Cable Cleats
Trefoil Cable Formation Explained
July 23rd, 2026
Trefoil cable formation is an installation method where three single core power cables are arranged together in a triangular, shamrock-style formation. Each cable normally represents one phase of a three-phase electrical circuit, and the three cables are held together using trefoil cable cleats or cable clamps.
Trefoil formation is commonly used for LV, MV and HV single core cable installations, including 600/1000V, 11kV, 33kV, 66kV and higher voltage power cable systems. It is used across substations, industrial power networks, renewable energy projects, data centres, utilities, rail infrastructure and electrical distribution systems.
The purpose of trefoil formation is not only neat cable management. It also helps manage magnetic effects, reduces cable spacing, supports short-circuit restraint and keeps the three phases correctly grouped along the cable route. When single core cables are installed in trefoil, they must be restrained with suitable cable cleats selected according to cable diameter, fault level, support structure, cleat spacing and project specification.
Thorne & Derrick supply trefoil cable cleats, LV MV HV cable cleats, Ellis Patents cleats, Prysmian BICON cleats and tested cable restraint systems for single, trefoil, quadrafoil and bundled power cable installations.
Quick Answer: What Is Trefoil Cable Formation?
Trefoil cable formation is the arrangement of three single core power cables in a triangular formation. The three cables normally represent the three phases of a three-phase circuit and are installed together using trefoil cable cleats.
Trefoil formation is commonly used for single core LV, MV and HV cables. It helps keep the phases grouped, reduces magnetic imbalance compared with widely spaced single cores, supports efficient cable installation and allows the cables to be restrained using tested cable cleats.
What Is Trefoil Cable Formation?
Trefoil cable formation is a method of installing three single core cables together so that the cable centres form a triangle. The term “trefoil” comes from the three-lobed shape created when the cables are grouped together.
In a three-phase circuit, the single core cables are usually arranged as:
- L1 / Phase A
- L2 / Phase B
- L3 / Phase C
The three phases are held together using a trefoil cable cleat. The cleat clamps around the three cables and fixes them to the cable ladder, tray, bracket, Unistrut, concrete surface or steelwork.
Trefoil formation is most common when the electrical design uses three single core cables instead of one multicore cable. This is often seen on larger power circuits where cable size, current rating, installation method, handling, bending radius or system design makes single core cables more practical.
Why Are Single Core Cables Installed In Trefoil?
Single core cables are installed in trefoil for several electrical and mechanical reasons.
The three phases of an AC circuit create magnetic fields around the cables. If single core cables are spaced too far apart or installed incorrectly, magnetic effects can increase losses, induce currents in nearby metallic components and create unwanted heating.
Trefoil formation helps keep the phases close together. This helps balance the magnetic fields produced by the three phase conductors and can reduce the risk of heating effects in nearby metalwork compared with poorly arranged single core cable routes.
Trefoil formation also helps:
- Keep the three phases grouped along the route
- Reduce the overall cable footprint
- Simplify cleating and restraint
- Improve cable route organisation
- Support short-circuit force restraint
- Maintain phase identification and circuit grouping
The exact formation should always follow the electrical design, cable manufacturer guidance and project specification.
Trefoil vs Flat Cable Formation
Single core cables are commonly installed in either trefoil formation or flat formation. Both methods can be correct, depending on the installation design.
Trefoil is often chosen where compact grouping and magnetic field balance are important. Flat formation may be used where the design needs greater cable spacing for thermal performance, specific route constraints or installation access.
Why Trefoil Cable Cleats Are Used
Trefoil cable cleats are used to clamp, support and restrain three single core cables installed in trefoil formation. They keep the cable group fixed to the support structure during normal service and during fault conditions.
Cable cleats are not just cable tidies. In power cable systems, they are safety-critical components. During a short circuit, very large electromagnetic forces can act between the cables. If the cleats are under-specified, poorly spaced or incorrectly installed, the cables may move violently and damage the installation.
Trefoil cable cleats help:
- Retain cables during short-circuit conditions
- Maintain phase grouping
- Support the cable weight
- Control cable movement
- Protect nearby equipment and structures
- Support compliance with project and standard requirements
Thorne & Derrick supply trefoil cable cleats for LV, MV and HV cable systems, including cleats for 11kV, 33kV and higher voltage applications.
Short-Circuit Forces & Cable Restraint
When a short circuit occurs, the current flowing through the cables can generate very high electromechanical forces. These forces can cause cables to move, twist, strike nearby equipment or break free from unsuitable supports.
The force depends on factors such as:
- Peak fault current
- Cable diameter
- Cable spacing
- Cable formation
- Cleat spacing
- Support structure strength
- Cable route changes and bends
This is why cable cleats should be selected using actual project fault data and cable dimensions. A cleat that physically fits the cable is not automatically suitable for the fault level.
For more detail, see the Power & Cables guide to IEC 61914 cable cleats and short-circuit protection.
IEC 61914 & Cable Cleat Testing
IEC 61914 is the international standard for cable cleats used in electrical installations. It covers important cable cleat performance requirements, including mechanical strength, short-circuit testing, impact, corrosion, UV resistance and other classification areas.
For trefoil cable installations, IEC 61914 is important because it helps prove that a cable cleat has been tested for the type of cable restraint duty it may face in service.
Cable cleat selection should consider:
- IEC 61914 classification
- Short-circuit test performance
- Peak withstand current
- Cleat material
- Cable diameter range
- Maximum recommended spacing
- Installation environment
- Support structure compatibility
Browse the Power & Cables cable cleats guide for more information about specification, types and standards.
Where Is Trefoil Formation Used?
Trefoil cable formation is used wherever three single core cables need to be installed as a three-phase power circuit.
Common applications include:
- LV power distribution – large single core 600/1000V cable circuits.
- 11kV and 33kV MV networks – substation, utility and industrial medium voltage cable routes.
- 66kV and 132kV HV circuits – transmission and grid infrastructure cable installations.
- Substations – transformer, switchgear and cable sealing end connections.
- Renewable energy projects – solar farms, wind farms, battery storage and grid connections.
- Data centres – high current power distribution and backup power circuits.
- Industrial sites – process plants, factories, utilities and large motors.
- Cable tunnels, trenches and risers – controlled cable support and containment routes.
Trefoil cleats may be installed onto ladder rack, cable tray, steelwork, concrete structures, Unistrut or dedicated support brackets depending on the route design.
How To Select Trefoil Cable Cleats
Selecting the correct trefoil cable cleat requires technical project information. The cleat must match the cable size, system duty and environment.
For detailed advice, see the complete range of cable cleats, clamps and hangers.
Common Trefoil Installation Mistakes
Trefoil cable installation mistakes can reduce safety, reliability and installation quality.
Common mistakes include:
- Using cable ties instead of tested cleats – cable ties are not suitable for restraining high short-circuit forces.
- Selecting cleats only by cable diameter – fault level and cleat spacing are also essential.
- Ignoring short-circuit forces – cables can move violently during fault conditions if not properly restrained.
- Incorrect cleat spacing – wide spacing may reduce restraint performance.
- Mixing cable phases incorrectly – the three phases should remain correctly grouped along the route.
- Poor support structure design – the ladder, tray or steelwork must be strong enough for the forces involved.
- Ignoring bend and route changes – bends and vertical runs may require closer cleating or additional support.
- Using unsuitable cleat materials – corrosion, UV, chemical or fire exposure can affect material choice.
- Not checking IEC 61914 test data – cleat performance should be proven, not assumed.
Correct trefoil installation is a combination of cable design, fault calculations, cleat selection, cleat spacing and good installation practice.
Related Trefoil Cable & Cable Cleat Products
Trefoil cable formation is part of a wider single core cable and cable cleat system.
- Trefoil Cable Cleats – cleats for retaining three single core cables in trefoil formation.
- Cable Cleats, Clamps & Hangers – cable restraint products for LV, MV and HV installations.
- Ellis Patents Trefoil Cable Cleats – trefoil cleats for cable restraint and short-circuit protection.
- Ellis Alpha Trefoil Cable Cleats – aluminium trefoil cable cleats for LV, MV and HV applications.
- Ellis Trident Cable Cleats – cable cleats for LV, MV and HV power cable systems in trefoil installation.
- Cable Cleats Guide – guide to cable cleat specification, types and standards.
- IEC 61914 Cable Cleats – guide to cable cleat short-circuit protection and IEC 61914.
- Single Core XLPE Cables – single core power cables commonly restrained in trefoil formation.
Trefoil Cable FAQs
Q: What is trefoil cable formation?
A: Trefoil cable formation is the arrangement of three single core power cables in a triangular formation. The three cables usually represent the three phases of a three-phase circuit and are restrained using trefoil cable cleats.
Q: Why are cables installed in trefoil?
A: Cables are installed in trefoil to group the three phases closely together, help manage magnetic effects, reduce cable route footprint and allow the cables to be restrained using tested trefoil cable cleats.
Q: What are trefoil cable cleats?
A: Trefoil cable cleats are cable clamps designed to hold three single core cables together in trefoil formation. They support the cable weight and help restrain the cables during short-circuit conditions.
Q: What is the difference between trefoil and flat formation?
A: Trefoil formation groups three single core cables in a triangular arrangement. Flat formation installs the three cables side by side in a row. The correct choice depends on current rating, cable spacing, fault level, thermal performance and route design.
Q: Are cable ties suitable for trefoil cables?
A: Cable ties are not suitable for restraining high short-circuit forces in power cable installations. Trefoil cable cleats should be selected using cable diameter, fault current, cleat spacing and tested performance data.
Q: What is IEC 61914?
A: IEC 61914 is the international standard for cable cleats used in electrical installations. It covers performance requirements including mechanical strength, short-circuit testing, impact, corrosion and environmental classification.
Q: How do you choose trefoil cable cleat spacing?
A: Trefoil cable cleat spacing should be based on cable diameter, fault current, cable route, cleat test data, support structure and manufacturer guidance. It should not be guessed or based only on visual cable support.
Q: Where is trefoil cable formation used?
A: Trefoil cable formation is used in LV, MV and HV power cable systems, including substations, cable tunnels, ladders, trays, risers, utilities, renewables, data centres and industrial power networks.
Conclusion
Trefoil cable formation is a common method for installing three single core power cables in a three-phase circuit. The cables are arranged in a triangular formation and restrained using trefoil cable cleats.
Trefoil formation helps keep the phases grouped, supports magnetic field balance, reduces cable route footprint and allows the cables to be restrained against short-circuit forces. Correct cleat selection is essential, especially for LV, MV and HV power systems where fault levels can be high.
Trefoil cable cleats should be selected using cable diameter, formation, short-circuit current, cleat spacing, installation environment, support structure and IEC 61914 test data.
Thorne & Derrick supply trefoil cable cleats, cable clamps and cable cleat systems for LV, MV, HV and EHV power cable installations, including Ellis Patents, Prysmian BICON and other tested cable restraint solutions.
Are Your Cable Cleats Fit for Data Centres? Rethinking High-Density Cable Management
April 10th, 2026
Rethinking Cable Cleats for High-Density Data Centres
Global demand for cloud computing, AI workloads and digital services is accelerating the construction of data centres at an unprecedented scale. Hyperscale facilities are now being developed across Europe, North America and Asia, placing increasing pressure on electrical infrastructure.
Inside these environments, power distribution systems are becoming larger, denser and more complex. Electrical energy must move efficiently from substations to switchgear, generators, UPS systems and distribution panels through extensive networks of large single-core power cables.
These cables carry significant electrical loads and must be properly restrained using Band-IT manufactured cable cleats as part of safe and effective data centre cable management.
Why Cable Cleats Matter More Than Ever
In modern data centres, cable routing is no longer straightforward. High-density tray systems, parallel feeder arrangements and evolving layouts create increasingly complex installation environments.
As outlined in our guide to cable cleats, these devices are specifically designed to secure and restrain power cables, particularly during short-circuit events where mechanical forces can be extreme.
Without proper restraint, cables can shift or whip under magnetic forces, risking damage to insulation, equipment and power continuity.
The Installation Challenges Behind Traditional Cable Cleats – Installation Friction
Traditional cable cleats are often installed before cable pulling begins. This requires installers to pre-stage hardware and predict exact cleat locations in advance.
In practice, this approach introduces several issues:
- Cleats can interfere with cable rollers, increasing friction during pulling
- Parallel feeder installations become more difficult in dense tray systems
- Installers must work around heavy cables in confined spaces after pulling
- Multi-component systems increase handling time and installation errors
In high-density environments, these challenges can significantly slow down installation.
Engineering Complexity
Many traditional systems require multiple cleat sizes such as single way cable cleats to match different cable diameters and configurations. :contentReference[oaicite:1]{index=1}
This creates additional work for engineering teams, including spacing calculations, SKU selection and adapting designs as routing evolves.
Project Impact
What appears to be a minor component can have a wider impact across the project:
- Increased material costs
- Extended installation time
- Programme delays from rework or inefficiencies
Why Cable Cleats Are Critical for Electrical Safety
Cable restraint is essential for maintaining safety under fault conditions.
During a short-circuit event, extremely high currents generate powerful magnetic forces between conductors. These forces occur rapidly and can cause uncontrolled cable movement if not properly restrained.
Cable cleats are specifically designed to prevent excessive movement caused by fault-current magnetic forces, helping protect both equipment and personnel.
To ensure performance, cleats should comply with international standards such as IEC 61914, which defines testing requirements for short-circuit restraint capability.
WHAT TO LOOK FOR
- Short-circuit restraint capability
- IEC 61914 compliance
- Mechanical strength under electromechanical forces
- Suitability for high-density and high voltage installations
How Cable Cleat Requirements Are Changing in Data Centres
In high-density data centres, cable cleat selection is no longer based on performance alone. Engineers must now balance:
- Electrical performance
- Physical integration
- Installation practicality
As explored in our article on cable cleats in data centres, these systems are essential for maintaining safety, airflow and operational efficiency in modern facilities.
Post-pull installation methods are increasingly preferred, helping reduce friction during cable pulls and improving installer access in dense tray environments.
A Simpler Approach to Cable Cleats
Modern data centre projects require solutions that simplify both engineering and installation while maintaining compliance.
One approach is the use of post-pull cable cleat systems, designed to improve installation efficiency and reduce complexity.
Key Benefits
- Reduced obstruction during cable pulling
- Improved access in confined tray systems
- Lower SKU requirements
- Faster installation across large projects
High-performance solutions such as stainless steel or aluminium cable cleats are often specified depending on environmental conditions, corrosion resistance and required short-circuit ratings.
Why Installation Speed Is Now Critical
Modern data centre construction is driven by tight schedules, labour constraints and supply chain pressures.
In this environment, even small improvements in installation efficiency can deliver significant benefits. Where thousands of cleats are required, reducing installation time per unit can result in substantial labour savings.
Efficient cable cleat solutions can help maintain project timelines while supporting low voltage and high voltage electrical safety and compliance.
Choosing the Right Cable Cleat: A Practical Guide (IEC 61914 + Installation Tips)
February 23rd, 2026
Selecting the right cable cleat is a key part of designing and installing a reliable power distribution system. In environments such as industrial facilities, critical power and other electrical installations, cable cleats help ensure a short-circuit event does not escalate into major cable or equipment damage.
During a fault, electromagnetic forces rise rapidly and can cause cables to move violently. Correctly selected and installed cleats restrain cables during these brief but critical moments — supporting safety, equipment protection and overall system integrity.
This guide sets out practical steps to support cable cleat selection: understanding fault forces, the variables that influence cleat performance, and how to choose solutions that suit your cable formation, tray/ladder geometry and site constraints.
Practical rule of thumb
Cable cleats aren’t just tidy cable management. They are a mechanical safety component designed to restrain cables during short-circuit conditions.
Start with prospective fault level and formation, then work outwards to spacing, mounting geometry and installation constraints.
Specify BAND-IT Cable Cleats with Confidence
Tell us your cable sizes, formation, tray/ladder type and prospective fault level. We’ll help you identify a compliant, practical cable cleat solution for your installation.
Selection Support • Standards-Led Guidance • Project-Ready Supply
Ellis Patents Cable Cleats for Major Power Plant Project
May 27th, 2025
21.5.2025
HOLDING POWER by Ellis Patents | 30,000+ Vulcan Cleats and Flexistraps shipped out today under the blazing Yorkshire sun. The cable cleats will provide short-circuit restraint to both 11kV and 33kV Medium Voltage Cable Networks.
This WIN demonstrates the high-value of collaborative, proactive and strategized Manufacturer-Distributor relationships; we look forward to co-creating a Case Study to highlight how together we have worked to secure this achievement and satisfy clients specification and technical application requirements.
The consignment is now to be delivered to SEB International Ltd, the UK’s leading manufacturer of Cable Pulling & Laying Equipment, and consolidated for shipment with a CD500S Cable Drum Trailer (Payload 20,000kgs | Max Drum Width 2400mm), TW5000 Cable Pulling Winch and CP700 Cable Pushing Unit to power-up an accelerated cable laying process.
The £750K project value to Thorne & Derrick demonstrates our ability to manage and deliver upon UK and international major projects from our robust world-class supply-chain.
The High Voltage 132kV Cables will be connected to Grid using GIS Dry-Type Terminations from Nexans while all Medium Voltage 33/11kV switchgear and transformer Connectors are completed using market-leading Euromold and Connex brands from Nexans Power Accessories and Pfisterer.
All Cleats & Cable Accessories supplied by Thorne & Derrick – the purchase contract was managed by Gary Amos (Thorne & Derrick Sales Engineer).
Ellis Patents | HOLDING POWER
Pictured | Carl Cox (Thorne & Derrick Sales Engineer | Rail) with Noman Shabir (Ellis Patents National Sales Manager). The Ellis Patents ranges of PADS Approved Cable Cleats & Tunnel Hangers provide advanced material performance for substation, trackside and tunnel applications; this includes the short-circuit restraint and support of LV MV HV power cables. Please do not hesitate to contact Thorne & Derrick should you require further info, Lunch n Learn, CPD or Joint Visit to discuss your next cable cleat project requirements.
Ellis Patents Emperor Cable Cleats | Single & Trefoil | cable cleats designed, developed, tested and manufactured by Ellis from the Emperor range in accordance with IEC 61914 suitable for single, trefoil and Quad cable configurations
Ellis Patents Centaur Cable Saddles | the Ellis Centaur cable cleat has been designed, developed, tested and manufactured in accordance with IEC 61914 (Cable Cleats for Electrical Installations). The cable saddles are designed to support High Voltage Power Cables with diameters from 100mm to 162mm. Centaur consists of an extruded and pressed aluminium saddle and a hinged aluminium over strap.
Ellis Patents Aluminium Cable Cleats | the Ellis 2A two hole cable clamps have been designed, developed, tested and manufactured in accordance with IEC 61914 (Cable Cleats for Electrical Installations). The cable clamps are available in a range of sizes with range taking ability to suit single cables – the clamp can be epoxy coated for use in harsh environments, such as sea air conditions.
Ellis Patents Vulcan Cable Cleats | the Vulcan cleats are available in a range of sizes with range taking ability to suit single and trefoil cable formations (also available in Quad formation). The frame of the cleat is manufactured from corrosion-resistant 316L grade stainless steel, the cable is supported by a liner manufactured from a low smoke zero halogen (LSOH) material.
Ellis Patents Colossus Cable Cleats | The Colossus cleat is available in a range of sizes with range taking ability to suit LV MV HV cables in trefoil formation. The frame of the cleat is manufactured from grade 316L stainless steel, and the body of the cable cleat is manufactured from a low smoke and zero halogen (LSOH) material.
Ellis Patents Trident Cable Cleats | cable cleat is available in a range of sizes with range taking ability to suit LV MV HV cables in trefoil formation. The cleat is manufactured as standard in LSF which is PFAS and halogen free, flame retardant and suitable for outdoor applications.
Further Reading
- Ellis Patents Extend Vulcan+ Cable Cleat Range To Accommodate Smaller Cables
- Polymer Cable Cleats | Holding Power with Ellis Patents
- Cable Cleats | A Device For Short Circuit Protection | CPD Course By Ellis Patents
Understanding The Critical Role Of Cable Cleats in Data Centres
March 31st, 2025
Do You Need Cable Cleats in Data Centres?
In an increasingly digital world, Cable Cleats in Data Centres are crucial in support of the backbone of global connectivity. Every click, transaction, and streamed video relies on complex Data Centre infrastructures operating seamlessly. As the demand for high-speed data and reliable uptime continues to grow, so too does the need for robust electrical infrastructure. Among the often-overlooked yet crucial components of Data Centre design is cable management – ensuring that LV MV HV Power Cables and data cables are installed, protected, and maintained to the highest standards.
What is a Cable Cleat?
Cable Cleats are devices used to secure, fix, strap and support electrical power cables in an installation, ensuring safe operation and prevention of damage or injury, specifically in the event of a short circuit. Cable Cleats in Data Centres are ultimately purposed to increase/enhanced safety, organisation, cable protection, containment and ensure optimal performance. Typically, Cable Cleats are designed to be attached to various surfaces, such as ladders, trays, struts, rails, or beams.
LV MV HV Power Cable Management in Data Centres
Modern data centres are high-density environments where vast amounts of power are distributed through extensive cabling systems. These installations face several key challenges:
- High Power Demand: Data Centres require vast amounts of electrical power, leading to high-capacity cabling systems that must be properly supported and secured.
- Thermal Management: Poor cable management with no Cable Cleat usage can obstruct airflow, leading to overheating and reduced efficiency.
- Fire Safety: Electrical faults, if not properly contained, can pose a serious risk to critical infrastructure and personnel. Regulations require secure cable installation to prevent short circuits and mitigate fire hazards.
- Maintenance and Upgrades: Well-organised cabling simplifies maintenance and reduces downtime as data centres are continually evolving.
Cable Cleats Critical Role in Ensuring Safety and Performance
Cable Cleats, Clamps & Hangers play a fundamental role in securing electrical power cables, particularly in high-voltage environments. While they may be a small component of the overall electrical system, their importance cannot be overstated. Cable Cleats in Data Centres provide vital protection by:
- Protection during Short Circuits and Electrical Failures: In the event of a fault, the forces generated by high-powered electrical cables can be immense. Without proper restraint, power cables can move violently, leading to catastrophic failures. Cable Cleats hold cables in place, mitigating these risks.
- Ensuring Compliance with Industry Standards: International regulations, such as IEC 61914 Power Cable Standards, set stringent requirements for cable fixing and restraint systems. High-quality cable cleats ensure compliance with these safety standards.
- Aiding Thermal Management: Securely spaced cables allow for improved airflow and more efficient heat dissipation, contributing to the overall energy efficiency of a Data Centre.
- Enhancing Longevity and Reliability: Properly restrained cables experience less wear and tear over time, reducing the likelihood of maintenance issues and unplanned outages.
How Do You Choose the Right Cable Cleats for Data Centres?
Not all Cable Cleats are created equal, and selecting the right product for a Data Centre environment requires careful consideration to provide optimal LV MV HV power cable support. Key factors include:
- Performance Under Fault Conditions: Cleats must be tested under high short-circuit conditions to ensure they provide adequate restraint in the event of a fault.
- Material Selection: Corrosion-resistant materials such as stainless steel or high-strength polymers are ideal for ensuring longevity.
- Installation Flexibility: Data centres often require custom cable arrangements, so cleats should allow for easy installation and adaptability to different configurations.
Cable Cleats, Clamps & Hangers
Cable Cleats in Data Centres aren’t necessarily the most visible component. However, Cable Cleats, Clamps & Hangers play an indispensable role in securing the power supply that keeps the digital world running from Data Centres. A well-designed support system incorporating compatible Cable Cleats protects infrastructure while contributing to operational efficiency and regulatory compliance.
Cable Clamps | Single & 2 Hole Clamps | Aluminium & Plastic | No-Bolts Cleats Stackable & Boltless LU Approved
Thorne & Derrick are stockists and suppliers of a complete range of Cable Cleats used to clamp and retain low, medium and high voltage cables in the event of a short circuit, including 11kV/33kV MV HV power cables – single-way cable cleats, trefoil cable cleats, quadrofoil cable cleats, emperor cable cleats and multiple bundled cable configurations can be cleated using Ellis Patents and Prysmian manufactured Cable Cleats in a choice of materials including nylon, stainless steel and aluminium.
