A consumer unit is the central distribution point for electricity in a UK property. Commonly called a fuse box, it takes the incoming power supply from the meter and splits it into individual circuits for lighting, sockets, cookers, and other fixed appliances, while a set of protective devices inside monitor each circuit and cut power automatically if a fault occurs.
Most homeowners only think about their consumer unit when something trips, but understanding what is inside it, which type you have, and when it actually needs replacing can save you an unnecessary call out or, more importantly, flag a genuine safety risk before it becomes one. This guide covers all of that under current wiring regulations.
What a Consumer Unit Does
A consumer unit distributes electricity from the meter into separate circuits throughout a property and automatically disconnects any circuit where a fault, overload, or earth leakage is detected, protecting people from electric shock and preventing electrical fires.
Power enters the property through the meter and reaches the consumer unit’s main switch first. From there, a busbar carries current to each individual circuit breaker, which feeds a specific part of the property, such as upstairs sockets, kitchen appliances, or an electric shower. Each of those circuits is independently monitored, so a fault in one part of the house does not necessarily bring down the whole property, depending on which protection setup is fitted.
When a fault occurs, the response is near instant. An overloaded circuit trips its breaker within milliseconds, and an earth leakage fault, the kind that can cause a fatal shock, is detected and cut by an RCD even faster, typically in under 40 milliseconds at rated current.
Components Inside a Consumer Unit
Main switch The main switch is the only manually operated isolator in the unit. Turning it off disconnects the entire property from the electricity supply, which is used before any electrical work or during an emergency.
RCD (Residual Current Device) An RCD monitors the current going out on the live wire against the current returning on the neutral wire. If there is a difference, meaning current is leaking somewhere it should not, typically through a person or a fault to earth, it disconnects the circuit. RCDs became a mandatory requirement for socket circuits in most new and rewired installations following the 17th Edition wiring regulations.
MCB (Miniature Circuit Breaker) An MCB protects a single circuit against overload and short circuit by tripping when current exceeds its rated value. Unlike an RCD, it does not detect earth leakage, only excess current.
RCBO (Residual Current Breaker with Overcurrent protection) An RCBO combines the functions of an MCB and an RCD in one device, giving each circuit both overload protection and earth fault protection independently. If a fault occurs on one circuit, only that RCBO trips, leaving every other circuit in the property unaffected.
SPD (Surge Protection Device) An SPD protects the wiring and connected equipment from voltage spikes caused by lightning strikes or grid switching events. It is not present in every consumer unit, but current regulations require an electrician to carry out a risk assessment and recommend one where the consequences of a surge would be significant, such as properties with solar panels, home offices, or extensive smart home equipment.
AFDD (Arc Fault Detection Device) An AFDD detects the specific electrical signature of arcing, a common precursor to electrical fires that neither an MCB nor an RCD is designed to catch, since arcing does not always draw enough current to trip a standard breaker. AFDDs are increasingly specified for higher risk premises such as houses in multiple occupations and buildings with sleeping accommodation.
Regular electrical and fire safety checks are usually best handled together through a single property compliance company rather than separate contractors
Types of Consumer Unit
There are two useful ways to categorise consumer units, and mixing them up is where most buying confusion comes from. One is by protection layout, meaning how RCD and MCB functions are arranged across the circuits. The other is by application, meaning what the unit is actually built for.
By protection layout
| Type | Protection arrangement | Typical use |
| Dual RCD | Circuits split across two RCDs, each covering several MCBs | Standard homes wanting cost effective, code compliant protection |
| High Integrity | Two RCDs plus a bank of dedicated RCBO ways | Homes wanting extra isolation for specific circuits, such as a home office or freezer |
| Full RCBO | Every circuit has its own RCBO | New builds, rewires, and anyone prioritising fault isolation over upfront cost |
By application
| Type | Built for |
| SPD consumer unit | Properties with solar panels, EV chargers, or sensitive electronics |
| EV consumer unit | Dedicated circuit for electric vehicle charging, usually fitted alongside or within the main unit |
| Garage or outbuilding unit | Smaller distribution boards for garages, workshops, or garden offices, often weatherproof and IP rated |
| Three phase unit | Larger properties or light commercial premises with a three phase supply |
| Metal clad unit | Required by regulation in most domestic settings since the 18th Edition, and standard in commercial premises |
In practice, most domestic consumer units bought today combine a protection layout, most commonly full RCBO or high integrity, with a metal enclosure as standard, and an SPD added where the risk assessment calls for one, rather than these being entirely separate product lines.
RCD vs RCBO
An RCD protects a group of circuits against earth leakage only and relies on separate MCBs for overload protection, while an RCBO protects a single circuit against both earth leakage and overload in one device, so a fault on one circuit does not affect the others.
| Factor | RCD (with MCBs) | RCBO |
| Circuits protected per device | Several, grouped | One |
| Fault isolation | A fault can trip every circuit on that RCD | Only the faulty circuit trips |
| Cost | Lower overall | Higher per circuit |
| Fault finding | Slower, more circuits to check | Faster, the tripped RCBO identifies the circuit |
| Best suited to | Budget conscious, straightforward installations | New builds, rewires, or homes with critical circuits like alarms and freezers |
Neither is unsafe when correctly installed and regulation compliant. The decision usually comes down to how much disruption a single fault should cause, and how much of the property’s electrical budget is being allocated to the consumer unit itself.
Fuse Box vs Consumer Unit
The terms are often used interchangeably, but they describe two different generations of the same equipment. A traditional fuse box uses rewirable fuses, meaning a thin wire that physically melts and breaks the circuit when overloaded, and has to be replaced by hand before power can be restored. A consumer unit replaces that wire with circuit breakers and RCDs that trip and can simply be switched back on once the fault is cleared, and it is now the correct technical term under BS 7671, the UK wiring regulations.
A property with rewirable fuses is not automatically unsafe, but it will not meet current RCD protection requirements and is generally considered due an upgrade, particularly if it has never been assessed by an electrician.
Signs You Need a New Consumer Unit
Book an inspection if any of the following apply:
- The unit still uses rewirable fuses rather than circuit breakers
- Socket circuits have no RCD protection at all
- Circuit breakers trip repeatedly with no obvious cause
- There is a burning smell, scorch marks, or discolouration around the unit
- You hear crackling from the unit, which indicates arcing and should be treated as urgent
- Lights dim noticeably when other appliances switch on
- You are adding a high load circuit, such as an EV charger or an electric shower, and the existing unit has no spare capacity
- The property is being sold, remortgaged, or let, and an EICR has flagged the unit as unsatisfactory
Installation Rules and Regulations
Consumer unit installation and replacement is notifiable work under Part P of the Building Regulations in England and Wales, and must be carried out or certified by a registered electrician, commonly under a scheme such as NICEIC, NAPIT, or ELECSA. Attempting the work yourself is both illegal and dangerous, since incorrect wiring inside a live distribution board is one of the more common causes of serious electrical injury.
Current requirements under BS 7671, including Amendment 3 of the 18th Edition, specify that domestic consumer units must be enclosed in non-combustible material, typically metal, following a series of house fires traced back to plastic enclosures failing during a fault. The regulations also set out mounting requirements, with switches positioned between roughly 1350mm and 1450mm from floor level to remain accessible, along with a minimum clear working space in front of the unit for safe operation and future maintenance.
On completion, you should receive an Electrical Installation Certificate confirming the work has been tested and meets current standards, which is also the document requested by insurers, mortgage lenders, and local authorities if the work is ever queried.
Consumer Unit Costs
Prices vary by protection type, number of circuits, and installation complexity. As a general guide:
| Type | Unit cost | Typical fitted cost |
| Dual RCD | £80 to £150 | £380 to £650 |
| High Integrity | £120 to £200 | £520 to £800 |
| Full RCBO | £200 to £400 | £700 to £1,200 |
| SPD protected | £250 to £450 | £850 to £1,350 |
Fitted cost includes the electrician’s labour, testing, and certification, but can rise further if the existing wiring needs remedial work, if building control notification fees apply, or if the property requires additional circuits to be added at the same time.
Maintenance and Testing
- Test each RCD monthly using its built-in test button. Power should disconnect immediately and reset cleanly.
- Arrange a periodic inspection, known as an EICR, at intervals set by property type: every 10 years for an owner occupied home, every 5 years for a rented property, and every 3 years for a caravan.
- Never open the consumer unit cover or attempt repairs yourself. All internal work requires a qualified, registered electrician.
- Keep the area in front of the unit clear and accessible, and make sure circuits are clearly labelled so any circuit can be isolated quickly in an emergency.
FAQs
What is the difference between a consumer unit and a fuse box?
A fuse box uses rewirable fuses that must be replaced by hand after tripping. A consumer unit is the modern equivalent, using circuit breakers and RCDs that can simply be reset, and is the term used in current UK wiring regulations.
How many years does a consumer unit last?
A consumer unit typically lasts 20 to 30 years, but it should be replaced sooner if it uses rewirable fuses, lacks RCD protection, or fails a periodic inspection, regardless of its age.
Can I install my own consumer unit?
No. Consumer unit installation is notifiable work under Part P of the Building Regulations and must be carried out or signed off by a registered electrician.
Do I need surge protection on my consumer unit?
It depends on the outcome of a risk assessment carried out by your electrician, but it is increasingly recommended for properties with solar panels, EV chargers, or a significant amount of sensitive electronic equipment.
What height should a consumer unit be mounted at?
Switches on the unit should sit between roughly 1350mm and 1450mm above floor level, to keep the main switch and RCDs accessible in an emergency.
Summary
A consumer unit is the modern, regulation compliant version of the fuse box, distributing electricity to individual circuits and automatically disconnecting any circuit where a fault is detected. The right type for a given property depends on how much fault isolation is wanted, how many circuits need protection, and whether surge protection or an EV charging circuit is needed. Regardless of type, installation and any internal work must be carried out by a registered electrician, and periodic testing is the only reliable way to confirm the unit is still performing as it should.