The consumer unit is the box the incoming supply enters and the circuits leave: main switch, protective devices, and in a modern unit residual current protection for the circuits that need it. Replacing one is priced on the number of circuits and on what the earthing and bonding arrangements turn out to be, both of which are knowable before anyone quotes.
What a consumer unit does
It divides the supply into circuits and protects each one. The main switch isolates everything; the protective devices disconnect a circuit that draws too much current; residual current devices disconnect when current leaks to earth, which is the protection that matters if somebody touches a live part or a cable is cut. A unit with none of the last is the usual reason for an upgrade.
What the quote should include
The unit itself and its devices, reconnection and testing of every circuit, the installation certificate, the circuit chart, notification under Part P, and making good where the old board came off. A quote that names only the unit and the labour will meet the rest as extras, and the testing is not optional.
The variables that move it most
Circuit count. Whether the meter tails, main earthing conductor and bonding need upgrading to current sizes, which is common on older properties and is real work in its own right. Whether the position of the board has to change. And whether the supplier has to attend to pull the fuse, which is a scheduling problem more than a cost.
Why testing can add to the bill
Every circuit is tested after reconnection, and a circuit that fails cannot simply be reconnected and forgotten. Older properties turn up borrowed neutrals, damaged cables and undersized earths at this point. A good electrician warns you it is possible before starting rather than presenting it as a surprise afterwards.
Upgrade against replacement
An upgrade normally means the same thing: you cannot usefully add modern protection to an old rewireable board. Where the existing unit is serviceable, adding an RCD to a single circuit or replacing a device can be a legitimate smaller job, and an inspector who suggests one rather than a full replacement is worth listening to.
Questions people ask about consumer unit replacement cost
What is a consumer unit?
The board where the electricity supply enters the property and is divided into circuits, containing the main switch and the protective devices for each circuit.
Is a consumer unit the same as a fuse box?
In everyday use, yes. Fuse box usually means an older rewireable board, and consumer unit the modern equivalent with circuit breakers and residual current protection.
Why does the earthing and bonding affect the price?
Because a new unit can only be certified if the earthing arrangement and the main bonding meet current requirements, and upgrading them is separate work.
Do I need a certificate afterwards?
Yes. Replacing the unit means testing and certifying the installation, and the work is notifiable under Part P in England and Wales.