[bitcraft]

240W with USB-C operates at 48 volts.

[yummybear]

Is this safe for humans? Like if my daughter were to suck on the cable.

[SV_BubbleTime]

Your daughter would first have to enumerate and negotiate to switch from 5VDC to 20-48V of USB-PD.

So if she can do that with her mouth, you have other things to worry about. (She’s an android, not some colorful euphemism).

[onetwentythree]

Yes. Power supplies up to 60VDC are typically designed to fall under SELV and are considered intrinsically safe. SELV requires isolation and a single fault tolerant design. Here is some additional info:

https://www.edn.com/what-does-selv-mean-for-power-supplies/

I doubt the USB-C power negotiation feature is specifically a safety function, but as other comments have pointed out it makes the system even safer.

I haven’t looked at the spec, but I wonder if there is any functionality that prevents a power supply from applying 48V all the time. i.e. is it possible to deliver a functional charger that is not SELV and has no power negotiation?

[detaro]

it's not, since a device has no obligation to be able to handle 48V input.

[atonse]

Usually it negotiates up (thats what USB PD is)

Like the device it’s plugged into actually has to communicate and negotiate that it wants something higher.

Until then it’ll just be I think 5V and up to maybe 1amp? (5W)

[zw123456]

Also, old timey phone lines, like back in the day when you plugged a phone into the wall, that had 48V DC on it. But not 5A, mor3 like 600ma. But in theory, not enough to kill.

[SV_BubbleTime]

48 approaches but usually doesn’t exceed what it takes to enter dry skin.

But also USB-PD doesn’t start at 48VDC.

And it is constantly monitoring for shorts. So if you did manage to get shocked it would only be for milliseconds.

[rasz]

You did have a phone landline at one point in your life, right?

[zw123456]

oh snap, I should have read up on that. That's interesting though, same as telco.

[SV_BubbleTime]

It’s not really the same. The 48VDC of USBC is switched and will be constantly monitored for over or unusual current. A telco doesn’t care and will allow draw to its full potential all the time.