Fuse Ratings Guide: BS 1362 Plug Fuses, Circuit Fuses & Colour Codes
UK plug fuses (13A plugs) are rated 3A (red), 5A (black), or 13A (brown) to BS 1362. Rule of thumb: fit the smallest fuse that allows the appliance to run without blowing — for most appliances under 700W, use 3A; for 700W–3000W, use 13A; there is rarely a need for 5A. Circuit fuses (MCBs and fuses in the consumer unit) are colour-coded to BS EN 60898/BS 3036: Type B (white/tan), Type C (grey), Type D (red); older rewirable fuses: 5A (white), 15A (blue), 20A (yellow), 30A (red), 45A (green).
Summary
Fuses are the most misunderstood part of basic electrical safety. Many homeowners fit the nearest available fuse when one blows rather than the correct rating — this is potentially dangerous. Electricians must be able to quickly identify the correct fuse rating for plug-top fuses, consumer unit fuses, cartridge fuses, and miniature circuit breakers (MCBs), and explain the difference to customers.
This article covers all three fuse contexts relevant to UK domestic and light commercial work: plug fuses (13A plug top), consumer unit (MCBs, RCBOs, and older rewirable/cartridge fuses), and the BS colour coding systems.
Key Facts
- BS 1362 plug fuses — flat-pin 13A plug top fuses; available in 1A, 2A, 3A, 5A, 13A; the 3A and 13A are overwhelmingly standard; 5A is relatively uncommon; fuses must be marked BS 1362 and carry Kitemark
- 3A fuse (red) — for appliances up to approximately 700W; e.g., table lamp, phone charger, broadband router, small TV, radio, slow cooker (some)
- 5A fuse (black) — for appliances approximately 700W–1200W; not commonly used; sometimes fitted in older appliances; not standard in current practice
- 13A fuse (brown) — for appliances approximately 700W–3000W; e.g., kettle, toaster, iron, microwave, vacuum cleaner, hairdryer, electric drill
- Oversizing is dangerous — fitting a 13A fuse in an appliance rated for 3A means the flex could catch fire before the fuse blows; always use the smallest correct fuse
- MCB types (BS EN 60898) — Type B: trips at 3–5× rated current; standard for domestic lighting and socket circuits; Type C: trips at 5–10×; suitable for appliances with moderate inrush (motors, fluorescent lights); Type D: trips at 10–20×; specialist use (large motors, welders)
- MCB ratings — 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, 63A; domestic circuits: 6A (lighting), 16A or 20A (radial socket circuit), 32A (ring final circuit or shower), 40A (cooker circuit)
- RCBO — combined RCD + MCB in one module; protects a single circuit for both overcurrent and earth fault; increasingly used in new installations
- Rewirable fuses (older consumer units) — 5A (white): lighting; 15A (blue): immersion heater or 15A ring; 20A (yellow): cooker or ring; 30A (red): ring final or cooker; 45A (green): shower or cooker
- HRC (High Rupturing Capacity) cartridge fuses — used in older consumer units as replacement for rewirable; same colour coding as rewirable; HRC fuses should not be replaced with wrong ratings; rating is printed on the fuse barrel
- Fuse wire for rewirable fuses — if replacing fuse wire, use only the correct ampere-rated wire; do not use any available wire (a common dangerous DIY error); strands of copper wire, mains flex conductor, or foil are never acceptable substitutes
- CEE 7/4 (Schuko) plugs — used for some imported appliances; do not use UK 13A plug fuses with Schuko adaptors; Schuko sockets provide overcurrent protection via the circuit; no in-plug fuse
- Consumer unit main fuse — the service head (cut-out fuse) is owned and maintained by the DNO; typically 60A, 80A, or 100A; never touch or interfere with the cut-out; report to DNO if faulty
Quick Reference Table
Spending too long on quotes? squote turns a 2-minute voice recording into a professional quote.
Try squote free →| Appliance | Typical Power | Correct Plug Fuse | Fuse Colour (BS 1362) |
|---|---|---|---|
| LED lamp (single) | <10W | 3A | Red |
| Phone charger, router | <20W | 3A | Red |
| Table lamp (LED) | 40–60W | 3A | Red |
| Laptop charger | 45–90W | 3A | Red |
| Flat screen TV | 50–200W | 3A | Red |
| Desktop computer | 200–500W | 3A | Red |
| Slow cooker | 150–300W | 3A | Red |
| Small refrigerator | 100–150W | 3A | Red |
| Large fridge-freezer | 200–400W | 13A* | Brown |
| Microwave | 700–1200W | 13A | Brown |
| Kettle | 1800–3000W | 13A | Brown |
| Toaster | 800–2000W | 13A | Brown |
| Iron | 1000–2400W | 13A | Brown |
| Hairdryer | 1000–2000W | 13A | Brown |
| Vacuum cleaner | 900–2400W | 13A | Brown |
| Electric drill | 600–1200W | 13A | Brown |
*Large refrigerators: despite being under 700W steady-state, they have a start-up motor current spike that can blow 3A fuses — 13A is normal.
| MCB Type | Trip Range | Typical Application |
|---|---|---|
| Type B | 3–5× rated current | Domestic lighting; sockets; standard loads |
| Type C | 5–10× | Motor loads; some appliances with inrush |
| Type D | 10–20× | Large motors; welding; specialist industrial |
| Consumer Unit Fuse Colour | Rating | Typical Circuit |
|---|---|---|
| White | 5A | Lighting circuits |
| Blue | 15A | Immersion heater; older ring circuits |
| Yellow | 20A | Cooker circuits; some radial socket circuits |
| Red | 30A | Ring final circuit (sockets); shower |
| Green | 45A | Electric shower; cooker (large) |
Detailed Guidance
Calculating the Correct Plug Fuse Rating
The correct fuse is the smallest available that is larger than the appliance's steady-state running current:
- Find the appliance's power rating (watts) from the label or manual
- Divide by 230V (UK mains): Current (A) = Power (W) ÷ 230
- Choose the next fuse size up from this current: 3A, 5A, or 13A
Example: Kettle rated 2200W: 2200 ÷ 230 = 9.6A → next size up is 13A → fit 13A fuse Lamp rated 60W: 60 ÷ 230 = 0.26A → next size up is 3A → fit 3A fuse Electric blanket rated 100W: 100 ÷ 230 = 0.43A → fit 3A fuse
Motor loads: For appliances with electric motors (vacuum cleaners, refrigerators, power tools), the start-up current is 3–7× the running current. This rarely affects the fuse selection for 13A fuses (which are large enough to accommodate start-up) but can affect 3A — a marginal 3A choice for a motor load may blow on start-up; fit 13A in that case.
Consumer Unit Fuse Identification
Modern MCB consumer units: MCBs are marked with their rating (6, 10, 16, 20, 32, 40A) and type (B, C, D) on the front face. The rating is legally required to be visible. Do not rely on colour alone for modern MCBs — check the printed rating.
Older cartridge fuse boards: Colour-coded cartridge fuses as per the table above. The barrel is marked with the rating. When replacing:
- Always isolate the circuit (switch off the MCB/switch if on a dual board)
- Pull out the fuse holder
- Check the rating printed on the old fuse before discarding
- Fit exact replacement rating and type; never substitute
Rewirable fuse boards: Now very old technology (pre-1990s). When replacing fuse wire:
- Isolate the circuit at the main switch
- Remove the fuse carrier
- Find the printed rating on the carrier (usually embossed or on a label)
- Remove all remnants of old wire
- Thread correctly rated fuse wire through the carrier; wrap once around each terminal screw; tighten firmly; trim excess
- Replace carrier and restore power
- Record on EICR/periodic inspection
Note: If you encounter a rewirable fuse board, advise the customer that consumer unit replacement is strongly recommended. Modern split-load consumer units with RCD protection provide significantly better protection. Rewirable fuse boards are likely to fail an EICR with a C3 observation or C2 if earthing/bonding is also deficient.
Fuse Wire Substitution — The Danger
One of the most dangerous DIY electrical errors is substituting inappropriate materials for blown fuse wire. Common examples found in old installations:
- Copper flex conductor strands wound around terminals
- Aluminium foil (crisp packet) bridging the fuse holder
- Bare copper wire of unknown rating
These substitutes do not blow when overloaded — they may glow, start a fire, or allow a fault to persist and damage equipment. If found, replace immediately with correctly rated fuse wire (or ideally replace the consumer unit).
RCBO vs MCB vs RCD
MCB: Protects against overcurrent and short circuit on a single circuit. Does not protect against earth fault (person touching a live conductor).
RCD: Protects against earth fault (residual current imbalance between live and neutral). Does not protect against overload or short circuit.
RCBO: Combines both protections in a single device per circuit. More expensive (£12–25 each vs £3–8 for MCB). Provides the best protection. Required for certain circuits (sockets in a bathroom, outdoor circuits, certain kitchen circuits) under BS 7671 18th Edition.
Frequently Asked Questions
A 13A fuse keeps blowing in my extension lead. What's wrong?
The extension lead is overloaded — the total connected load exceeds 13A (3,000W). Check the total wattage of all appliances plugged into the extension. The 13A is a safety device protecting the extension lead's flex (usually rated 13A); blowing the fuse is the correct protective action. Do not replace with a higher-rated fuse — instead, reduce the connected load or use a more powerful outlet (hardwired socket circuit).
I can't find the wattage of my appliance. How do I choose the right fuse?
Check the back of the appliance for a label showing current consumption (in amps) directly. If the label shows amps rather than watts, fit the smallest fuse above that rating. If you genuinely cannot determine the rating, fit a 13A fuse as the conservative choice for mains-connected equipment, but be aware that this means overheating faults may not be detected as quickly on a lower-draw appliance.
Can I fit a 3A fuse in a computer?
Yes — most desktop computers draw 150–300W in typical use (0.65–1.3A), well within 3A. Check the nameplate; some high-performance workstations or gaming PCs with large power supplies draw more. The power supply label shows maximum draw — use that for your calculation.
Regulations & Standards
BS 1362:2003 — Specification for general purpose fuses; plug fuses; ½" and 1¼" cartridge fuses
BS EN 60898-1 — Circuit breakers for overcurrent protection; MCB ratings and types
BS 7671:2018+A2:2022 (IET Wiring Regulations 18th Edition) — Overcurrent protection; circuit design
IET: Understanding BS 7671 — IET Wiring Regulations reference
Electrical Safety First — Consumer guidance on fuses and safety
BSI Group: BS 1362 — Buy BS 1362 and related standards from BSI
socket circuits — Ring final and radial circuit design and protection
testing commissioning — MCB and protection device testing
consumer unit upgrade — Replacing rewirable fuse boards with modern units
Got a question this article doesn't answer? Squotey knows building regs, pricing and trade best practice.
Ask Squotey free →This article was generated and fact-checked using AI, with corrections from the community. If you spot anything wrong, please . See our Terms of Use.