CABLE CLEATS, CLAMPS & HANGERS
WHAT ARE CABLE CLEATS?
Cable cleats are used to fix, clamp and support cables – cleats provide effective short circuit protection, support and retention to LV, MV and HV power cable systems when installed at intervals to circuits to secure electrical installations.
The cable cleats provide restraint and prevent excessive cable movement resultant from fault-current magnetic forces – cleats must be suitably rated for cable size (outside diameter) and anticipated fault current (peak fault level kA).
Correctly specified cable cleats will withstand the forces corresponding to the values of the peak prospective short-circuit current.
Power cable system designers, engineers and specifiers must consider the correct cable fixing or securing system to provide safe and adequate restraint and protection of LV, MV or HV cables – cable cleats restrain movement of cables during electrical fault conditions.
Cable cleats are available to suit all environmental conditions (onshore and offshore), industrial applications and operating voltages – specialist cable fixings for fire resistant, low smoke zero halogen (LSF LSOH) and quadrafoil (Quad) cable installations.
CABLE CLEAT SPECIFICATION
Selection of cable cleats should consider several key factors:
Cable Diameter – the overall diameter of the LV-HV cable ensure the correct size of cleat is chosen. This dimension, namely the outside cable diameter around the cable sheath, is also required for calculating short circuit forces the cleat could potentially be subject to under fault conditions.
Performance – depending on the cable installation application there may be a requirement for the cleat to include material performance and specification features, for instance fire resistance, LSF (Low Smoke Fume), LSOH LSZH (Low Smoke Zero Halogen) or corrosion resistant (stainless steel)
Cable Type – check cable voltage and construction: LV Low Voltage, MV Medium Voltage or HV High Voltage.
Cable Cleats: this photo emphasizes the importance for cable cleats to restrain cables during a short circuit. The cleated portion of the cable remained securely fixed to the containment during the test, whereas the unrestrained portion of cable moved violently, with the potential to injure personnel in the area. This short circuit test was carried out in controlled conditions and the fault level was 174kA with 300mm cable cleat spacing. The Ellis Patents cable cleats were used in conjunction with Vantrunk Speedway cable ladder containment.
Other factors include cable type, ratings, power system design, cable management/containment structure and installation environment – complete ranges of single cable cleats, trefoil cable cleats, quad cleats or bespoke engineered and designed to specific application requirement.
Short Circuit Protection Using Cable Cleats
The following Video clearly demonstrates Ellis Emperor Cable Cleats clamping single core cables in trefoil arrangement being subjected to a short circuit fault condition with 118kA peak – the slow motion replay highlights the extreme physical force and strength generated by the short circuit as the cable cleats effectively restrain the power cables to the containment.
Cable cleats provide effective cable management of low, medium and high voltage power cables requiring short circuit protection.
CABLE CLEATS & CLAMPS
Flat, Trefoil & Quadrafoil Cables
Cable arrangements for 3 phase installations utilising single conductor cables are typically flat spaced, flat touching or trefoil.
In the UK the 17th Edition Wiring Regulations (BS7671) provides current ratings and voltage drop values for all these cable configurations – information is also available on grouping factors and spacing between circuits to achieve thermal independence.
Power systems with increased anticipated short circuit levels also expose installed cables to elevated temperatures (conductors can reach up to 250°C) – the high temperature leads to a softening of the cable insulation and outer cable sheath jacket exposing the cable to potential damage by the cleat. To counteract this cable cleats are available with polymeric liners.
Cable Expansion & Single Core Cables
Single core cables, operating at low, medium or high voltage, expand and contract under thermal cycling at higher levels than multicore cables – if the cable is constrained considerable forces can be transferred to the supporting structure. To allow for this, single core cables are generally “snaked” allowing slight loops to accept the cable expansion and contractor. It is also usual to allow some of the cable cleats to move freely and not restrain all cable cleats.
Cleating Trefoil & Triplex Cables
The cable liner surrounds are used to protect medium/high voltage power cables typically supplying electricity at 11kV – the cable cleat liners are surrounded as standard in a LSF Zero Halogen polymeric materials. The trefoil or Triplex surrounds are used with single cable cleats to secure Triplex cables (three single core cables spirally twisted together), overcoming the twist in the cable to be cleated at any point along the installed length.
Without cable surrounds the installation of cable cleats would be difficult due to the relative position of the Triplex cable being subject to variation along the cable run – here the inner liner is applied around the Triplex cables and then a standard cable cleat has been used. Note either polymeric or stainless steel cable cleats can be used depending on the short circuit ratings of the cable system.