Fused Connection Units (FCUs), commonly known as fused spurs, are widely used in UK electrical installations alongside socket outlets. They provide a safe and controlled way to supply fixed appliances from a socket circuit while offering additional protection through an integrated fuse.

FCU usage and installation are guided by BS 7671 standards issued by BSI.

What Is an FCU?

An FCU is a device that contains a replaceable fuse, typically rated at 3A or 13A, and is used to connect an appliance directly to the electrical supply. It can be connected to a ring final circuit or radial circuit.

Unlike a standard socket outlet, an FCU is usually hardwired to an appliance rather than using a plug.

How FCUs Work

The main function of an FCU is to provide local protection for the connected appliance. The fuse inside the FCU protects the appliance cable and internal components from overcurrent.

For example:

• A boiler may require a 3A fuse
• A water heater may require a 13A fuse

The correct fuse rating must always be selected based on the appliance specifications.

Types of FCUs

There are two common types of FCUs:

Switched FCU
Includes a switch to isolate the appliance. This is commonly used for boilers, heaters, and kitchen appliances.

Unswitched FCU
Does not include a switch and is used where isolation is not required or is provided elsewhere.

Some FCUs also include neon indicators to show when power is on.

Applications in UK Installations

FCUs are commonly used for:

• Boilers and central heating systems
• Extractor fans
• Dishwashers and washing machines
• Outdoor equipment
• Fixed lighting circuits

They are especially useful where an appliance needs to be permanently connected but still requires fuse protection.

FCUs and Spurs

FCUs are often used as fused spurs from a ring circuit. A fused spur allows multiple outlets or a fixed appliance to be connected safely without overloading the circuit.

Without a fuse, an unfused spur is limited to supplying only one socket.

Installation Considerations

Electricians must ensure:

• Correct fuse rating is installed
• Proper cable termination
• Adequate mounting and accessibility
• Correct polarity and earthing

FCUs should also be positioned in accessible locations for maintenance and fuse replacement.

Safety Benefits

FCUs provide several important safety advantages:

• Localised overcurrent protection
• Safe isolation of appliances
• Reduced risk of cable overheating
• Controlled load connection to circuits

They are particularly useful for appliances that operate continuously or are not easily unplugged.

Conclusion

Fused Connection Units are an essential part of UK electrical installations. They provide safe and flexible connections for fixed appliances while ensuring proper protection through fuse control.

For electricians, correct selection and installation of FCUs improve both safety and system reliability.