Why is my old rewireable fuse box beginning to smoke at the main terminals?
Quick answer
Smoking at the main terminals of a rewireable fuse box is almost always caused by a loose or corroded connection creating high resistance, which generates heat and can ignite surrounding insulation or the fuseboard casing itself. This is a serious fire and electrocution risk. Turn off the main switch immediately if it is safe to do so, do not attempt any DIY repairs, and call a qualified electrician today. A smoking consumer unit requires urgent professional attention and almost always means full replacement is necessary.
🏠Homeowner view
If you can see or smell smoke coming from the main terminals of your old rewireable fuse box, this is a genuine emergency and should not be treated as a minor inconvenience. The situation needs to be taken seriously right away.
What is actually happening inside the board
Your rewireable fuse box was almost certainly installed several decades ago, likely in the 1960s, 1970s or 1980s. Over that length of time, the main incoming terminals where the electricity supply connects to the board can become loose, corroded or degraded. When a terminal is not making a solid, clean electrical contact, resistance builds up at that joint. Resistance turns electrical energy into heat, and if enough heat builds up, it can scorch the surrounding plastic, melt insulation on cables and ultimately start a fire inside the board itself.
The smoke you are seeing is often burning plastic or insulated cable sheathing. In some cases it is the Bakelite or early thermoplastic casing of the fuseboard itself beginning to char.
What you should do right now
Do not touch the terminals or the wiring. These are live parts and are extremely dangerous.
If it is safe to reach the main switch on the board, switch it off. This is usually a large lever or rotary switch at the top or side of the unit.
If there is any sign of flames, leave the property immediately and call 999.
Do not restore power until a qualified electrician has inspected the board.
Call a Part P registered or NICEIC or NAPIT approved electrician as an emergency job today. Many firms offer same-day emergency call-outs.
Why this cannot be left or patched
Rewireable fuse boxes do not have the protection features that modern consumer units offer, such as residual current devices or arc fault detection. Even if an electrician tightens the terminal today, the underlying issue is that the board is old, the materials are degraded and the installation no longer meets modern safety standards. In almost every case, a smoking rewireable fuse box will need to be replaced with a modern consumer unit as a matter of urgency.
Your home insurer should also be notified, as a smoking fuseboard may affect your policy.