Helpful video reference. We use Green Hawk Electrical's overview "Domestic Consumer Units 2024 — Overview, RCBOs, MCBs, AFDDs, Surge Protection" as the video reference here. Green Hawk Electrical is a UK-based company that films real installations without polished edits, covering domestic rewires, consumer unit upgrades and fault-finding across UK properties. Their 2024 consumer unit overview reflects current practice accurately.
1. The steel enclosure
Since January 2016, domestic consumer units must be housed in a non-combustible enclosure. The relevant standard is BS EN 61439-3, which requires the enclosure to pass the Glow Wire Test at 850°C. This test simulates what happens if an electrical fault inside the board produces a hot spot: the enclosure must not catch fire or allow flames to spread.
Steel is the material used in practice. Older plastic boards still function if installed before 2016, but any replacement must be steel. The board is usually finished in white or grey powder coat with a snap-off cover and clearly marked DIN rail positions.
2. The main switch (isolator)
At the far left of the board sits a double-pole 100A or 125A main switch. This is a simple on-off isolator: it disconnects both the line and neutral conductors simultaneously and nothing else. It does not trip on overload, it does not provide RCD protection. Its job is to let an electrician safely isolate the whole board before working inside.
When you need to replace a failed RCBO or carry out work on a circuit, the main switch is the starting point: switch off, confirm dead with a voltage tester, then proceed. An electrician will also advise the local Distribution Network Operator before working on anything upstream of the main switch, because the meter tails behind it remain live at all times.
3. The Surge Protection Device (SPD)
Amendment 3 to BS 7671, which came into force in 2022, introduced a risk assessment requirement for surge protection in new and rewired domestic installations. For most UK homes (connected to the overhead distribution network, with fixed wiring and electronic equipment throughout), the risk assessment results in a Type 2 SPD being required.
A Type 2 SPD clips onto the DIN rail inside the consumer unit, close to the main switch. It contains Metal Oxide Varistors (MOVs) that clamp transient overvoltages caused by nearby lightning strikes and switching events on the supply network. When the MOVs reach the end of their life, a status indicator window changes colour, showing the device needs replacing.
SPDs protect televisions, computers, smart home systems and appliances from voltage spikes that would otherwise destroy the sensitive electronics inside them. They are a meaningful protection in east Kent, where overhead rural supplies are more exposed to lightning than underground urban cables.
4. RCBOs: one per circuit
An RCBO (Residual Current Breaker with Overcurrent protection) combines the functions of an MCB (which disconnects the circuit if the current exceeds the breaker rating) and a 30mA RCD (which disconnects the circuit if more than 30mA of residual current flows to earth). A correctly specified domestic board in 2025 fits an RCBO on every circuit.
The advantage over the older split-load arrangement is selectivity. On a split-load board, a fault on any circuit protected by a given RCD trips everything on that RCD, including unrelated circuits. On an all-RCBO board, only the faulty circuit disconnects. If the bathroom circuit trips at 2am, the bedroom lights and landing socket stay on.
Typical RCBO ratings in a domestic board: 6A for smoke alarms, 10A for lighting, 16A for immersion heaters and smaller radial circuits, 32A for ring final circuits and cooker circuits. The ratings must match the cable size and the design current of the circuit.
5. AFDDs: recommended for bedrooms and living rooms
An AFDD (Arc Fault Detection Device) detects the electrical signature of a series arc: the kind of fault that occurs inside a wall when a cable is damaged, a connection is loose, or insulation has cracked. Standard overcurrent protection and RCDs cannot detect arc faults reliably because the current involved is often within the normal operating range of the circuit.
Amendment 3 recommends AFDDs on circuits supplying bedrooms, living rooms and escape routes in new-build and full-rewire work. They are not yet mandatory for existing installations, but an increasing number of electricians include them on rewire jobs, particularly in older properties with timber construction where a cable fault inside a ceiling joist could smoulder undetected for hours.
AFDDs mount on the DIN rail and replace the RCBO where fitted, so the circuit still has full RCD and overcurrent protection alongside the arc fault detection.
6. The circuit schedule
A correctly completed consumer unit must have a filled-in circuit schedule affixed to the inside of the door or cover. This schedule lists every circuit: its number on the board, a plain-English description (Downstairs sockets ring, Upstairs lights), the cable cross-section, the RCBO rating and type, and the RCD operating current.
At the end of any consumer unit installation, your electrician should also hand you an Electrical Installation Certificate (EIC) signed by the installer and an approved inspector, confirming the installation was tested and passed. Keep both documents. They are what a buyer's solicitor or an insurance assessor will ask for when you come to sell the property.
When to call us
Richard fits steel consumer unit upgrades across Sandwich, Deal, Dover, Ramsgate and Canterbury. Every installation includes an SPD, individual RCBO protection on every circuit, a completed circuit schedule and a full Electrical Installation Certificate. Typical price for a standard 12-way domestic board: from around £600 fitted.
Need a consumer unit upgrade in east Kent?
Steel board, full RCBO protection, SPD and certification all included in one fixed price.
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