UK domestic history

A short history of circuit protection in UK homes.

Ever wondered why your grandparents' house had a little tin of fuse wire in the cupboard under the stairs, and yours has a row of tidy switches? This is a plain-English tour of how the humble fuse has evolved into today's RCBOs and AFDDs — with pictures to help you recognise what you've got at home. No jargon, no maths.

Images are illustrative reference examples — real-world devices vary in brand and style.

Vintage white ceramic semi-enclosed BS 3036 rewireable fuse holder with exposed tinned copper fuse wire

1900s – 1960s (still permitted)

Semi-enclosed 'rewireable' fuses (BS 3036)

What it is: Correctly called a semi-enclosed fuse (BS 3036:1958, still a current standard) — a short piece of tinned copper fuse wire held between two screws inside a porcelain carrier. When too much current flows, the wire melts and breaks the circuit. Made in three duty categories — S1A (1 kA), S2A (2 kA) and S4A (4 kA) — depending on how much fault current they can safely interrupt.
What it protects against: Overload and short circuit only, and even then rather slowly. Because BS 3036 fuses can't be relied on to open at 1.45 × their rating within 4 hours, BS 7671 effectively requires the fuse to be no more than 0.725 × the cable's current-carrying capacity — so cables often had to be over-sized. No shock protection whatsoever.
How to spot it: Cream or brown porcelain carriers you pull out of the fuse box, coloured dots or numbers for the rating (5, 15, 20, 30, 45 A), and usually a little tin of spare fuse wire hanging nearby.
Is it still safe today?: Not banned — BS 7671 regulation 533.1.1.3 still permits semi-enclosed fuses where the prospective fault current is within the device's category — but the IET's clear preference is cartridge fuses or breakers. Older wooden or hardboard fuse boxes also fail today's rule on non-combustible enclosures (regulation 526.5). If a home still has these, a modern consumer unit is strongly recommended.

Cylindrical ceramic cartridge fuse with metal end caps

1960s – 1980s

Cartridge fuses (BS 1361 / BS 88)

What it is: A sealed ceramic tube with a fuse element inside. When a fault occurs the element burns out and the whole cartridge is replaced.
What it protects against: Overload and short circuit. Faster and more predictable than rewireable fuses, but still no shock protection.
How to spot it: Small cylindrical fuses that slot into a plastic carrier, often colour-coded by rating.
Is it still safe today?: Reliable for what they do, but very dated in a modern home. Usually replaced during a consumer unit upgrade so every circuit gets shock protection too.

Modern white DIN rail miniature circuit breaker with black toggle switch

1980s – today

MCB — Miniature Circuit Breaker

What it is: A switch that trips off automatically when the current gets too high. Once the fault is fixed, you simply switch it back on — no fuse wire, no replacements.
What it protects against: Overload and short circuit, quickly and repeatably.
How to spot it: Rows of small switches inside a modern consumer unit, each labelled with its circuit (lights, sockets, cooker, etc.).
Is it still safe today?: Still perfectly acceptable and used every day, but on their own they do not protect against electric shock. That is why they are paired with an RCD, or replaced with an RCBO.

Modern white residual current device with test button

1980s – today

RCD — Residual Current Device

What it is: Constantly compares the electricity going out to the electricity coming back. If any current 'leaks' — for example, through a person touching a live part — it cuts the power in a fraction of a second.
What it protects against: Electric shock and earth-leakage fires. It does not on its own protect against overload.
How to spot it: A larger switch, usually in the middle of the consumer unit, with a small 'T' or 'Test' button. Pressing it should trip everything on that side of the board.
Is it still safe today?: Very effective, but one RCD protecting many circuits means one small fault takes half the house off. Modern practice is to use RCBOs instead.

Modern single-module RCBO combined circuit breaker with test button

2000s – today

RCBO — combined breaker + RCD

What it is: Two protections in one neat unit: it trips on overload and short circuit like an MCB, and on earth leakage like an RCD.
What it protects against: Overload, short circuit and electric shock — all on that one circuit only.
How to spot it: Each switch in the consumer unit has its own little test button. A fault on the kettle circuit doesn't take the lights out.
Is it still safe today?: Today's standard for new installations and consumer unit changes under BS 7671. Highly recommended for any upgrade.

Modern arc fault detection device with LED indicator and test button

2020s – today

AFDD — Arc Fault Detection Device

What it is: A modern AFDD is an MCB, an RCBO and an arc fault detection device all rolled into one single-module unit. As well as tripping on overload, short circuit and earth leakage, it 'listens' to the electrical signal for the tell-tale signature of an arc — the tiny sparks caused by loose terminals, damaged cables, or rodent-chewed insulation — and disconnects before it can start a fire.
What it protects against: Overload, short circuit, electric shock (earth leakage) and — uniquely — fires caused by arcing faults, which older devices simply cannot detect.
How to spot it: Chunkier than an MCB or RCBO, often with an LED indicator on the front showing why it tripped.
Is it still safe today?: Required by BS 7671 in certain higher-risk buildings (HMOs, care homes, student accommodation, high-rise), and strongly recommended everywhere else — especially bedrooms and hard-to-reach wiring.

In one sentence

Old fuses only stopped wires overheating; modern devices also stop electric shocks and, with AFDDs, even hidden fires. If your fuse box still looks like the top two pictures on this page, it is well worth a chat.