I have never bothered trying to get the earth cable out, takes far too long . just a snip down between the 2 outer core and earth, grabbing the outer core in the same movement and pull the outer core down. Stripped in a couple of seconds. Never had a problem in 30 odd years.



Gary

I rim it at the required length and lightly slice along the cpc route then pull the cpc along the slice line, then pull the sheath away at the rim line.......looks niceand neat in JBs and light fittings.

Legh

Hi Rob. Thanks for the reply, which I now know many will be thinking from their own experience and training, but you expressed it. :-)


I am an old guy who has always sat on his ass and has not exercised for many years. In front of group, someone else, very clever and experienced, no doubt like yourself, told me something similar, but I was suspicious.  So I tried this out in front of the group. I first put ends of copper 1mm then 1.5mm into a vice, a bit less than a yard long. Wrapping the end around a long nose plier and pulling, with no apparent straining by myself or to the observers, I had no difficulty in adding a good 6 inches to the wires. 


Even I was surprised at how easy it was. Now the wire was fresh off the reel so the stretch was nice and uniform, but had there been a kink previously I suspect there might have been significant "necking" in the weakened spot. It is this thought that made me suspect the method and raise the question.

I must say I find 6 inches over a metre quite surprising, although even so  is not a huge reduction in useful cross-section,  but the problem would be damaged or low quality cables.

M.

Total volume is conserved...  I suggest that if any part of the CSA is ever 30% reduced  during pull, you are well on the way to catastrophic failure.

Oddly during this very lunch break I have had a go, only managed between 10 and 15% elongation before failure on a few samples of copper wire now in the bin, much to the amusement of others here. And forces involved were far more than normal wire stripping.

Basically I gently tension the wire and then make marks with a spirit pen on the wire as it passes marks on a reference board. Then I pull to failure, and then measure the spacing of the marks and look at the ratio. Typically marks that were 100mm apart are now 110 to 115mm apart.


Using drawing plates to reduce a wire size or to form a hex or Dflat profile, (Jewellers often do) they try to go down by less that 10% on diameter before re-annealing, as this is the onset of work hardening fractures.

M.

I found that you need to take it steady to get the most elongation. I think that if you go quickly, a smaller segment begins to thin and once that happens, it is the weakest point and fails sooner. It would be interesting to do some properly calibrated experiments.

Of course when using the cpc as a cheese wire it isn't just being stretched, it's being bent under load then pulled straight at each point along its length. What effect that has on work hardening, waisting, nicking etc etc I do not know.

Yes, Copper does work-harden quite easily when bent around to fit a socket. Getting it in the right place the second time is much more difficult because the wire is significantly stiffer. This process does not affect the cross-sectional area, although it moves dislocations and crystal boundaries about. I am surprised that any of you are thinking that the force needed with a PVC cable to extend an already present split (where you got to the CPC in the first place) is sufficient to stretch the wire, it should not be. Metals below the yield point (the force needed to stretch the wire) are elastic and will recover completely when the force is removed, exactly as a spring. If this were not the case bridges would slowly descend in a gentle curve as vehicles passed across! I suggest anyone with a micrometer or vernier caliper (digital) try this test yourself if you don't believe it.2.51.5 will never be a problem, the CPC is much stronger.

I've just pulled some 1.5mm2 to 110% of length before it broke, and yes the force is far more than for cheese wire stripping. I still was surprised how far it went before failure. There is a reason they don't make springs out of copper. and why it is a so-and-so to machine.