What Is a Consumer Unit? Fuse Boxes and Switches Explained
Identify the board, understand its switches and labels, and see what inspection and testing can establish about its condition.
By EICR Certificates London · Updated 1 November 2026
A consumer unit is the electrical distribution board in a home, containing the main switch and protective devices for its circuits. It distributes power to lighting, sockets and other fixed electrical equipment. Depending on its arrangement, you may see miniature circuit breakers (MCBs), residual current devices (RCDs) or other protection.
EICR Certificates London explains these components using the terminology of the IET Wiring Regulations, BS 7671:2018+A4:2026. Identification means reading visible labels and recognising accessible controls without removing the fixed cover. A modern appearance cannot establish whether the installation would receive a satisfactory Electrical Installation Condition Report (EICR).
What Does a Consumer Unit Look Like, and Where Might It Be?
A consumer unit usually looks like a wall-mounted enclosure containing a row of labelled switches or fuse carriers. It may be in a cupboard, hallway, garage or another accessible service position. The electricity meter records consumption; sealed supplier or distribution network operator equipment has a separate role. A home can have multiple boards, including one fed through a sub-main.
- Look for circuit descriptions associated with protective devices, rather than a consumption display.
- Check that identification relates to your dwelling; nearby communal equipment may serve another installation.
- Use only normally accessible information. Do not open communal cupboards or handle sealed supply equipment.
Is a Consumer Unit the Same as a Fuse Box?
People often use ‘consumer unit’ and ‘fuse box’ for the same household equipment, although a traditional fuse box uses fuses and a modern consumer unit usually uses circuit breakers.
| Everyday description | Typical visible feature | What that feature cannot establish |
|---|---|---|
| Traditional fuse box | Fuse carriers, sometimes BS 3036 rewireable types. | Whether separate RCD protection exists elsewhere. |
| Shared-RCD board | MCBs grouped under one or two RCDs. | Whether every circuit has suitable protection. |
| RCBO board | Individual combined protective devices. | Whether connections and wiring are sound. |
These arrangements are neither a dependable timeline nor a safety ranking. Metal or plastic enclosure material alone cannot determine condition. Requirements for new work do not automatically make an existing plastic board unsafe.
What Do the Parts of a Consumer Unit Do?
The main switch controls the supply through the board, while its fuses and protective devices disconnect circuits under the conditions they are designed to detect. Devices vary between installations: shared RCD protection and individual RCBOs are alternative arrangements. For the detailed comparison, see RCD, RCBO, MCB and RCCB explained.
| Visible part | Purpose | What it does not tell you |
|---|---|---|
| Main switch | Switches the supply passing through it to the board’s circuits. | An “off” position does not prove all internal parts are dead. |
| Fuse or MCB | Protects a circuit against overcurrent, including overload and short circuit. | Its presence does not establish residual-current protection or correct selection. |
| RCD/RCCB | Detects residual-current imbalance and disconnects; may serve several circuits. An RCCB has no integral overcurrent protection. | A visible test button does not demonstrate satisfactory instrument test results. |
| RCBO | Combines residual-current and overcurrent protection, commonly for one circuit. | Its appearance cannot confirm suitability or the connected wiring’s condition. |
| Circuit labels and chart | Identify intended circuit destinations and device associations. | Descriptions may be incomplete or no longer accurate. |
| Enclosure and blanking pieces | Restrict access to internal parts, including through unused openings. | An intact exterior cannot establish the condition of hidden connections. |
Read identification and model information rather than relying on colour, width or position. An MCB cannot substitute for residual-current protection.
What Does the Main Switch Turn Off?
The main switch disconnects the circuits supplied through it, but switching it off does not prove that every part of the consumer unit is dead. Incoming connections can remain live, another board may have an independent supply, and additional power sources can affect isolation arrangements. Safe isolation is a professional process that includes establishing and verifying the electrical state with suitable equipment. It involves more than observing a switch position, as HSE’s Electricity at Work: Safe Working Practices explains.
What Is the Surge Protection Device in the Board?
A surge protection device, or SPD, limits transient overvoltages and performs a different job from an RCD or circuit breaker. Read about consumer unit surge protection for its application. Some SPDs have a condition indicator; its meaning depends on the manufacturer’s instructions, with no universal colour rule. Some boards also contain arc fault detection devices.
- SPD: limits brief voltage surges; it does not prevent damage from every possible surge.
- AFDD: detects characteristics of dangerous electrical arcing and disconnects the affected circuit.
How Does Earthing Work With the Consumer Unit?
Earthing provides a path for fault current so protective devices can disconnect the supply when required. Circuit protective conductors connect to the main earthing terminal, which need not be inside the board. An earthing conductor connects that terminal to the means of earthing. See electrical earthing explained.
Protective bonding connects relevant incoming conductive services to the earthing system to limit dangerous voltage differences. Switch positions cannot verify these connections, and RCDs do not replace protective earthing.
For replacement work, see consumer unit and fuse box upgrades in London.
For concerns about an old fuse box or missing RCD protection, see the assessment guidance.
How Do You Read Circuit Labels and Device Markings?
Circuit labels describe what a circuit supplies, while device markings identify the protective device and its ratings. Manufacturer references, current ratings and residual-current markings describe different characteristics; see RCD and RCBO types, symbols and markings.
| Label | Marking | What it tells you |
|---|---|---|
| Circuit description | “Lights” or “Sockets” — illustrative. | The intended use; one circuit may cover several rooms. |
| Device identification | Manufacturer reference and current rating. | The device specification, rather than its circuit’s destination. |
| Residual-current information | Rated sensitivity, type symbols and test-button identification. | Features to interpret using the relevant instructions. |
Labels can be outdated, and a test button is not evidence of a completed inspection. Ask an electrician to trace and record unclear circuits rather than experimenting with unidentified switches. Verified information belongs in the circuit records and schedules.
What Do Inspection and Certificates Tell You About the Board?
An EICR reports the installation’s condition at inspection, while an Electrical Installation Certificate records the new electrical work it covers. See EICR, EIC and Minor Works certificates explained for their different purposes.
| Document | Purpose | Limit |
|---|---|---|
| EICR | Records condition, observations and test results within the inspection’s scope. | Does not certify replacement work or provide notification. |
| Electrical Installation Certificate | Records design, construction, inspection and testing of work such as a board replacement, with schedules. | Does not certify unrelated existing work as new. |
| Building Regulations compliance documentation | Records compliance through the applicable notification route. | Is distinct from electrical certification. |
Replacing the board is notifiable in England under the framework described in GOV.UK’s Approved Document P. Notification can use an appropriate competent person scheme or building control route; see Part P and notifiable electrical work. A Minor Works certificate is insufficient for this replacement.
Arrange an EICR or Discuss Consumer Unit Work in London
EICR Certificates London provides EICRs and consumer unit upgrade work across Greater London. Qualified, insured electricians. Your EICR is carried out by a NICEIC-registered engineer. Open 8am to 10pm, seven days a week. Upgrade work is quoted for the agreed scope.
Have the property location, reason for your enquiry and any existing report observations ready. Discuss Your Consumer Unit by phone or contact EICR Certificates London with those details.
Consumer Unit Questions Homeowners Ask
These answers cover choosing a board, existing wiring, replacement costs and situations that need professional attention.
How Much Does It Cost to Get a Consumer Unit Fitted?
Consumer unit replacement is quoted for the property because circuit numbers, protective devices, existing defects and access affect the work. Ask for the board, devices, installation, pre-upgrade testing, certification, notification and separately scoped remedials to be identified. These inclusions provide the basis for comparing consumer unit and fuse box replacement costs.
Can a New Consumer Unit Be Fitted to Old Wiring?
Existing wiring can sometimes remain, but inspection and testing must establish whether it is suitable for connection to the new consumer unit. Assessment includes insulation resistance, earthing, circuit protective conductor continuity and existing defects. Changing the board does not renew cables; faults may need separate correction. Age or photographs cannot establish suitability.
Can I Replace a Consumer Unit Myself?
Consumer unit replacement requires competent electrical design, safe isolation, installation and testing, and it is notifiable work in England. Use a competent electrician who can provide an Electrical Installation Certificate and arrange the appropriate notification route. Recognising switches does not establish competence to work inside the enclosure, where live connections may remain present.
How Do I Know What Consumer Unit I Need?
The appropriate consumer unit depends on the installation’s circuits, supply, protective requirements and planned additions. Spare ways provide device space, not additional supply capacity. An electrician assesses maximum demand and specifies a compatible assembly and devices, using the relevant BS EN 61439-3 requirements. Components are not necessarily compatible simply because they physically fit.
What If a Fuse Box Switch Will Not Reset?
A switch that will not reset or immediately trips again needs the cause investigated rather than repeated attempts to force it on. An MCB, RCD or RCBO may be responding to an unresolved fault; its position cannot identify the cause. Follow the guidance for a trip switch or RCD that keeps tripping.
What If I Can Smell Burning Near the Consumer Unit?
A burning smell near the consumer unit needs urgent attention, and you should not touch or open the board to investigate. Keep clear and obtain urgent professional help. If there is smoke or fire, leave the property and call 999. See the dedicated guidance on burning smells or scorching around electrics.