Confusion Still Reigns Over USB-C/Thunderbolt Cables

It is hard to believe the vast amount of confusion that continues over cables with USB-C/Thunderbolt connectors. These cables may be the future of computing, but right now they are a big, sloppy confusing mess. The problem is cables that handle USB-C, Thunderbolt 3 and USB 3.1 all have the same connector and look alike but do different things.

Apple introduced USB-C to its customers with the 12-inch MacBook in 2015. At the time, it was a basic USB port that could power the Mac from an external source and officially called USB 3.1 type C Generation 1.

Appleinsider, a publication for all things Apple, tried to explain the confusion in a recent article. It notes the same physical port was used in the 2016 MacBook Pro refresh, offering a faster, more capable Thunderbolt 3 connection with the same USB-C physical connector. And now, the MacBook Air and Mac mini has Thunderbolt 3, and the iPad Pro is a USB 3.1 type C device, instead of Lightning.

Put simply, Appleinsider said, USB-C as a term by itself means nothing about data speed or charging ability. It is literally, and only, a description of the physical connector. Thunderbolt 3 at 40Gbit per second has to have USB-C at both ends. USB 3.1 at 5Gbit per second or 10Gbit per second does not. Both share the same physical USB-C connector for the host device, though.

To make it worse, there are seven USB-C cables and seven different specs. Complicating matters even more, some Thunderbolt 3 cables can function as a USB 3.1 type C cable — but not all can. A USB 3.1 type C cable is never a Thunderbolt 3 cable, despite having the same connectors.

Various types of cables

Various types of cables

Also, not every USB-C cable — be it Thunderbolt 3 or USB 3.1 Type-C — is capable of providing 100 watts that is allowed in the specification. In fact, between poor quality cabling available at multiple venues, nonexistent cable markings and Apple's obsession for plain white cabling, this is more confusing now than ever. There has been no improvement in the last two years.

With the MacBook, the MacBook Pro since 2016 and now the MacBook Air and iPad Pro, Apple includes a USB-C charging cable. A 15-inch MacBook Pro cable is rated for 87 watts when plugged into the appropriate MacBook Pro adapter. It can be used on the MacBook and 13-inch MacBook Pro at appropriate wattage.

The converse is true, but the combination will only supply charging power of the lowest rated component, be it cable or AC adapter. For example, an 87 watt power adapter with a 60 watt-rated cable will only provide 60 watts to the host computer.

The Apple-supplied cable is only capable of USB 2.0 speeds, and is in no way a Thunderbolt 3 cable. This isn't unique to Apple, though — most high-power USB-C cables found on Amazon are only capable of USB 2.0 speeds.

The website said it had a selection of very short Thunderbolt 3 cables pass through the testing lab while they’ve gone through the docks, eGPUs and other Thunderbolt 3 peripherals. None of them arrived clearly labeled on the cable itself. Some are capable of 100 watts. Some aren't. So, that itself becomes a major problem.

At present, there is no chance a Thunderbolt 3 device will connect at all with a USB 3.1 type C cable, despite the cable fitting and even possibly providing power to the peripheral device. This may change for newer peripherals, as a change in the spec and a modernization of controllers will allow for failback. This means a Thunderbolt 3 peripheral will ultimately be able to use a USB 3.2 Type C cable for connectivity, but at the slower speed that the protocol allows.

Most Thunderbolt 3 accessories come with 18-inch compatible cables, but they are mostly useless because the cables are cripplingly short. Users shopping for longer cables aren't being greeted with universal language, or with complete specifications in every case.

The short Thunderbolt 3 cables that come with docks and other peripherals are generally passive cables. To keep costs down, passive cables are no-frills cables, and because of it, runs longer than 18 inches have slow transfer speeds for connected devices. This can cause problems in high-bandwidth situations like docks or high resolution displays.

Short, passive Thunderbolt 3 cables, such as those packed-in with docks, are very nearly always fully compatible with USB 3.1 type-C peripherals. But, the length is the problem.

Thunderbolt 3 runs longer than 18-inches can be passive or active. The passive ones have lower speed, with the max data rate hitting about 20Gbit/second at two meters of cable length. However, at present, active cables contain transceivers to regulate the data transfer through the cable. At the same two meters, speed is still at the maximum of 40Gbit/second.

Passive cables maintain USB 3.1 type-C compatibility. Active ones generally do not. There is no correlation between passive or active, and maximum wattage. And, that USB 3.2 speed failback? It likely won't be backwards compatible to older cables or peripherals.

Looking for the data rate isn't enough when shopping for Thunderbolt 3. Searching on 40Gbps doesn't tell you if the Thunderbolt 3 cable in question is passive or active.

The industry has spoken out about the issue, but hasn't mandated the use of the iconography leaving it up to the user to be clear on what's what. This needs to be mandatory, and permanently affixed to the cable somehow, with common labels that at the very least can be looked up.

About a year ago, Intel started shipping the Titan Ridge chipset for Thunderbolt 3. There is no certainty if it made the situation better or worse overall, but for the first time, a universal USB-C cable, capable of USB 3.1 type C or Thunderbolt 3 supplying up to 100W on a two-meter cable run is possible at a cost. This universal cable isn't on the market yet.

For the time being, Appleinsider makes these recommends. Hard drives, even most small-scale RAID arrays, aren't that demanding. Passive, long Thunderbolt 3 cables, such as that from Plugable at 20Gbps, work fine and won't take a speed hit. They also work with USB 3.1 Type-C printers and other accessories. Obviously, if you have a RAID, SSDs or an external NVMe drive use 40Gbps.

Recommended is the Cable Matters 40Gbps 6.6 foot cable. It has reliable connections and can provide 100 watts of power. But it is not cheap at $57.99. While currently recommended for the most demanding applications, the cable is not compatible with USB 3.1 type C applications.

For users needing a USB 3.1 Type C, buy that. Don't pay the premium for Thunderbolt 3. Be mindful of reviews in addition to maximum power limitations if a 15-inch MacBook Pro is going to be charged. Appleinsider likes the Anker Powerline II USB-C to USB-C 3.1 gen 2 cable for most connectivity and power needs given that it is rated for 100 watts and full 10Gbit/sec speed. However, it is only three feet long.

As a quick cheat-sheet: Active Thunderbolt 3 cables are high-speed but expensive, and mostly lack USB 3.1 Type-C compatibility — but very new ones might retain it. Passive Thunderbolt 3 cables are generally short for best performance, and nearly always maintain USB 3.1 Type-C compatibility. Neither passive nor active imply anything about maximum charging power, nor are they necessarily labeled on the cable indicating what they are capable of delivering.

And finally, two years after the introduction of these cables, it is up to the end user to label them. It'll save time and confusion in the long run.

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