What are Rewireable Fuses or Wilex Fuses?
Wilex Rewireable Fuses
- These semi-enclosed rewireable fuses are often referred to as Wilex fuses, which were common place in most properties a few decades ago, and can still be found in some domestic properties which have not been upgraded to a consumer unit with modern circuit breakers such as RCDs, MCBs and RCBOs.
Wilex fuse board
Wilex Rewireable Fuses
Replacing Fuse Wire
- The introduction of these rewireable fuses allowed circuits, such as those for lighting, ring main, immersion heaters and cookers, to be kept separate and be protected by fuses with the appropriate melting capacity.
- However, although the degree of protection cannot match that provided by RCDs, MCBs and RCBOs, one significant downside of rewireable fuses is that they can easily suffer misuse, whether by mistake or on purpose.
- For example, after a fuse has blown, the user (the homeowner or resident) will need to replace the blown fuse wire, but could easily replace it with the incorrect size.
- If no fuse wire can be found, or if replacing the fuse results in the replacement also blowing, some people have been tempted to improvise and use alternatives, such as paper clips and even a nail!
As comical as that might sound, it is a dangerous thing to do, and I strongly advise against it.
- A word of advice, therefore, would be that if you have a fuse board with rewireable fuses, make sure you have spare fuse wires kept right next to the fuse board.
- The Rewireable Fuses described here are to BS 3036
Using the correct size fuse
- For the sake of safety I will reflect here on a point I have made elsewhere about importance of using the correct value fuses...
- Fuses are designed to blow when the current passing through them exceeds their limit. So if ring main or cooker circuit is fitted with a fuse designed to protect a lower current circuit such as a lighting circuit, it is likely that the fuse will blow pretty quickly under normal use, because it was never designed to cope with that amount of current.
- On the other hand if a lighting circuit is fitted with a fuse which is intended for use on higher current carrying circuit such as for a cooker or shower, there might not be enough current flowing to blow the fuse, despite there being enough current flowing to be dangerous.
- Also note that, according to the current Electrical Installation Wiring Regulations (BS 7671:2018), the use of this type of fuse requires the current carrying capacity of the electric cables to be "derated" by 0.725 which, to most customers will mean very little. But from the perspective of an electrical installer, they need to be aware that the cables will only be able to carry about 3/4 (three quarters) of the current that similar cables in more modern installations can carry.
- These points are as applicable to the correct selection of MCBs and plug top fuses as they are to rewireable fuses, so it's important to avoid taking silly risks: Always use the correct size fuse!
- I currently hold a few spare rewireable fuse holders and sockets in case I come across customers who have cracked or broken holders or sockets, but whilst it's not so easy to buy new replacement fuse holders off the shelf, fuse wire is still readily available at outlets such as
and other popular DIY stores.
Plug-in MCBs to replace rewireable fuses
- If you have rewireable fuse in your consumer unit and want to upgrade to MCBs without replacing the entire consumer unit, there is an alternative solution... Plug in MCBs
- These plug-in MCBs simply replace your existing rewireable fuses with no other modifications necessary provided that the existing wiring and sockets are in good order.
- They offer the same level of protection that conventional B-Type MCBs provide, but because it is physically possible for someone other than an electrician to fit them, there is a risk that the wrong size plug-in MCB could be fitted for any given circuit. Likewise it is also possible to move plug-in MCBs from socket to socket. That would be a potentially dangerous thing to do, so if in any doubt, please get an electrician in to check.
- You might be tempted to fit the plug-in MCBs yourself, and there's nothing prevent you from doing so, but please remember to switch off the fuse board at the main switch first.
- DO NOT REMOVE THE FUSE BOX COVER!!!
Even with the main switch OFF, there will still be dangerous live parts which can easily be touched, so please do not remove the cover.
- It is also going to be worth considering asking an electrician to check the condition of the wiring and terminations in your fuse board.
This will almost always come with a recommendation to have the board changed to one which complies to the current wiring regulations (BS 7671 18th Edition), but at the very least you should ask for the wiring and terminations to be checked as dodgy wiring or poor terminations can result in arcing, over heating and even fire.