What is this?
Rewirable fuses are the oldest type of overcurrent protection still found in UK homes. They consist of a fuse carrier with a piece of fuse wire stretched between two terminals. When too much current flows, the wire melts and breaks the circuit. While this basic principle works, rewirable fuses have significant drawbacks compared to modern MCBs: they can be fitted with the wrong rated wire, they blow easily on startup surges, and they do not provide the precision protection of an MCB.
Common causes
- Consumer unit has not been upgraded since the property was built (typically pre-1980s)
- Fuses have been replaced with incorrect fuse wire ratings over the years
- Board is too old to accept modern MCBs as plug-in replacements
- Previous rewires have kept the old board and only replaced the cables
- Property owner is unaware that upgrades are recommended
Is it dangerous?
Rewirable fuses provide basic overcurrent protection but are less safe than MCBs. The main risk is that anyone can fit the wrong rated fuse wire — for example, using 30A wire in a 5A lighting fuse carrier. This defeats the protection entirely and could allow a fault to cause a fire. Rewirable fuses also lack RCD protection, meaning there is no defence against earth faults that cause electric shock.
Can I fix it myself?
You can replace a blown fuse wire if you know the correct rating and have the proper fuse wire. However, this is a temporary measure. The broader issue — lack of modern protection — can only be resolved by upgrading the consumer unit. Never use any wire, nail, or metallic object as a substitute for proper fuse wire.
When to call an electrician
Contact an electrician to discuss upgrading your consumer unit. While rewirable fuses are not an emergency, they provide significantly less protection than modern MCBs and RCDs. An upgrade is one of the most cost-effective safety improvements you can make to your home.
What will an electrician do?
Inspect the existing fuse box and wiring to assess condition
Remove the old fuse box with rewirable fuses
Install a new 18th Edition consumer unit with MCBs and RCD protection
Test every circuit in the property as part of the upgrade
Issue an Electrical Installation Certificate and notify Building Control
Typical cost
£350 – £600
Standard consumer unit upgrade cost. This replaces all rewirable fuses with MCBs and adds RCD protection. The price includes full testing and certification.
