What the consumer unit does
Every circuit in your home starts at the consumer unit. It contains the main switch that isolates the house, and protective devices that disconnect a circuit when something goes wrong. Circuit breakers respond to overloads and short circuits. RCDs respond to current leaking to earth, which is what happens when someone touches something live, and they disconnect in a fraction of a second.
Older fuse boxes have fuses that deal with overloads but offer no protection against electric shock. That difference is the main reason replacement is worthwhile.
Signs yours is due
Rewireable fuses, where a length of fuse wire sits in a ceramic carrier.
A wooden back board or a plastic enclosure. Current regulations require consumer units in homes to be made of non-combustible material, usually steel.
No RCD, or a single RCD that trips every circuit in the house at once.
An EICR that recommends replacement, or no spare ways for a circuit you want to add, such as an EV charger or a new kitchen.
RCBOs and why they help
Many boards fitted between the 2000s and mid-2010s are "split-load": two RCDs each protecting half the circuits. One fault can switch off half the house, often including the lights. A modern board with an RCBO on every circuit isolates only the circuit with the fault. The failed toaster takes out the kitchen sockets, not the landing lights on the way to bed.
Why testing comes first
A new board with RCD protection is less tolerant of existing faults than an old fuse box. Damp in an outside light, a damaged cable or a leaky appliance may have gone unnoticed for years. So before a new board goes in, the existing circuits should be tested. If a circuit fails, you should be told what was found and what it will take to fix before anything else happens.
What to expect on the day
Most replacements take the best part of a day, with the power off for most of it. Earthing and bonding to the water and gas pipes are checked and upgraded where needed. Every circuit is labelled, the work is notified to building control, and you receive an Electrical Installation Certificate.
It is worth planning ahead: move anything valuable out of the freezer, charge laptops and phones, and make sure the electrician can reach the board and the meter easily.
General information, not advice for your property. Electrical work should be carried out by a qualified electrician.
