Are all (female) USB-C-to-other-port adapters specification-non-compliant, and/or unsafe?
I own a significant amount of male (non-PD) [1] USB-A 2.0, Lightning, and (30-pin) Dock adapters, all of which adapt to female USB-C 2/3[.2]. I never considered these to be non-conformant. However, after purchasing:
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a USB-C female to female “extender” that, in retrospect, was, which killed my Framework 16's motherboard
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a female USB-C to male DC [2] barrel plug adapter that occasionally causes my CREATIVE T60 (speakers) to reboot
…I want to ensure that all of my hubs and adapters (being the implicit extenders that they are) are compliant, and want to know, regardless of whether they are compliant, why they are, or are not safe.
I rid myself of all explicit extenders, so although they're now inapplicable to me, I remain interested nonetheless. However, I retain all of my mere adapters. Some configurations, I am aware are unsafe:
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USB-C to USB-C cables, if merely female at one end or two (which renders the devices extenders, which are impermissible, [3] and with any more ends, they become splitters, which themselves are impermissible) [4] [5] aren't compliant, or safe. [6] [7]
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Passive USB-A (to USB-C) adapters aren't compliant or safe. [8]
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USB-A to USB-A adapters aren't compliant, [9] and male to male adapters aren't safe. [10] Luckily, all of mine are USB-C at one end, but I don't know whether that renders them compliant. I hope so.
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Those inherent splitters and extenders that register themselves as hubs appear to be compliant – they're certainly prevalent – and don't appear to be problematic until daisy-chained. [11] This is more problematic for USB 2.0 than 3.0, [12] although I don't know whether that caveat applies to USB-C, or solely its predecessors.
If any of those are incorrect, please state how. I hope so, but don't expect to be. If anything is absent, please elaborate. That I expect.
From my research, the way to ensure that one remains safe appears to be:
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Don't purchase extenders (especially for USB-C);
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Purchase all adapters with a cable, and ensure that they're male at both ends; and:
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Ensure that all adapters are active
However, I expect that some of those suggestions are predicated on inaccuracies. I certainly hope so, lest I rid myself of all of my uncabled adapters.
Terminology [13]
| Utilised | Alternative | Example [14] |
|---|---|---|
| Female | Receptacle |  |
| Male [15] | Plug |  |
Placement
I posted to electrical. because meta.codidact.com/posts/294825/history#1 accurately advises that this community's participants should know better about this topic than the alternatives offered by Codidact.
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reddit.com/r/AskElectronics/comments/mozxu2/comment/nldxux9↩︎ -
reddit.com/r/UsbCHardware/comments/18rsfdw/comment/kf38ir7↩︎ -
reddit.com/r/UsbCHardware/comments/10xj74r/comment/m8l5tuq↩︎ -
reddit.com/r/UsbCHardware/comments/1i2vgh0/comment/m7hqwei↩︎ -
reddit.com/r/UsbCHardware/comments/1cdbpvi/comment/l1azv9j↩︎ -
szapphone.com/wp-content/uploads/2023/11/usb-c-pinout-diagram.webp[16] ↩︎
1 answer
USB-C to USB-C cables, if merely female at one end or two (which renders the devices extenders, which are impermissible, [3] and with any more ends, they become splitters, which themselves are impermissible) [4] [5] aren't compliant, or safe.
Correct. Cables are only supposed to have male ends. This is true for USB A and B also.
The original reason for this (when there was only A and B) was so that the maximum cable length could not be exceeded. USB was specified from the beginning so that if you can plug it in, you're allowed to and everything will work correctly.
Extension cables obviously violate that because the overall cable can become arbitrarily long. That has implications both for power transfer and signal integrity. The cable is allowed a maximum voltage drop at 500 mA, which can't be guaranteed whith extension cables.
I don't think there is anything unsafe about long cables, at least not with A and B. C can transfer more power, but I'm pretty sure it is required to act like the original USB until some negotiation takes place. Therefore C extension cables are probably not unsafe in that they may break something.
Passive USB-A (to USB-C) adapters aren't compliant or safe.
That doesn't make sense. A common way to connect a USB C device to a desktop computer is with a A-C cable. The device won't be able to draw the high power C allows, and won't be able to reverse roles, but it should otherwise function normally.
USB-A to USB-A adapters aren't compliant, [9] and male to male adapters aren't safe. [10] Luckily, all of mine are USB-C at one end, but I don't know whether that renders them compliant. I hope so.
Again A-C cables are normal and quite common. A-A as just a cable is not allowed, but such a "cable" would be legal if it was actually an unpowered hub.
Those inherent splitters and extenders that register themselves as hubs appear to be compliant – they're certainly prevalent – and don't appear to be problematic until daisy-chained. [11] This is more problematic for USB 2.0 than 3.0, [12] although I don't know whether that caveat applies to USB-C, or solely its predecessors.
Yes, the correct way to physically extend USB is with a hub. That only "extends" the USB in appearance. Each side of the hub is actually an electrically separate USB. The hub does the necessary packet transfers and translations in between.
Such hubs usually have their own power supply, so can fully power multiple downstream ports simultaneously.
There are such things as unpowered hubs. Those use the limited power from the upstream host to power themselves and the downstream devices. They will be forced to disallow devices that take too much power. Now that power supplies are small and cheap, such hubs are not very common. In practice they are useful only for small devices like a keyboards and mice.
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