All the documentations I could find goes upto only 1000 kcmil. Please direct to a reference for larger cables.

Is there a method to extrapolate from smaller cable sizes?

  • $\begingroup$ You need to provide the stranding. This is because RTS depends on the strand diameter. The core of a strand is softer than the outside. Also, the number of layers causes a derating. $\endgroup$ – John Alexiou Nov 21 '17 at 22:27

Is this the table you're looking for? Burndy, see page O-30 . If I read it correctly, you should be able to plot strength vs cmil for the values in that table and generate a smooth curve which should predict the strength at 2E6 cmil.


I took the Burndy data, ran a lowess smoother followed by a linear regression and got the coefficients tensile = 5.72476410e-02*(cmils) + 4.75077150e+03 , which produces a value for 2E6 cmil of 1.1925e+05 (that's breaking strength in pounds)

Use with caution :-), as that's a serious amount of extrapolation.

I found a value at PriorityWire (PDF) which says 34 200 pounds for Aluminum cable. I suspect that it's rare anyone would go to the incredible expense of using Cu for a strength member, which is why nobody measures the value. Certainly Cu can support its own weight for any run length you can imagine.

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    $\begingroup$ "Certainly Cu can support its own weight for any run length you can imagine." I dunno, I can imagine a pretty long run length. $\endgroup$ – Ethan48 Sep 27 '16 at 16:33
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    $\begingroup$ @Ethan48 yes, well, :-) . Space elevators and all that. $\endgroup$ – Carl Witthoft Sep 27 '16 at 17:44
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    $\begingroup$ indeed if you tried to make a high tension power line of copper the strength/weight would be an issue. Cost drives it out of that job first though. $\endgroup$ – agentp Sep 28 '16 at 1:30

That is a big cable. I am making an estimation here, but let's follow along with my cable analysis:

  1. 1000 Kcmil copper cable has 4 layers over the king strand with 61 individual strands
  2. 2000 Kcmil copper cable with 5 layers of the king strand has $n=$91 individual strands
  3. 2000 Kcmil with 91 strands => each strand $d=$0.148 in^2
    • Use $d =\sqrt{ \frac{{\rm Kcmil}}{1000\,n}}$ where $n$ is the strand count.
  4. Overall size of the cable is $D=$1.927 in
    • Use $D = d (1+2 ( {\rm layers}+1))$
  5. Total strand area is $A=$1.571 in^2
    • Use $A = n \frac{\pi d^2}{4}$
  6. The strand strength factor for aluminum (not pure -O spec) is $\rm sf=$0.965
    • Use ${\rm sf} = 1.1277 - 1.096 \, d$ (taken from a table in the Alcoa conductor manual and curve-fitted with a line.)
  7. I don't have the copper equivalent of the strength factor, but I am assuming it is the same ( approx. similar strength ratio of strand surface to center).
  8. The ultimate strength of copper is $\sigma_U=$62100 psi for fully hard copper.
    • Use solid copper tables and back-calculate from one strand of 0.162 in having rated strength 1280 lbs.
  9. The rated strength of 2000 Kcmil copper cable is 94100 lbs
    • Use $T = ({\rm sf})×A ×\sigma_U$


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