A consumer unit is the electrical distribution board that supplies and protects the circuits in your property. Often called a fuse box, it is where you will usually find the main switch and the protective devices for sockets, lighting and larger appliances. When it trips, buzzes, smells hot or loses power, the problem may be inside the unit or elsewhere on a circuit. We provide 24/7 emergency electrical help across London and the M25 area. If there is smoke, burning, sparking or water near electrics, switch off at the main switch only if safe to do so, keep clear and call an emergency electrician. Call 999 for a fire.
Consumer Unit
In a London flat, house or small business, the consumer unit divides the incoming electricity supply into separate circuits. These might serve downstairs sockets, upstairs lights, an electric shower or kitchen equipment. Its main switch normally disconnects the circuits supplied by that unit, but it does not make the incoming supply cables safe. Properties with solar panels, batteries or other additional supplies need particular care because switching off one point may not isolate every source.
Different protective devices do different jobs. A miniature circuit breaker, or MCB, disconnects a circuit when excessive current flows, such as during an overload or short circuit. A residual current device, or RCD, detects an imbalance that can indicate electricity leaking to earth. An RCBO combines those functions for an individual circuit. Older boards may use rewireable fuses instead. The devices fitted affect how faults show up and how much of the property loses power.
A single RCD can protect several circuits, so a fault on one appliance may switch off both sockets and lights. With individual RCBOs, a fault will generally be confined to the affected circuit. In business premises, what looks like a consumer unit may instead be a larger distribution board. Identifying the arrangement matters before deciding whether a device needs replacing, a circuit needs repair or the board itself needs upgrading.
- —A switch that will not stay on can indicate a continuing fault, rather than a faulty switch.
- —A circuit label is a useful starting point, but it should not be treated as proof that wiring is isolated.
- —The front cover must stay in place: parts behind it can remain live even with the main switch off.
Faults and symptoms you may notice
Repeated tripping is a common warning. It may happen when the oven heats up, when an outdoor socket gets wet or when several high-powered appliances run together. An RCD that trips seemingly at random may be responding to combined leakage from several items or an intermittent wiring fault. If resetting a device immediately makes it trip again, leave it off. Repeatedly resetting it does not resolve the cause and can re-energise damaged equipment.
Other symptoms need attention even if the power stays on. Crackling, a new or persistent buzzing sound, a burning-plastic smell, scorch marks or a distorted cover can point to overheating or arcing. Flickering across several circuits may indicate a connection or supply problem rather than individual lamp failures. Do not touch the enclosure to check whether it is hot, remove its cover or tighten anything inside.
A partial loss of power often points towards a circuit or protective device, whereas a completely dead property may involve the main switch, incoming supply or another upstream fault. Check whether neighbouring properties or street lighting are also affected, without approaching damaged equipment. Call 105 for a street-wide power cut. For a problem confined to your premises, an electrician can establish whether it is within your installation or needs the electricity network operator's attention.
What causes consumer unit problems, and why leaving them matters
Not every trip means the consumer unit has failed. A damaged appliance flex, moisture in an outside light, deteriorated cable insulation or a screw driven into hidden wiring can operate its protective devices. Overloading can occur when a circuit supplies more current than it was designed for. A breaker must never be replaced with a higher-rated one simply to stop nuisance tripping; its rating must suit the cable and circuit design.
Faults within the unit can include loose connections, heat-damaged terminals, worn devices or unsuitable components fitted during previous alterations. A poor connection can generate substantial heat without drawing enough current to trip an ordinary circuit breaker. Water from a plumbing leak or roof defect can also reach the board. Keep clear of a wet enclosure, and do not try to dry it out or restore power yourself.
Leaving these problems unresolved can allow damage to spread to adjacent devices and cables, increase fire risk or leave a circuit without effective protection. A protective device that repeatedly disconnects the supply is giving information that needs investigation. Equally, the absence of tripping does not prove safety. For a shop or office, interrupted refrigeration, alarms or essential equipment adds an operational concern, but restoring service must not take priority over isolating a dangerous fault.
Safe checks before an electrician attends
Start with observation, not dismantling. From a safe position, note which switches appear off, which rooms have lost power and what was running when the problem started. Take a photograph of the closed board and its labels if it is safe to approach. Tell the electrician about recent leaks, drilling, appliance changes or electrical work. These details help distinguish a circuit fault from a problem inside the unit.
Where there are no signs of heat, damage, moisture, burning or sparking, you can switch off and unplug accessible appliances on the affected socket circuit. Do not handle damaged plugs or wet equipment, and do not pull out heavy appliances to reach concealed sockets. If you understand the clearly labelled controls and can operate them safely, a single reset after unplugging suspect appliances may help identify the pattern. If it trips again, leave the circuit off.
Never remove the cover, change internal devices, bridge a fuse or work on the incoming supply. Avoid repeated resets and do not use extension leads to recreate a heavily loaded circuit elsewhere. If smoke, burning, sparking or water is present near electrics, switch off at the main switch only if safe to do so, keep clear and call an emergency electrician. Call 999 for a fire; do not approach the board to isolate it if doing so puts you at risk.
How an electrician repairs or replaces a consumer unit
An electrician first establishes the symptoms and checks the installation before arranging safe isolation and proving the relevant parts dead. Testing may include insulation resistance, protective conductor continuity and operation of RCD protection. Appliances and circuit sections may need to be disconnected to trace an intermittent fault. Where damage involves supply equipment, sealed fuses or metering, the appropriate network operator or meter operator may need to be involved.
Repair may be suitable when the enclosure and connections remain sound and an appropriate compatible replacement device is available. Heat-damaged wiring requires assessment as well as replacement of the visibly affected part. Replacement of the whole unit may be appropriate where damage is extensive, components are unsuitable or the protective arrangement needs upgrading. Age alone does not determine the answer: condition, test results and the intended use of the installation all matter.
For replacement, the electrician assesses the supply, earthing, bonding, circuit condition and required protective devices against the relevant requirements of BS 7671, the IET Wiring Regulations. Existing wiring defects may need correcting before circuits can be reconnected. The work involves a planned interruption to the circuits supplied by the board, followed by inspection, testing, labelling and electrical certification, with Building Regulations notification where applicable. In London flats and commercial buildings around the M25, access to communal intake rooms or separate supply isolation may also need arranging.
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Frequently asked questions
Is a consumer unit the same as a fuse box?
People often use both names for the board that distributes electricity around a property. Strictly, an older fuse box uses fuses, while a modern consumer unit generally contains circuit breakers and residual current protection. The name tells you less than the actual devices, condition and test results, so an assessment should focus on those rather than appearance alone.
Why does the consumer unit trip when nothing is switched on?
Some equipment remains connected even when it appears off, including boilers, fridge freezers and appliances in standby. Fixed wiring faults, moisture and combined earth leakage can also operate an RCD. A neutral-to-earth fault may cause confusing symptoms across shared protection. Leave a repeatedly tripping device off and have the affected circuits tested rather than assuming the board is defective.
Does an old plastic consumer unit have to be replaced?
A plastic enclosure alone does not automatically mean an existing consumer unit must be replaced. Its condition, location, protective devices and any evidence of overheating need consideration. Requirements for new work are not a blanket instruction to replace every older board. An electrician can explain whether continued use, a specific repair or replacement is appropriate following inspection and testing.
Can a consumer unit be replaced without rewiring the property?
Often, existing circuits can remain, provided their condition and test results make them suitable for reconnection. Replacing the board does not correct damaged cables, missing protective conductors or other defects elsewhere. Testing may reveal repairs or partial rewiring that are necessary. The scope should be explained before reconnection, including any circuits that must remain isolated.
What should I tell an emergency electrician about the fault?
Describe whether all power or only certain circuits have failed, which device has tripped and whether an appliance or leak preceded the problem. Mention any smell, noise, visible damage or additional supply such as solar panels. Explain access arrangements, especially in flats or locked commercial premises, and identify essential equipment affected. Do not approach an unsafe board just to collect details.