What are cable cleats?
A cable cleat is a device which, when installed along the length of cables, retains and supports them. Cable cleats are typically bolted to a mounting surface (e.g. cable tray rung, metallic strut or weld stud), but do not rely on that surface for the retention of the cables. A properly specified and installed cable cleat is capable of protecting cables by containing the electromechanical forces between the conductors in the event of a short circuit. Cable cleats also protect cables from damage during seismic, vibration and shock conditions, as well as from chafing due to differential movement between cable fixings (a severe problem plaguing marine and offshore installations). Cable cleats provide retention and support to both single conductor and multi-conductor cables.
Why are cable cleats required?
Adequately secured cables can eliminate costly cable repairs, replacements and unplanned downtime. A correctly rated cable cleat, properly specified and installed, will allow you to meet the most stringent cable installation standards. For example, NEC Article 392.8 (D) specifies that parallel connected single-conductor cables are to be “SECURELY BOUND in circuit groups to prevent excessive movement due to fault-current magnetic forces”. If the cable cleat is declared a Category-2 device (per EN 50368:2003), it will be capable of withstanding two successive short circuits, thus allowing the protected cable to remain fully functional after the second short circuit.
Are cable cleats new products?
While relatively new to the US , cable cleats are robust, industrial and mature products that have been effectively used worldwide for over two decades to secure and restrain cables.
What happens to cables during a short circuit?
We are pleased to share two Short Circuit Videos of tests on single conductor 777kcmil, 2kV marine unarmored cables (OD = 1.395”) at 59kA 3Ø RMS-Symmetrical ( 118kA Peak ) short circuit magnitude. During the 0.1 second short circuit duration, the mechanical forces between the cables exceeded 4,500 lbs/ft. These videos graphically demonstrate the necessity for adequate cable restraint and the ability of fault rated cable cleats to prevent excessive movement.
How can I calculate the forces between conductors during short circuit conditions?
The maximum mechanical force between conductors during a short circuit (equation recognized by EN 50368:2003) is:
Ft= [(0.17 x IPEAK2) / S]
Where:
Ft = Maximum Force on Conductor (N/m)
IPEAK = 1st Cycle Peak Asymmetrical Short Circuit Current Magnitude (kA)
S = Spacing between conductor centers (meters)
Example:
A 3Ø short circuit current of 65kA RMS-Symmetrical (143kA 1st cycle peak) flows through three single conductor #4/0 cables (OD=0.8386” nominal +/- 5%) in close trefoil orientation.
Substituting IPEAK = 143kA and S = [(0.95 * 0.8386 * 25.4)/1000] = 0.020235m
►Ft = [(0.17 x 1432) / 0.020235] = 171,798 N/m = 11,544 lbs/ft
Aren't electrical cables fully protected by circuit breakers?
Even for circuit breakers calibrated for instantaneous protection, irreversible cable damage usually occurs in inadequately restrained cables within the first 0.005 seconds (1/4 cycle) of the fault initiation (i.e. before circuit breakers can open). While current limiting fuses may limit the amount of current flowing through the cables, the restraint system must be certified for use at the maximum let-through current for that device.
What are the relevant standards for cable cleats?
The performance standard for cable cleats is European Standard EN 50368:2003, Cable Cleats for Electric Installations. The IEC has formed a project team (SC23A, PT61914) to draft an IEC standard on cable cleats. The principal of kVA Strategies, Charles A Darnell, PE is the US representative on that project team.
What information is required to specify cable cleats?
Our comprehensive Cable Cleat Engineering Specification is free and provides all the information required to specify cable cleats.
How can I learn more about cable cleats?
Contact Us or inquire about our On Site Courses.
With so many available products, which cable cleat do I choose?
You will frequently have multiple options to adequately secure and restrain your cables. Please refer to our Cable Cleat Selection Guide. Alternately, contact us by submitting the Request Information page. Upon receipt, we will promptly contact you to offer recommendations for products meeting your application.
How frequently are cable cleats required?
We have published Emperor Spacing Recommendation general guidelines to accompany the popular Emperor Cable Cleat. For recommended spacing on other products, Contact Us.
