Fitting a fused spur involves more than mounting a fused connection unit on the wall. The existing circuit must first be identified and assessed, the circuit made safely dead, the correct FCU and cable arrangement selected, the accessory installed to its manufacturer’s instructions, and the completed alteration inspected and electrically tested before it is put into service.
A fused spur is fixed mains electrical work.
The process below explains how a competent installer approaches the job rather than providing a terminal-by-terminal DIY wiring instruction. A diagram cannot confirm whether an existing ring, radial circuit, protective device, earthing arrangement or cable route is suitable for alteration.
Key Takeaways
- Identify the existing circuit before deciding where the fused spur will be supplied from.
- Safe isolation and proving the circuit dead come before opening or altering fixed wiring.
- The FCU must suit the intended load, circuit arrangement and manufacturer’s connection requirements.
- The fuse in the FCU should suit the connected equipment rather than automatically being 13 A.
- The alteration needs inspection and electrical testing after installation.
What Needs Checking Before a Fused Spur Is Fitted?
The first job is to establish what the existing electrical circuit actually is. An accessory being close to a socket does not automatically mean it is suitable to supply another connection.
The installer needs to consider the circuit arrangement, conductor sizes, protective device, earthing, RCD protection where applicable, existing loading and the condition of the wiring. The intended equipment also matters because an FCU supplying a small fixed load presents a different design question from adding another general-purpose electrical point.
The location should be planned before the wall or existing accessory is disturbed. Cable routes, accessibility, mechanical protection and the position of the equipment being supplied all affect the installation.
How Is a Fused Spur Fitted Properly?
A competent installation normally follows a sequence of assessment, isolation, installation and verification. The exact connection arrangement depends on the existing circuit and the particular fused connection unit being installed.
Identify the Existing Circuit
Confirm which circuit supplies the proposed connection point and establish whether it is a ring, radial or another arrangement before altering it.
Assess the Proposed Load
Check what the FCU will supply, the equipment rating, cable requirements and the protective arrangements needed for the proposed load.
Safely Isolate the Circuit
The relevant supply is isolated and secured against accidental re-energisation, then the conductors are proved dead before fixed wiring is handled.
Prepare the Position and Cable Route
The accessory box and cable route are prepared so the new wiring can be installed without damaging existing cables or creating an unsuitable concealed route.
Install the FCU
Conductors are prepared and terminated to the markings and instructions for the actual accessory, while maintaining the required protective-earth continuity and secure connections.
Fit the Correct Fuse
A suitable BS 1362 fuse is selected for the downstream equipment and connection arrangement rather than simply fitting the highest available fuse rating.
Inspect and Test the Alteration
Relevant electrical tests are completed to verify that the modified circuit and protective measures remain suitable before the supply is restored for normal use.
Complete the Relevant Record
The documentation depends on the scope of the work. An alteration to an existing circuit and provision of an entirely new circuit are not the same certification situation.
Safe isolation is more than switching an appliance or wall switch off. Electrical Safety First’s professional guidance stresses preventing inadvertent re-energisation and keeping the point of isolation under effective control while work is carried out.
Where Can You Take a Supply for a Fused Spur From?
The supply point depends on the existing circuit design. It may involve an existing final circuit, but the arrangement has to be assessed rather than chosen from appearance alone.
Ring-final and radial circuits have different characteristics, and the presence of multiple cables at a socket does not by itself confirm what those cables do. Previous alterations may also mean that an accessory no longer forms part of the circuit in the way somebody expects.
If the proposed arrangement involves taking a further connection from an existing FCU, the narrower article
How to Fit a Fused Spur from a Fused Spur
covers that specific circuit question.
For a more detailed explanation of supply-side and load-side FCU arrangements, the separate
Fused Spur Socket Wiring & Installation
guide covers the wiring concept without turning this installation article into a duplicate wiring guide.
What Type of Fused Connection Unit Should Be Used?
Fused connection units are available in switched and unswitched forms. BS 1363-4:2023 is the current British Standard covering 13 A fused fixed connection units for household, commercial and light-industrial applications.
A switched FCU provides local switching as well as the fuse. An unswitched FCU retains the fused connection but does not have the same front-operated switching function. Which arrangement is appropriate depends on the connected equipment, required isolation arrangements and the overall design.
The accessory should also be suitable for the mounting method and environment. Manufacturer instructions remain important because terminal positions and connection details are not necessarily identical between products.
What Fuse Should Go in a Fused Spur?
The correct fuse depends on what the fused connection unit is protecting. A 13 A FCU can accommodate a BS 1362 fuse, but that does not mean every connected appliance should automatically be protected by a 13 A fuse.
Equipment manufacturers may specify the required protective fuse or electrical supply. The connected equipment, flexible cable where present and installation design all need to be considered before the fuse rating is selected.
Electrical Safety First similarly advises checking manufacturer instructions when choosing a BS 1362 fuse rather than assuming the largest rating is appropriate.
Does a New Fused Spur Need RCD Protection?
The FCU's fuse and RCD protection perform different functions. Installing a fused connection unit does not create RCD protection for the circuit.
The requirement for additional protection depends on the installation circumstances, including the circuit, wiring method, cable route, location and equipment being supplied. Any addition or alteration needs to be assessed against the requirements applying to the new work.
An older installation also should not automatically be declared unsafe simply because it was designed to an earlier edition of BS 7671. The IET notes that standards are not retrospective, although new alterations still need to be compatible with the existing installation and meet the applicable requirements for that work.
What Testing Is Required After Fitting a Fused Spur?
The new accessory should not simply be energised because it looks correctly connected. Inspection and testing are needed to verify the alteration and the protective measures associated with the affected circuit.
The appropriate tests depend on what has been changed. They can include checks relevant to protective-conductor continuity, insulation, polarity, fault protection and the operation of protective devices.
Testing also helps expose problems that are not visible from the front of the accessory, such as an incorrect circuit assumption or an existing defect that affects the safety of the alteration.
Is Fitting a Fused Spur Notifiable Under Part P?
In England, fitting an FCU is not automatically notifiable simply because fixed wiring has been altered. The notification position depends on the scope and location of the electrical work.
Current IET guidance on Part P states that installing a new circuit, replacing a consumer unit, or adding to or altering an existing circuit in a special location is notifiable. Other additions and alterations to existing installations outside special locations are generally non-notifiable.
Non-notifiable does not mean exempt from electrical-safety requirements.
Approved Document P still addresses the design, installation, inspection, testing and provision of information for electrical work in dwellings in England.
Part P is also an England-specific Building Regulations context. Requirements elsewhere in the UK should not be assumed to be identical.
Do You Need a Certificate After Fitting a Fused Spur?
The paperwork depends on the electrical work actually completed. The IET's current BS 7671 model Minor Electrical Installation Works Certificate is specifically intended for minor work that does not include the provision of a new circuit.
If the work forms part of an addition or alteration to an existing circuit, a Minor Electrical Installation Works Certificate may therefore be the relevant electrical record. If a completely new circuit has been installed, the certification requirement is different.
Where certification becomes the main question rather than the FCU installation itself, the
electrical installation certification
service explains certification for qualifying new electrical work.
Can You Fit a Fused Spur Yourself?
The physical accessory is only one part of the job. A safe alteration depends on identifying the circuit correctly, isolating it properly, selecting a suitable arrangement, making sound connections and carrying out the necessary electrical tests afterwards.
Electrical Safety First advises householders to leave electrical work to competent professionals rather than relying on online DIY instructions. If your main question is specifically whether you should attempt this work yourself, that decision is covered separately in
Can I Install a Fused Spur Myself?.
Keeping the subjects separate is useful: this article explains the professional installation process, while the DIY article covers the competence and legal boundary.
When Should the Existing Circuit Be Checked Before Installation?
Further investigation is sensible if there is uncertainty about the circuit arrangement, signs of previous alterations, damaged accessories, repeated tripping, overheating, discolouration, loose connections or unreliable power on the proposed supply circuit.
Adding another accessory does not correct an existing wiring fault. Where the condition of the circuit is unclear, it is better to
have the circuit tested
before the planned alteration proceeds.
What Has Changed in BS 7671 in 2026?
BS 7671:2018+A4:2026, the current Amendment 4 edition of the IET Wiring Regulations, was published on 15 April 2026.
There is a six-month transition period. The IET confirms that BS 7671:2018+A2:2022+A3:2024 remains a valid standard until 15 October 2026. During the transition, electrical installers may work to either edition; after that date Amendment 4 becomes the applicable current edition.
This standards transition does not by itself mean that every existing FCU or older electrical installation needs replacement. The condition and suitability of the existing installation and the requirements applicable to new work still need to be considered separately.
References & Standards
Technical and regulatory information was checked against current official guidance available on 21 August 2026.
Need a Fused Spur Installed?
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