Quick answer: Use a fused connection unit (FCU, or "fused spur") for fixed appliances that stay permanently wired in — boilers, towel rails, extractor fans, wall-mounted hair dryers, hand dryers, under-counter fridges in commercial settings. Use a 13A plug socket for anything the user plugs in and unplugs. The FCU puts a dedicated fuse and (on switched models) an isolation switch next to the appliance, which BS 7671 expects for fixed equipment.
Fused spur vs plug socket at a glance
| Factor | Fused connection unit | 13A plug socket |
|---|---|---|
| Connection | Hard-wired, permanent | Plug-in, removable |
| Fuse | In the unit (3A/5A/13A to suit appliance) | In the plug |
| Isolation | Switched models isolate at the point of use | Unplug or switch off socket |
| Typical uses | Boilers, extractor fans, towel rails, wall heaters, hand/hair dryers, alarms | Kettles, lamps, TVs, chargers, portable appliances |
| Flex outlet option | Yes — cable exits through the front plate | No |
Switched, unswitched or neon — which FCU?
Switched FCU: the default choice — lets you isolate the appliance for cleaning or service without touching the consumer unit. Neon indicator: worth the small premium wherever the appliance is out of sight (airing-cupboard boilers, loft fans) — the neon confirms power at a glance. Unswitched FCU: for circuits that must not be switched off accidentally, such as alarm panels and smoke detection. Flex outlet versions give the tidiest finish where the appliance cable runs straight out of the wall.
Frequently asked questions
Can I replace a socket with a fused spur?
Yes — an FCU fits the same single back box and connects to the same ring or radial circuit. It's a common conversion when an appliance becomes a permanent fixture.
What fuse goes in a fused spur?
Match the appliance: 3A up to ~700W (clocks, alarms, extract fans), 5A up to ~1100W, 13A up to 3kW (towel rails, heaters). Never just leave the factory 13A fuse in for a small load.
Does a boiler need a fused spur?
Manufacturers almost universally require boilers on a switched 3A fused spur so the boiler can be isolated for service — check your MI, but a plug socket is rarely acceptable.
Can a fused spur feed a socket?
Yes — a 13A FCU can feed a single or double socket as a fused spur off the ring; the FCU's fuse then protects the spur cable.
Shop fused connection units
- All fused connection units — switched, unswitched, neon & flex outlet
- BG Nexus Metal FCUs — brushed steel, chrome, brass
- Custom engraved fused switches — labelled "BOILER", "FAN" etc.
- Cooker switches & sockets (45A) — for loads beyond 13A
Wiring it into a bathroom or wet area? Check the BS 7671 bathroom zones guide first. Trade volumes? Open a trade account.