new consumer units contain fuses or MCBs (miniature circuit breakers) that only provide overcurrent and
short circuit protection but have no earth fault protection; this would be provided by the installation of an 'RCD' (residual current device). In 1997 the Department of Trade and Industry published a report stating that their research suggested that 20% of electrical fires would be prevented by the use of RCDs in fuseboards. The Electrical Safety First's statistics from 2010 indicate that still roughly one third of all homes in the UK have electrical installations without RCD protection.
The most common
way of providing RCD protection is to install a new fuseboard or
'consumer unit' that includes one or more RCDs protecting the circuits
fed by the fuseboard. Often the RCDs will provide earth fault
protection for up to
5 circuits. While this is safe, when earth fault
conditions occur the RCD will trip and power will be lost to all those
This can cause a lot of inconvenience, especially if a fridge or freezer
connected to one of the circuits, as any food inside the appliance could
spoiled. We fit fuseboards containing 'RCBO's. An 'RCBO' is a combined
RCD and MCB and will provide overcurrent, short circuit and earth fault
protection all in one switch. As each circuit will have a dedicated
RCBO, 'nuisance tripping' of other circuits doesn't occur and the
freezer doesn't defrost if other appliances in the home trip the RCD.