Consumer Unit Upgrade: What to Expect When Replacing Your Fuse Board

The consumer unit — the fuse board — is the central hub of your home’s electrical installation. It contains the protection devices that are supposed to disconnect power before a fault becomes a fire or a fatality. An old fuse board with ceramic rewirable fuses or an early MCB board with no RCD protection is not doing this job adequately by modern standards.

A consumer unit upgrade is the single most impactful electrical safety improvement available for an older UK property. This guide explains what changes when you upgrade, what the installation involves, how long it takes, and what you should expect to pay.

Signs Your Consumer Unit Needs Upgrading

Rewirable ceramic fuses

The oldest type — a porcelain fuse holder containing a length of fuse wire. When a fault occurs, the wire melts and breaks the circuit. To restore power, the wire must be replaced manually.

Problems:

• No overload protection — fuse wire is often replaced with the wrong rating (thicker wire that never blows) or with inappropriate materials (nails, foil)
• No RCD protection whatsoever — earth faults and shock hazards are not detected
• The boards themselves are typically 40–50+ years old with aging insulation and connections
• Fail inspection — will receive a C2 finding on any EICR

Early MCB boards (no RCD)

Boards from the 1980s and 1990s often have miniature circuit breakers (MCBs) but no residual current devices. MCBs protect against overcurrent and short circuit but provide no protection against earth faults that are not large enough to trip the MCB.

Problems:

• No 30 mA RCD protection on socket circuits — mandatory under current BS 7671
• No RCD on bathroom or outdoor circuits
• Often under-specified for current circuit loads (kitchen circuits, EV chargers added later)
• Will receive C2 findings for missing RCD protection on any EICR

Split-load boards with a single RCD

An improvement over no-RCD boards, but the entire protected half of the board trips when one fault occurs. A nuisance trip on a freezer circuit at 2 am turns off everything on that RCD — the freezer, fridge, and potentially the smoke alarm circuit.

Problem: No circuit selectivity — one fault affects many circuits.

Non-metal enclosure (pre-2016)

Since January 2016, BS 7671 (17th Edition Amendment 3) has required consumer unit enclosures to be metal (or constructed from a non-combustible material). Plastic consumer units installed after this date are non-compliant. Older plastic boards are not required to be replaced immediately, but any new installation work must use a compliant metal CU.

What a Modern Consumer Unit Contains

A fully upgraded modern consumer unit contains:

Metal enclosure

Fire-resistant metal cabinet that contains any arc flash or overheating within the board, preventing it from igniting surrounding materials.

Main isolator switch

A 100 A double-pole switch (or 80 A for smaller installations) that disconnects both live and neutral to all circuits simultaneously. Essential for safe access to the board for maintenance.

RCBOs for every circuit

The gold standard in modern domestic installations: one RCBO per circuit, providing both overcurrent protection (like an MCB) and 30 mA earth leakage protection (like an RCD) on a per-circuit basis.

Advantage over split-load or whole-board RCD: a fault on the kitchen socket circuit trips only the kitchen circuit RCBO — not the lighting, not the freezer, not the alarm. This is the correct approach for selectivity.

Related: What Is an RCBO? The Difference Between RCD, MCB and RCBO Explained

Arc Fault Detection Devices (AFDDs) — optional

The 18th Edition of BS 7671 (2018) introduced guidance on AFDDs (Arc Fault Detection Devices) for high-risk locations — bedroom circuits in particular. AFDDs detect the electrical signature of a dangerous arc (which can cause fires without tripping a normal MCB or RCD) and disconnect the circuit.

AFDDs are not yet mandatory in all domestic circuits but are recommended for bedroom and living-area socket circuits. They significantly add to cost.

What Stays the Same

A consumer unit upgrade replaces only the board and its protection devices. The fixed wiring in the walls, floors, and ceilings is not changed. The circuits remain as they are — the same cable, the same sockets, the same light fittings.

This is important: upgrading the consumer unit does not make old wiring new. An EICR of the full installation may still reveal C2 findings in the wiring beyond the board. The upgrade addresses protection; an EICR addresses the condition of the entire installation.

Related: When to Get an EICR: The Complete Electrical Safety Inspection Guide

The Upgrade Process: Step by Step

1. Survey and design

A registered electrician visits to:

• Identify all existing circuits (count and label)
• Check the incoming supply fuse rating (typically 60–100 A)
• Confirm the earthing arrangement (TN-C-S, TN-S, or TT)
• Identify any circuits requiring special protection (bathroom, kitchen, outdoor, EV charger)
• Confirm whether an EICR of the existing installation is to be carried out alongside

2. Isolation and removal

On the installation day:

• The DNO (Distribution Network Operator) supply fuse at the cut-out is not touched — only the DNO can access this. The electrician works from the meter tails onward.
• The old consumer unit is isolated by removing the main incoming fuse from the cut-out (your electrician has the correct tool for this, or the DNO may need to attend for very old cut-outs)
• Each circuit cable is carefully labelled before disconnection from the old board

3. New board installation

• The new metal consumer unit is fixed to the wall in the same location (or repositioned if required — typically near the meter)
• Each circuit cable is reconnected to the correct new RCBO
• Earth and neutral conductors are connected to the respective bars
• The main switch receives the meter tails

4. Testing

Before power is restored:

• Insulation resistance test on every circuit — confirms cables are not damaged or shorted
• Earth continuity — from every circuit’s CPC through to the MET and back to source
• Polarity — live, neutral, earth correctly identified at every point
• RCD/RCBO operation — all devices trip at or below 30 mA
• Earth fault loop impedance (Zs) — confirms MCBs/RCBOs will disconnect fast enough

5. Certification

An Electrical Installation Certificate (EIC) is issued for the new consumer unit installation. For landlords, this is one of the documents required alongside the EICR.

How Long Does It Take?

During the upgrade, the property has no electrical power. Plan for:

• No lighting (work in daylight if possible, or use battery-powered lighting)
• No heating if electric
• No refrigerator/freezer (pre-chill, minimise opening)
• Laptops and phones will need to be charged beforehand

Cost

Consumer unit upgrade costs vary by region, board size, and whether RCBOs or a split-load arrangement is used:

Always get at least two quotes from NICEIC or NAPIT registered electricians. Be wary of quotes below £300 — this rarely includes a full RCBO board with proper testing and certification.

What Affects the Price

• Number of circuits — more circuits means more RCBOs and more testing time
• RCBO vs split-load — RCBOs are more expensive per unit but provide better selectivity; a full RCBO board costs more but is superior
• EICR combined — adding an EICR of the full installation adds cost but is strongly recommended alongside an upgrade so you know the condition of the wiring the new board is protecting
• Remedial work — if the EICR reveals additional C2 findings (missing bonding, damaged cables), this adds to the job
• Location of the board — if the consumer unit is in a difficult location (under stairs, in a cupboard with no room to work) it takes longer
• Age of installation — old cable insulation may be fragile; extra care and time required

Upgrade vs Full Rewire

A consumer unit upgrade is not a rewire. If the existing wiring has significant problems (failed insulation resistance tests, extensive C1/C2 EICR findings throughout the installation, or very old rubber or lead-sheathed cables), a full rewire may be more appropriate.

Signs a rewire may be needed instead of (or as well as) a CU upgrade:

• Cables with old rubber or fabric insulation (pre-1960s) that fails insulation resistance testing
• Widespread C2 EICR findings across many circuits
• Old-style black trunking or conduit with brittle contents
• Evidence of past DIY wiring work, junction box spiders, or unsafe modifications
• Recurring RCD trips that cannot be attributed to a specific fault

A full rewire of a 3-bedroom house typically costs £4,000–£8,000 and takes 5–10 days, depending on size and complexity.

Simulate the Difference in ElectraSim

ElectraSim lets you compare old and new protection arrangements side by side:

1. Build a circuit with a simple MCB and inject an earth fault — observe that the MCB does not trip (the fault current is below the MCB’s trip threshold)
2. Replace the MCB with an RCBO and inject the same fault — the RCBO trips immediately on the 30 mA residual current
3. Add multiple circuits to a distribution board — demonstrate that an RCBO on each circuit means a fault on one circuit trips only that circuit, while others remain live

Open ElectraSim — free, no account required →

Key Points

• Rewirable fuse boards and no-RCD MCB boards will receive C2 EICR findings — upgrade needed
• Modern standard: metal enclosure + one RCBO per circuit (30 mA) for full selectivity
• Upgrade replaces the board only — wiring is not changed; combine with an EICR to check the full installation
• Typical cost: £500–£900 for a full RCBO board on a 3-bedroom house
• Typical time: one day for most domestic properties
• Always use a NICEIC, NAPIT, or ELECSA registered electrician — an EIC must be issued for the new board
• Consumer unit upgrade is Part P notifiable — a registered electrician self-certifies, or you notify Building Control

Related: Distribution Board Explained: How a Consumer Unit Is Wired

Related: What Is an MCB Breaker? How Miniature Circuit Breakers Work

Related: 5 Common Electrical Wiring Mistakes (and How to Avoid Them)