An extension adds circuits, and those circuits have to land somewhere. Whether that means a new consumer unit depends on spare ways, the protection already fitted, the condition of the existing circuits and the total load. It is worth settling this early, because a board change is easier to sequence at the start of a build than after the kitchen is fitted.
Four questions that decide it
We work through these on the survey, before anyone orders materials.
- Are there enough spare ways for the new circuits, with room left over
- Does the board provide the earth leakage protection current standards expect
- Do the existing circuits pass testing, or will a new board expose faults
- Is the incoming supply and main protective bonding adequate for the added load
When the existing board can stay
A reasonably modern board with spare ways, sound bonding and circuits that test well can usually take an extension without replacement. We add the new protective devices, test, certify and label the schedule so the board still reads correctly.
When a replacement makes sense
A rewireable fuse board, a board with no earth leakage protection, a damaged or obsolete unit, or one with no room left is a good candidate for change while the walls are open and the electrician is already on site. Doing it during the build usually costs less disruption than doing it later.
Position and access
Extensions often change where the board should live, particularly when a hallway or utility disappears into the new layout. Think about access for testing and for switching off in a hurry, and keep the board out of the back of a fitted cupboard.
Common questions
- Can you tell from a photo?
- A photo gives a strong indication of age and spare ways. Testing gives the answer on circuit condition.
- Is a board change notifiable?
- Replacing a consumer unit is commonly notifiable. Confirm the current position with your local authority building control.
- How long is the power off?
- Usually most of a working day for a domestic change, planned so you can work around it.
- Will a new board trip more?
- It can reveal existing faults an old board tolerated. That is the protection working, and we trace and fix the cause.
Send a photo of your board with your extension plans and we will tell you whether it needs changing.
Related guides
- What Affects the Cost of a Consumer Unit UpgradeTwo identical-looking boards can be very different jobs once the cover comes off.
- RCD vs RCBO: What the Difference Means at HomeThe difference is not protection quality — it is how much of your house goes dark when something leaks.
- How Much Does It Cost to Wire an ExtensionExtension electrics are priced by scope and access, not by floor area alone.