dual RCD:
The consumer unit is divided into two sections. Each section comprises of a number of MCBs, protected by an RCD.
In the event of a fault and the RCD tripping, the associated circuits will be isolated.
The other section of the consumer unit, protected by the other RCD, will remain energised.
High integrity with main switch and dual RCD:
This is similar to a split load consumer unit with dual RCD, however it facilitates the addition of MCBs without RCD protection, or individual RCBO devices.
Whilst RCD protection is necessary on most circuits in a domestic property, there are certain exceptions where the omission of an RCD is permitted/required, and therefore this configuration can be advantageous over a basic dual RCD arrangement.
Split load with main switch and single RCD:
The consumer unit is divided into two sections. One section comprises of a number of MCBs without RCD protection. The other section comprises of MCBs protected by an RCD.
In the event of a fault and the RCD tripping, the associated circuits will be isolated. The circuits on the other side of the consumer unit, protected by just MCBs will remain energised.
Although this configuration may be found in older installations, it is no longer compliant with BS7671 IET Wiring Standards.
