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I got an Ethernet cable on Amazon for what was, in hindsight, a suspiciously good price. The description says it's copper but one of the one-star reviews claims it's actually copper-clad aluminum (CCA). It would be easy to verify the cable's composition by cutting, stripping, and scratching or burning one of the wires, but is there a non-destructive way to determine whether it's copper or CCA?

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    \$\begingroup\$ If you’re lucky and have a friend with a portable handheld XRF spectrometer, then you can just ask them to zap it for you. Post a link to the cable in question. \$\endgroup\$
    – Ste Kulov
    Commented Jun 28 at 16:52
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    \$\begingroup\$ you can usually see the end of the wire through the connector plastic ... examine the cut end with a microscope \$\endgroup\$
    – jsotola
    Commented Jun 28 at 18:57
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    \$\begingroup\$ @MOSFET This is dodgy tat from Amazon we're talking about here. The brand name is probably a random string of letters that was registered as a trademark to meet Amazon rules. The manufacturer is most likely a company in China. The odds of getting a correct answer from them are pretty slim. \$\endgroup\$
    – Simon B
    Commented Jun 29 at 11:33
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    \$\begingroup\$ For communications purposes, pure copper and CCA would have pretty similar performance. Due to what's called skin effect, at high frequencies only the outermost few microns of a conductor actually carry any current. So unless you're using POE (which involves DC superimposed on the cable), both should have pretty similar performance. (some low-loss coaxial cables even use copper-clad steel, because steel is cheap and good low-frequency performance isn't a design goal.) \$\endgroup\$
    – Hearth
    Commented Jun 29 at 15:35
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    \$\begingroup\$ @Hearth correct - CCA performs within-specification for Ethernet, and its cheaper. Digital data doesn't degrade like analogue, you do not need fancy patch cables unless you're pushing the distance limits or dealing with interference. And as OP notes its CHEAPER for the end user. CCA vs Copper won't make one's internet faster. \$\endgroup\$
    – Criggie
    Commented Jun 29 at 22:52

2 Answers 2

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Since the resistance of copper is different than the resistance of aluminium, you can measure the electrical resistance of the line and see if it matches the expected value for the gauge the vendor is claiming.

Typically this matters in the context of POE, so you could also simply use it with a POE device and see if the voltage drop is what you expect for a known good cable.

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  • \$\begingroup\$ Comparing with a known good cable is the safest, I think. Unless the spec for twist rate is given (there is no standard, just a range) it could be rather hard to estimate the correct conductor length from the cable length. \$\endgroup\$
    – MrGerber
    Commented Jun 28 at 17:15
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    \$\begingroup\$ Twisting adds very little length, e.g 2%, on the other hand the resistance difference between Cu and Al is ~60% \$\endgroup\$
    – fraxinus
    Commented Jun 29 at 7:38
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  1. Measure the resistance as suggested by @user180479. Aluminum has a resistivity about 1.6 times higher than copper.

  2. Weigh the cable an see how it compares to solid copper cable. You should get a good idea just by hefting the cable in your hand. Copper density is about 3.4 times higher than aluminum.

  3. If it's copper-clad aluminum, you can scrape away the cladding with a modeling knife and see if the core is silver-colored. You can also try soldering to the exposed core. If it repels solder, it's aluminum.

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    \$\begingroup\$ The method 3 is destructive, method 2 suffers from the small and not exactly known proportion of metal vs plastic in an Ethernet cable. \$\endgroup\$
    – fraxinus
    Commented Jun 29 at 7:42
  • \$\begingroup\$ Method 1 suffers from errors in contact resistance that gets worse as the cable gets shorter. \$\endgroup\$
    – MOSFET
    Commented Jun 29 at 23:12
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    \$\begingroup\$ @MOSFET True, which is why a 4-wire ohmmeter and something over 10 metres cable length is helpful. \$\endgroup\$
    – qrk
    Commented Jun 30 at 15:56
  • \$\begingroup\$ That’s exactly why I asked the questioner for the length of the cable or to just post the Amazon link for it. But there was no response… \$\endgroup\$
    – Ste Kulov
    Commented Jul 3 at 0:08

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