08. What is the recommended spacing between cable cleats?
Lineal cable cleat spacing decisions are based on the dynamic electromechanical forces between cables, cable deflection, axial retention (i.e. strain relief) requirements and the geometry of the cable support system. Talon Products is pleased to assist with cable force calculations utilizing our proprietary software. The results of the force calculations will allow customers to choose a lineal spacing that fits their unique application.
CAUTION: Some cable cleat spacing charts may only consider the results of the IEC 61914 static cable cleat lateral resistance test, which (in the case of non-rigid cable restraint designs) may include severe cable cleat deformation. Others may be based on an extrapolated force calculation that is erroneously based on the RMS or peak current magnitude in only one conductor (see FAQ-7). Some spacing charts may similarly disregard dynamic cable cleat strength and other critical factors such as cable protection, cable deflection, strain relief requirements and potential damage to the cable support system. During short circuit conditions, cable cleats are subjected to alternating attractive and repulsive forces between conductors. Therefore, cable cleats must be designed and tested to withstand multiple applications of dynamic force during an extremely short time period; not just a single static lateral pull test.
HORIZONTAL (i.e. side-by-side) SPACING
Horizontal cable cleat spacing decisions are based on cable ampacity requirements, spacing between the cables and the width and load distribution of the cable support system. National wiring standards like the (US) National Electrical Code provide cable ampacity tables that account for the mutual heating between conductors. For example, in order to achieve the published ampacity without thermal cable damage, trefoil cable bundles are separated from adjacent conductors with a free airspace of 2 to 2.15 times the cable diameter of the largest cable. With their patented rigid cable cleat design that simultaneously encloses cables and a support rung, Talon® T3 cable cleats installed side-by-side will comply with this spacing factor for cable diameters greater than ∅31 mm (1.22 in). For smaller cables or lower spacing factors, the cable cleats may be staggered on adjacent rungs (an industry “best practice” that is favored by many installers, even when ample cable tray space is available).