What type of consumer unit do I have? A UK homeowner’s visual guide

When a circuit trips or a fuse blows, the first thing most people do is open the consumer unit — and then stare at it, unsure what they are looking at. The troubleshooting steps differ completely depending on what type of board you have. This guide helps you identify exactly what you have, what it means for your protection level, and what to do when something goes wrong.

Why the type of board matters

Your consumer unit — sometimes still called a fusebox or distribution board — is the heart of your home’s electrical protection. Every circuit in your home runs back to it. The type you have determines how that protection works, how you respond to a fault, and what level of safety technology is in place.

This is not purely academic. When you call us and describe a fault, the first question is often: what does your board look like? If you have a rewirable fuseboard, you cannot simply reset a switch — you need to check for a blown fuse wire. If you have a modern RCBO board, only one circuit will have tripped and the reset is straightforward. The procedures are different. The risks are different. And the urgency of getting an upgrade is very different depending on what you have.

The five types below are presented roughly in chronological order — oldest to newest. They represent the progression of consumer unit technology across the last 70 years of UK domestic wiring.

Type 1 — Rewirable fuseboard (pre-1980s)

Oldest technology

The rewirable fuseboard is the oldest type still found in UK homes. You will recognise it by its ceramic or Bakelite construction: a row of rectangular fuse holders, typically cream or white, with no switches, no rocker levers, and no test buttons. The board may have a main switch — a large rotary or lever switch — but the individual circuit protection is purely through fuse wire threaded through terminals inside each holder.

These boards are still found in older properties throughout Bristol and South Gloucestershire — particularly in Victorian and Edwardian terraces that have not had a full rewire. The fuse holders are typically labelled (or were once labelled) with the circuit they protect: lighting, ring main, cooker, immersion, and so on.

What to do in a fault situation

If a circuit fails and you have a rewirable board, the fuse wire on that circuit has most likely burnt through. You can identify which circuit by checking which fuse holder is warm or shows signs of discolouration. Do not attempt to rewire the fuse yourself unless you are fully confident in the process and know the correct wire gauge for that circuit. Using the wrong fuse wire rating — or any wire that comes to hand — removes the protection entirely and is a fire risk.

Call us. We can attend, identify the cause of the fault, replace the fuse wire with the correct rating, and advise on whether the underlying cause needs investigation.

Type 2 — Cartridge fuseboard (1960s–1980s)

Outdated

The cartridge fuseboard looks similar to the rewirable type at first glance — the same era of construction, the same ceramic or Bakelite holders — but instead of threaded fuse wire, each holder contains a self-contained cartridge fuse. These are torpedo-shaped ceramic cylinders, colour-coded by amp rating.

The colour coding follows a standard convention: white for 5A (lighting), blue for 15A (immersion heater), yellow for 20A, red for 30A (ring main), and green for 45A (cooker). When a fuse operates, you replace the cartridge with one of the same rating.

Slightly safer, but still outdated

The cartridge type is marginally safer than the rewirable type in one respect: you cannot inadvertently fit a fuse that is the wrong rating for the circuit, as long as you match the colour. However, the same fundamental limitation applies: there is no RCD protection, and the protection operates only on overcurrent — not on earth leakage faults that an RCD would catch.

If a fuse operates, identify the correct rating from the label or the colour of the old cartridge, fit a new cartridge of the same rating, and investigate whether the fault that caused it to blow has been resolved. If fuses are blowing repeatedly, call us — a repeat fault needs investigation, not just a replacement fuse.

Type 3 — Modern MCB board with RCD (split-load)

Most common

This is the most common type found in UK homes built or rewired from the 1990s onward. It is identifiable by a large main switch at the top or left of the board, then one or two larger switches labelled “RCD” covering the circuits, and beneath those, a row of smaller rocker switches — the MCBs (Miniature Circuit Breakers) — each labelled with its circuit.

On a single-RCD board, all circuits are covered by one RCD. On the more common split-load arrangement, there are two RCDs, each covering half the MCBs. The purpose of the split is straightforward: if a fault trips one RCD, only half the circuits go off — the other half stay live. This prevents a single fault from cutting power to the whole property. In practice, one RCD side typically covers ring main and socket circuits, while the other covers lighting — though layouts vary.

Understanding what the RCD covers

On a split-load board, the RCD only protects the MCBs wired behind it. If your lighting is on the non-RCD side (which happens in some older configurations), those circuits have no residual current protection. This is explained in more detail in our article on RCD protection and why some circuits may not be covered.

What to do when an MCB trips

When an MCB trips, it flips to the middle or off position. Identify which one by working your way along the row — the tripped MCB will be in a different position from the others. Turn off or unplug any appliances on that circuit, then push the MCB back to the on position. If it trips again immediately, there is a fault on that circuit that needs investigation. Do not keep resetting it — call us. If the RCD has tripped, see our article on what to do when your RCD keeps tripping.

Type 4 — Full RCBO board

Current standard

The full RCBO board is the current gold standard for domestic consumer units and has been the standard for new installations since approximately 2018. Instead of shared RCDs covering groups of MCBs, every circuit has its own individual RCBO — a Residual Current Breaker with Overcurrent protection. The RCBO combines both functions in a single, wider device.

You can identify an RCBO board by looking at the individual circuit devices: they are noticeably wider than plain MCBs, and each one has its own small test button — a tiny circular button, usually white or grey, on the face of the device. The board will have a main switch, and then a row of these wider RCBO units, each protecting a single circuit independently.

The key advantage: fault isolation

The practical benefit of an RCBO board is fault isolation. When a fault occurs — whether overcurrent or earth leakage — only the affected circuit trips. Nothing else is affected. You do not lose lighting across half the house because a socket circuit developed a fault. You do not find yourself in the dark while resetting a board.

Every circuit also has full RCD protection, including lighting circuits. The concerns about unprotected circuits that apply to split-load MCB boards do not apply here.

For more detail on how RCBOs work and why they differ from standard MCBs, see our article on what is an RCBO and how does it work.

Type 5 — AFDD board (arc fault detection)

Newest technology

AFDD stands for Arc Fault Detection Device. This is the newest generation of consumer unit technology, adding a further layer of protection on top of the RCBO’s overcurrent and residual current functions. An AFDD can detect dangerous arcing faults — the kind caused by damaged, pinched, or deteriorating cable insulation inside a wall or under a floor, where the cable may arc without the fault current being high enough to trip a standard MCB or RCBO.

These arcing faults are a leading cause of electrical fires in the UK, and they are faults that no previous generation of protective device could detect. The AFDD monitors the waveform of the current in the circuit and identifies the signature pattern of an arc fault, even at low current levels.

When AFDD is required

AFDD protection is required under the 18th Edition Amendment 1 (2020) in specific situations: certain new-build locations including bedrooms and certain high-risk areas. It is not currently mandatory for all circuits in all properties, but the regulations continue to evolve.

If you have an AFDD board, you have the most advanced protection available. The critical instruction if any device on an AFDD board trips is: always call rather than simply resetting without investigation. An AFDD trip means the device has detected a fault that other protection would have missed. Resetting it without understanding the cause risks the device tripping again — or missing a fault that has not yet escalated to a level where the arc fault detection activates.

Still not sure what you have?

The diagrams above cover the main categories, but no two consumer unit installations look identical. Labels fade, covers are replaced, and older boards sometimes have a mixture of components. If you have looked at your board and still cannot identify it, call us on 07590 517472 and describe what you see. Our team can often help you identify the type over the phone, and we offer free assessments for customers who need us to visit.

A note on upgrading

If you have a Type 1 or Type 2 board (rewirable or cartridge), an upgrade to a modern RCBO consumer unit is a significant safety improvement and is generally straightforward for a qualified electrician to carry out. The same wiring can typically be retained and reconnected to the new board.

If you have a Type 3 split-load MCB board, whether to upgrade depends on the age and condition of the installation, how many circuits lack RCD protection, and any specific circumstances in your property. An EICR will identify the protection status of each circuit and flag any that are not meeting current standards.

For detailed guidance on whether a consumer unit upgrade is right for your situation, see our articles on consumer unit upgrades and split-load board options. You may also want to read our full guide to RCD protection and what it means for your home.