What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
No local equivalentfused spur
also FCU, fused connection unit, switched spur, flex outlet
Exists because a ring final circuit is protected at 32 A while an appliance flex is not. A SPUR strictly means a branch off a ring; the fuse and the spur are separate ideas commonly named together.
Australia
No local equivalentfused connection unit
also appliance outlet, switched fused outlet
Radial circuits at lower protection levels mean the component is uncommon; a fixed appliance is normally supplied from its own appropriately rated circuit instead.
United Statesyours
No local equivalent(no direct equivalent)
also junction box, appliance disconnect, hard-wired connection
A branch circuit is protected at 15 or 20 A, which the appliance cord survives, so no intermediate fuse is required. Where local protection is needed the appliance carries it internally.
Canada
No local equivalent(no direct equivalent)
also junction box, disconnect means
As the United States, with a local disconnect required for some fixed appliances — which is about isolation for maintenance rather than about protecting a flex.
The governing standard, by market
United Kingdom
BS 1363-4 / BS 7671
Fused connection units as part of the 13 A plug and socket system, and the wiring regulations governing spurs off a final circuit.
United States
NFPA 70 (NEC) Article 422
Appliances: branch circuit sizing, disconnecting means, and the conditions for permanent connection.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Why does Britain need a component nobody else does?
- Because the ring final circuit protects the cable in the wall at 32 A, which is far more than anything plugged into it can survive. On a portable appliance the plug carries the fuse and solves it. On a FIXED appliance — an extractor fan, a boiler, a towel rail, an outdoor light, a waste disposal — there is no plug, so without something in between the appliance's flex is connected directly to 32 A of available protection. The fused connection unit is that something: a fixed accessory with a cartridge fuse rated for the appliance, and usually a switch so the appliance can be isolated. An American branch circuit protected at 15 or 20 A does not create the gap, so the component never had to be invented.
- What is a spur, and how many are allowed?
- A spur is a branch taken off a ring rather than part of the loop itself, and the rules exist because a spur is the one part of a ring not protected by having two paths. A single unfused spur may supply one single or one double socket, or one fixed appliance, and it is taken from a socket on the ring or from a junction box in it — the reasoning being that the spur cable carries only what that one point draws, not the whole ring's load. Anything beyond that goes through a FUSED spur, which drops the protection to the fuse rating and so allows a much smaller cable and more outlets beyond it. The common domestic error is extending a spur with a second socket, which puts two outlets on a cable protected at 32 A with no second path.
- Switched or unswitched, and does the fuse rating matter?
- Both are choices with consequences. SWITCHED lets the appliance be isolated locally, which is what makes it safe to work on a boiler or a fan without going to the consumer unit, and it is why a switched unit is normal for anything that will ever need servicing. UNSWITCHED is used where nobody should casually turn the appliance off — a freezer, an alarm, a trickle-charging circuit — and the switch would be a hazard rather than a convenience. The FUSE rating is chosen for the appliance and its flex, not for convenience: 3 A for small loads, 13 A for heating loads, and fitting 13 A everywhere because it is what came in the box removes the protection the unit exists to provide.