How are USB-C cables so thin?

Question

Looking at the plug of a USB-C cable, there are 24 different pins. With a Micro USB cable, each pin corresponds to one wire inside the cable. In my understanding, this means that a USB-C to USB-C cable should have 24 individual wires inside.
How is a USB-C cable able to be so thin, or does the cable have less wires somehow?

Answer 1

Well, by using thin wires of course.

That they're rated to handle the current they are (~2A), is... kind of ludicrous, but how the copper is allocated, matters. And, they might not be rated for full current.

The one saving grace is, they're short so resistance isn't as big of an issue, and as long as the internal temperature seems to be okay, there you have it. Until you don't, and, failing connectors are a notable problem (the equally tiny contacts heat up more, they wear quickly, etc.), as well as fraying cables themselves (foil in particular doesn't flex well, and then the rough broken edge can dig into the insulation, fatigue the braid, and further breakdown ensues).

Food for thought, consider this picture by TubeTime:

Seems to be a special one, using micro-coax instead of twisted pairs; if all the center conductors are VBUS as labeled, the shields must be serving as GND. Only the USB 2.0 pair uses foil.

Another one shows a more typical foil-wrapped pairs construction:

Source: https://commons.wikimedia.org/wiki/File:Cross_section_of_a_10Gbps_USB_cable.jpg

In both of these examples, the smaller conductors around the side are probably CC/SBU 1/2. On this one, they appear to be individually foil wrapped, except for the yellow wire strangely. Rule is mm, so this cable is ~5mm across, not terribly thin, but they can make them thinner by basically shrinking all dimensions proportionally, give or take what they can get away with for the power wires (e.g., shrinking the data pairs more to keep the power wires large). Also, the CC pins might be wired to a circuit that enumerates the cable's current rating, permitting thinner construction.

Smaller transmission lines have increased losses, restricting the maximum length in a given SuperSpeed mode; it's no accident that most USB3 cables are on the short side. I haven't looked up the typical specs across the range of available cable sizes and lengths, but I expect the thinner ones aren't available as long due to signal loss.

You can find more cross-sections and close-ups of common and vintage electronics in: Oskay and Schlaepfer, Open Circuits, 2022, No Starch Press, ISBN 9781718502345, https://nostarch.com/open-circuits

Answer 2

There are different types of cables. Some can be thin, some cannot be. None of them will have 24 individual wires though.

Simplest ones don't have all the wires, as they are just for USB 2.0 and are rated for 3A current. They can be very thin and very flexible. 5 wires is enough.

The most complex cables support video transfer in DP Alt Mode and are rated for 5A current and may contain active signal buffers or converters at one or both ends. They can be quite thick and stiff to bend to protect the delicate high speed cabling from damage, as too tight bends ruin the high speed properties.

It still does not require 24 wires, as typically the four VBUS and four GND pins do not have individual wires and due to connector being flippable you only need one USB 2 wire pair. So 4 HS data pairs, 1 SBU/AUX pair, 1 USB2 pair, VBUS, GND, CC and VCONN is only 16 wires.

The supply wires that carry high current are typically much thicker than the high speed data wires that can be very thin.

Also in general you need thicker wires if you intend to make a longer cable and thinner wires if you make a shorter cable.