A fused connection unit (FCU) is an electrical outlet or spur point that combines a fuse with a means of connecting a fixed appliance or a separate circuit. It is commonly used in homes and buildings to safely supply power to items like water heaters, boilers, extractor fans, or lighting circuits.

Its main purpose is protection. The fuse inside the unit is a safety device designed to melt and break the circuit if too much current flows through it. This helps prevent overheating, damage to equipment, and electrical fires. The fuse is usually rated to suit the appliance being supplied, often 3A, 5A, or 13A.

An FCU works by taking power from the main circuit and passing it through the fuse before it reaches the connected appliance or outlet. If the appliance operates normally, electricity flows through as usual. If a fault occurs, such as a short circuit or overload, the current rises above the fuse rating. The fuse then blows, interrupting the flow of electricity and isolating the faulty circuit.

Many fused connection units also include a switch, allowing the appliance to be turned on or off without removing the fuse. Some are switched, some unswitched. They may also be used as a safe way to connect a spur from a ring main circuit.

In simple terms, a fused connection unit is a protective electrical connection point that supplies power while guarding against excessive current.

Use a fused connection unit (FCU) instead of a socket when you want to permanently or semi-permanently power an appliance from a fixed circuit, especially if that appliance needs a lower-rated fuse than the circuit provides.

Typical cases include:

• Boilers
• Hardwired heaters
• Extractor fans
• Dishwashers or fridges in some installations
• Other appliances that are not meant to be unplugged regularly

An FCU is useful when:

• The appliance should not be casually disconnected
• You want local isolation for maintenance
• The appliance needs protection from a fuse smaller than the main circuit breaker
• You want a cleaner, safer fixed installation than a normal plug-and-socket arrangement

Use a socket instead when the appliance is intended to be plugged in and moved or replaced easily, such as lamps, chargers, TVs, or most portable equipment. A socket is usually better for appliances that may need frequent access, testing, or replacement.

In short: choose an FCU for fixed appliances and controlled protection; choose a socket for portable, user-pluggable devices.

If you are unsure, the appliance’s instructions and local wiring rules should decide it, and an electrician should confirm the correct arrangement.

Use the lowest fuse rating that safely matches the appliance and cable it protects.

In a fused connection unit (FCU), the fuse is chosen to protect the flex/appliance, not just to “match” the load. In the UK, the common fuse ratings are 3A, 5A, and 13A:

3A: For low-power loads and most lighting circuits, boilers, and small fixed appliances.

5A: For moderate loads where the manufacturer specifies it or where 3A is too small.

13A: For higher-power appliances up to the limits of a standard plug/fused spur, but only if the connected cable and appliance are designed for it.

As a rule: Use the appliance manufacturer’s stated fuse rating if given. If not, choose the smallest fuse that will not blow during normal operation. Never fit a larger fuse “just to stop it blowing,” because that can leave the cable unprotected and create a fire risk.

If you are unsure, check: The appliance rating label The cable size The manufacturer instructions Local wiring regulations

For many fixed appliances, 3A is often sufficient. For anything involving heating elements, motors, or uncertain load characteristics, get the specification confirmed by a qualified electrician.

If you want, I can also give you a quick table of common appliances and recommended FCU fuse sizes.

Yes. A fused connection unit can be either switched or unswitched, depending on its design and purpose.

A switched fused connection unit has an integral switch, so it can isolate and control the appliance or circuit it feeds. This is useful for fixed appliances such as water heaters, boilers, extractors, or fridges, where you may want local on/off control and safe isolation for maintenance.

An unswitched fused connection unit has no switch. It provides a permanent connection through the fuse only, so the circuit remains live unless isolated elsewhere, usually at the consumer unit or another upstream isolator. This type is often used where local switching is not needed.

Both types contain a fuse to protect the connected appliance or cable from overload or fault current. The main difference is simply whether the unit also includes a switch.

So, in short: yes, a fused connection unit can be switched or unswitched, and the choice depends on whether local isolation/control is required.

A fused connection unit (FCU) is wired to provide a local switch and a replaceable fuse for a fixed appliance. Before starting, isolate the circuit at the consumer unit, verify dead with a tester, and follow local wiring regulations. If unsure, use a qualified electrician.

Typical wiring is as follows: the supply live conductor goes to the terminal marked L IN or COM; the supply neutral goes to N IN; and the earth conductor goes to the earth terminal. If the FCU is feeding a single appliance, the outgoing live from L OUT goes to the appliance’s live, and the outgoing neutral from N OUT goes to the appliance’s neutral. The earth is continuous to the appliance and metal back box if fitted. In some FCUs, only the supply side and load side are marked L and N, so match in and out accordingly.

Choose the correct fuse rating for the load, commonly 3A for small loads or 13A for heavier approved loads, but always size it to the appliance and cable. Use the correct cable size and ensure all conductor ends are stripped neatly and fully tightened in the terminals. No bare copper should be exposed outside the terminals.

To install, mount the back box securely, route the cables safely, connect the conductors, fit the fuse, and secure the front plate. Restore power and test operation, polarity, and earth continuity. Ensure the switch and fuse rating match the intended appliance.