this post was submitted on 18 Aug 2025
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USB-C extensions are not allowed for a reason (www.youtube.com)
submitted 3 weeks ago by Chozo@fedia.io to c/videos@lemmy.world
23 comments fedilink hide all child comments
 

This popped up randomly in my feed today, and I found it to be pretty interesting and informative.

tl;dw: All USB-C cables have a microchip inside them which runs a small bit of software that tells the devices its plugged into exactly what they're capable of, such as their power rating and transfer speeds. When you plug the cable into your device, it reads the data from this chip, which then dictates how much data/power it is allowed to transmit along the cable.

The problem is that when you use a USB-C extension cable, the device you're plugging into can only see the chip data from the first cable; the cables beyond that first one are completely invisible to your device. And if your first cable is rated for 200 watts, and your extension is only rated for 100 watts, your device will still send 200 watts down the line, without ever realizing that it's overloading the extension cable and creating a possible fire hazard.

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[–] ChaoticNeutralCzech@feddit.org 12 points 3 weeks ago (1 children)

They do (if they carry all wires), it's just that they don't add their own current rating into account.

[–] akilou@sh.itjust.works 6 points 3 weeks ago (1 children)

So then do that

[–] ChaoticNeutralCzech@feddit.org 3 points 3 weeks ago (1 children)

I guess there is a way to implement this true to USB-C standard, either with a simple comparison of reported capabilities or a 1-port hub. Somebody would have to make a cost-effective chip that does that though, and manufacturers are happy just printing "max 3 A" on the packaging (if even that).

[–] stoly@lemmy.world 4 points 3 weeks ago (1 children)

The USB consortium has responded to this sort of need over time, but they have to do it in a way that is completely backwards compatible. It might be possible to do this in a new release of the standard, but it may also be that millions of cheap cables would be rendered useless in the process.

[–] ChaoticNeutralCzech@feddit.org 2 points 3 weeks ago

Non-compliant does not mean useless. They will continue to work with devices that use the old standard. PD is already a mess, and especily devices without displays will often fail silently without indication that it's the wrong cable or adapter.