Many older UK properties still have a fuse box with rewireable (BS 3036) fuses: porcelain or plastic carriers holding a length of fuse wire. They are not illegal, but they offer much less protection than a modern consumer unit.
How they compare
| Rewireable fuse box | Modern consumer unit | |
|---|---|---|
| Overcurrent protection | Fuse wire melts; slower and less precise | MCBs or RCBOs trip quickly and consistently |
| Shock protection (RCD) | Usually none | 30mA RCD or RCBO protection |
| Resetting after a fault | Re-wire the fuse, with risk of the wrong wire being fitted | Flip the switch back |
| Enclosure | Often wood or plastic | Non-combustible (metal) enclosure in homes |
| Surge protection | None | SPD fitted where required |
Is an old fuse box legal?
Yes. BS 7671 is not retrospective, so an installation designed to an earlier edition is not automatically unsafe. An EICR assesses whether it is still safe for continued use. In practice, an old fuse box often comes with observations such as lack of RCD protection, fuse wire of the wrong rating, or deteriorating carriers, which may be coded C2 or C3 depending on the risk.
When should you upgrade?
- Your EICR records C2 items linked to the lack of RCD protection
- You are adding circuits for an EV charger, heat pump, solar PV or battery
- You are renovating a kitchen or bathroom
- Fuses blow regularly, or the board shows heat damage
Consumer unit replacement cost
Typical domestic replacements range from roughly £450–£900 for a dual-RCD board to £750–£1,200 for a full RCBO board with surge protection, with London often towards the upper end. The price includes testing every circuit first, because faults that an old fuse box tolerated, such as borrowed neutrals or poor insulation, will trip a modern board and must be fixed before it is energised. Notification under Building Regulations and an Electrical Installation Certificate should always be included.
Read RCD vs RCBO to choose the right board, then request a consumer unit upgrade.