Wire size is calculated off the 75C column of the ampacity table (NEC 310.16) so #12 wire is only good for 25A.
The reason being, there are almost no circuit breakers rated for 90C, the terminals/lugs are only rated for 75C in nearly all cases.
Forum thread w discussion: https://forums.mikeholt.com/threads/90-degree-or-75-degree.2...
I don’t think anyone needs shared fiber and 12ga cable in a home setting anyway.
The NEC also defers to UL and similar bodies for installations being cleared so the complexities go beyond the basic NEC guidance, especially for the exotic stuff out there.
You also need equipment lugs/terminal blocks/wire nuts rated for 90C.
I’m not saying 90C rated parts don’t exist, it’s just uncommon enough that you select wire based on the 75C column by default, even in a commercial setting.
Right now you can buy 50m USB3 cables made of 'Active Optical Cable' which is a fiber data link with two copper wires for power.
Options start at ~$100 for 50m https://www.aliexpress.com/item/1005004105594973.html and prices go up to https://www.lindy.co.uk/cables-adapters-c1/usb-c449/50m-hybr... - not cheap, but considering how few they probably sell and that you're getting a special custom type of cable, kinda affordable.
I can't quite explain it, but... having not known of the existence of such cables, and despite the fact that it's good I don't have a use for one since they're not exactly cheap, there's something about them that makes me want to buy one.
I've really no idea why, but I even spent a few minutes wondering if there's anything I've never done due to not having a cable like that, but didn't think of anything.
(And it's not like I'm a cable collector or enthusiast or anything like that, generally!)
Any ideas of reputable brands for optical display port (and miniDP) cables?
Did a quick search and the first version was £80 for 10m / £100 for 20m on Amazon from one of those shitty, random name Chinese "companies" (in this case called "ATZEBE), which wouldn't surprise me if it was actually just the cheapest DP cable of the right length they could find rather than the real deal. (Not that I'd trust buying any cable on Amazon, even one they claim is sold directly by a company like Apple, considering Amazon's co-mingling system leads to any time they claim "sold by x company" has for years actually meant "one or more of the stock we have for this item is sold by the company that its claiming to be made by, good luck hoping you get one of the legit ones".)
And thinking about the two options that user michaelt linked in the comment I replied to just above you:
> "Options start at ~$100 for 50m https://www.aliexpress.com/item/1005004105594973.html and prices go up to [£450 / $570 USD for 50m at:] https://www.lindy.co.uk/cables-adapters-c1/usb-c449/50m-hybr...
To what extent is the expensive one the equivalent of an audiophile getting a placebo effect from using overpriced audio cables that make no difference in a blind test, vs. it being the price needed for a good quality 50m optical/hybrid USB cable while the cheap one linked on AliExpress might either perform worse, last less long, or be an outright scam like those fake USB storage sticks that are hacked to tell the OS that they have more capacity than they actually do?
Also compare to data center hardware. A 10m 10gbps active optical cable is only $31 retail: https://www.fs.com/products/30895.html
Normally you'd buy optics and fiber (which is cheaper than copper ethernet cables of the same length) separately for data center use and in larger volume, but my point is that there's no expensive tech involved in these cables.
Having now done retrofit Ethernet install in a 75 year old house, if I ever build a new house it's going to have low voltage conduit from attic or basement to every interior wall and one or more big conduits from attic to a single home run location, itself with a dedicated 20A circuit.
Though I do know there's a company out there that makes manufactured 2x6 stud (tstuds is one name) that's basically 2 3x2's with diagonal pins between them. Quieter, less thermal transfer, and cheaper to make high R outside walls since the cost scales faster with length than width. Snaking a new cable through an interior walls made of that stuff would just require your typical fiberglass pole, with little to no drilling.
I learned the other day that this is actually a thing one can buy. Direct bury hybrid fiber copper, up to looked like 2 OS2 strands and 2 12awg copper conductors. It's fantastically expensive but might be worth it for certain applications, like cameras that are beyond PoE distance limits and also don't have power available.