I recently bought a 250-foot bulk box of Cat6 to do some custom-length Ethernet runs through my house, and I did what a lot of people do: go to Amazon, search for the product, buy the one at a decent price and a plethora of reviews. When I stripped a conductor and dragged a knife blade across it, the copper peeled away to reveal that the cable was actually copper-clad aluminum instead of solid copper, which wasn't immediately alarming, because the cable and listing were marked as such with "CCA."

After looking through the Cat6 specification myself, though, I came to find that any cable using aluminum for conductors doesn't actually qualify as Cat6. Some of the best-selling cables and cable rolls on Amazon are CCA "Cat6", and while they're fine for the odd patch cable, trusting these cables to carry a 5+ GbE connection or PoE can carry not just performance consequences, but potential safety ones as well.

It's a real Ethernet cable that can carry Cat6 speeds in theory

But it's not real Cat6

Copper-clad aluminum cables are exactly what they sound like: an aluminum conductor with a thin skin of copper that's been deposited around the outside. The obvious reason for doing so is cost-cutting, because aluminum is much cheaper than copper, but the physics argument also makes sense. High-frequency signals tend to travel along the outer surface of a conductor thanks to the skin effect, so the theory goes that the data riding the copper skin doesn't much care what's underneath. For the signal, it holds somewhat true for shorter runs, but the problem comes with everything else.

I won't bore you with the electrical nitty-gritty, but Aluminum has roughly 61% the conductivity of copper, which translates to about 55% higher DC resistance for the same gauge of wire. In layman's terms, that higher resistance means more attenuation, and attenuation is exactly what eats into your margins on longer runs and at the higher frequencies Cat6 is supposed to handle. Aluminum is also more brittle, so it's likelier to crack at a termination point, and the aluminum oxide that forms when it's exposed to air doesn't conduct. That can easily result in a connection that feels fine one day, but degrades over a period of weeks.

This is exactly why the standards bodies don't leave it open to interpretation. ANSI/TIA-568.2-D requires the conductors in Category-rated cable to be solid or stranded copper, full stop. ISO/IEC 11801 says the same. A cable built with CCA conductors isn't a Cat6 cable at all, despite the label being printed on the jacket and on the storefront listing. To be fair to this company, though, it is marked as CCA, so partial credit is due.

PoE should stay far away from aluminum

You need full copper

The skin effect that helps keep a CCA cable viable for carrying a Cat6 data signal does nothing for Power over Ethernet. PoE is DC, and DC doesn't ride the surface in the same way. It sees the entire cross-section of the conductor, which is mostly aluminum, and all of that extra resistance shows up as two things: heat in the cable, and voltage drop by the time the power reaches your camera, access point, or doorbell. The practical result is usually a device that browns out or refuses to power up, especially on longer runs, and it gets worse as the power budgets climb.

It gets worse: CCA can't carry a valid UL fire rating, which means running it inside a wall, between floors, or through a plenum isn't just inadvisable, it's outside code in most jurisdictions that have adopted the National Electrical Code. That can void the listing your insurer assumes you have, and it can put liability on whoever installed it. Patch cables that sit outside of your walls could also fall outside of code, and in the event of an unrelated fire, a CCA cable being found could raise serious compliance questions, though that's a bit of a gray area.

Some go as far as to say CCA cabling is a serious fire hazard that can burn your house down, but the picture is a little more nuanced than that. There's no wave of homes catching fire because someone ran cheap Ethernet, and the much more realistic failure you'll see is an underpowered device or a connection that degrades over time in addition to the fire rating you no longer legally have. In my brief research I couldn't find any evidence of a fire being caused by CCA Ethernet cable, and just using it for data alone almost certainly could not cause a fire. If you're running sustained 48V PoE where corrosion is involved in a worst-case scenario, I could see that being a serious fire risk, but they're certainly still a far-cry from the aluminum-branch-wiring house fires of the 1970s.

How to tell if your Ethernet cable is CCA

It'll probably be printed somewhere

Start with price: pure copper has a hard cost floor, so if a roll is dramatically cheaper per foot than everything around it, that's your first flag. Pick it up, too. Aluminum is lighter, and a box of CCA feels noticeably less hefty than the same length of copper.

The jacket is the other dead giveaway. Honest sellers sometimes print "CCA" right on the cable; many print nothing at all, or bury it off the Amazon listing and only admit it on the packaging. Real copper cable tends to advertise the opposite loudly: "bare copper" or "solid copper," a UL listing, and length markings.

If it's a bulk roll, the simplest way to tell is by doing what I did: strip back a conductor and scrape the surface of it with a knife. If you scrape and see anything silver, your cable is CCA. If it's a pure copper cable, it'll be copper all the way through.

CCA isn't a grand conspiracy, but it is worth looking out for

For strict data use-cases where you're not planning on pushing the limits of what the Cat6 specification is capable of, CCA cable is absolutely fine. But "Cat6" printed on a copper-clad aluminum roll is a claim the cable simply can't honor, and it does leave a legitimate gap at the high end. Any type of long run, PoE usage, or anything permanently closed up in your walls should be full copper cabling, and nothing less.