3 Conductor cable whip 1

[bobo480]

thread238-191953

I'm trying to find some information about Cable Deflection during short circuit conditions on a 3 phase four conductor "drop" cables. I remember seeing a video about cable deflection during a short circuit and seem to remember the unsecured cables move about violently. Is cable deflection to be expected when dealing with 3 conductors in a bundle (#2-4 cond SOW)

The temporary cable which is protected by a GE THED 100 amp breaker is 100 ft. in length. The current method of securing using plastic zip-ties is being questioned.


Thanks,

 

[7anoter4]

From the thread238-191953 as Marmite wrote:
"For single core cables you do get substantial magnetic forces between the cables under fault conditions".
It was about single core cables.
Your 4*2 awg SOW cable it is a multi- core cable where all 4 cores are surrounded by a strong jacket with a good mechanical stability under short-circuit case. See for instance:

http://www.wesbellwireandcable.com/PortableCord.html

The cleats or clamps you need only in order to maintain a distance between cables as required by code- only for cooling purpose in steady state load.
For single core cables in order to calculate the maximum force ,you have to now the steady state short-circuit current ,multiply this by 1.8-2 factor for peak short-circuit current and calculate the maximum force F=0.2*Ipeak^2*length/distance F[N-newtons];Ipeak[kA];length and distance [m]. See:

http://dept.physics.upenn.edu/~uglabs/lab_manual/force_between_conductors.pdf

 

[bobo480]

Thank you for your helpful reply.

I discussed this with a cable "cleat" manufacturer and they claim that the SOOJ jacket is not rated to withstand the repulsive forces generated as a result of short circuit currents. They claim the jacket will most likely fail violently above 18 kA. In this particular case the available current is 20 kA.

Below is their justification.

"The IEC calculation based on a center-to-center conductor spacing of 10.46mm (7.42mm conductor + 3.04mm insulation thickness) and a peak current of 15kARMS * 1.6 * Sqrt(2) = 33.9kAPEAK, the result was 18.7 kN/ meter (1,258 lbs-force/ foot). The result seems excessive for cable ties. Suggest that cable cleats be applied at 10’0” lineal centers and at the beginning and end of each 90° cable bend to contain the conductors in the case of a 3-phase short circuit.

The calculation results are repeated below:

Electro-Mechanical Force Between Cables (Maximum): FT = (0.17 x IP2) / S (formula from IEC 61914:2009, Appendix B)

S (Center-to-Center Conductor Spacing): 10.46 mm

3Ø RMS Symmetrical Short-Circuit Current: 15.0 kA

IP (1st Cycle 3Ø Asymmetrical Peak Short-Circuit Current): 33.9 kA

Recommended Ellis Patents Cable Cleat/ Strap: Emperor Single, Vulcan or ProTect Strap (model numbers TBD based on overall cable diameter)

Maximum Horizontal Lineal Cable Cleat/ Strap Installation Centers: 120.0 inches

FT (Resultant Force between Cables): 18.72 kN/ meter = 1,258.1 lbs-force/ foot