[ProllyInfamous]

>no 240W USB-PD chip has ever gone into production

This is because the cross-sectional-area of the conductor would create an inflexible cable – and even then the connector (even though rated) could never handle a sustained 240W in the real world.

Fires. Fires everywhere... this is why no 240W chip exists.

src: electrician

[nerdsniper]

240W for USB-PD is only 5 Amps (USB spec only calls out for 240W at 48V) which can be safely carried by a standard 16AWG conductor.

USB-IF certifies plenty of USB cables as being tested safe for 240W. The reason 240W chargers don't exist is due to cost and a chicken-and-egg problem. There’s not really any demand for it.

[ProllyInfamous]

My biggest concern is at the actually connector.

Idealized, sure it'll work. But any realworld ports will be arc/fire hazards (e.g. after corrosion, wear, damage).

[Dylan16807]

That's why the 240W design has extra snubbing requirements to minimize arcing.

[ProllyInfamous]

>extra snubbing

Just so I understand: would "extra snubbing" mean the USB-C cable wiggles less when plugged in (i.e. tighter tolerances)?

If so, this would probably mean it'll break/deform easier, too, no?

My above perspective is literally after decades of replacing burned-out devices (both freelance residential and IBEW datacenters), which "technically" are installed correctly — but know their realworld-alities.

[Dylan16807]

There is an electrical circuit that suppresses the voltage spike when you suddenly unplug the cable, to suppress arcing. This improves the immediate physical safety at high power levels, and improves the amount of wear that happens. No physical changes.

[ProllyInfamous]

My lay understanding is that USB-C PowerDelivery isn't even initiated until comms have established the supported wattage? ...or perhaps some very low 5W USB-A-like amount. On sudden disconnect, I presume you're talking about a debouncer (RC) circuit?

----

The concern I have is less about initial arcing (i.e. intentional [dis]connections), and more about long-term sustained powerdraw (I have seen soooooo many melted neutral terminals on 120V receptacles) on a loose connection. Connections become loose for a variety of reasons (including but not limited to bad installation), particularly on thermal throttlers (e.g. small wires, corrosion, cycling).

Does low voltage world have the same 80% derating as insidewireman-land (NEC/AHJ)? i.e. does a 240W PD USB-C allow continues 240W delivery (by protocol/standard/regulator), or is it neutered to 180W for "long-term loads" == 3+hr runtime (e.g. a computer display), with only ≥181W-peaking allowed..?

I just cannot see how such a small connector/cable can deliver sustained 240W, in the realworld that I've lived in.

[Kirby64]

Plenty of USB-C cables are capable of charging at 5 amps continuously and do so today. How is the voltage relevant to how much power is dissipated in the cable? That’s the only difference between a 100W charger and a 240W charger.

[ProllyInfamous]

>How is the voltage relevant

I'm envisioning some future frayedAF school laptop cord, where an increasing voltage correlates to higher likelihood that those amps can more-readily arc/jump (across melt, muck, and matter).

At the end of the day, an increase of either voltage and/or amps calls for a sturdier design (of ports and cables).

[Kirby64]

> At the end of the day, an increase of either voltage and/or amps calls for a sturdier design (of ports and cables).

The cables themselves are already plenty tolerant from an insulation standpoint for 48V. Voltage is low enough to not harm anyone. The ports, as already mentioned elsewhere, are designed to have snubber circuits for rapid reduction in voltage during an unplug. There's a keep-alive to cut voltage as soon as it doesn't detect things plugged in anymore (or, perhaps, the cable gets damaged and can't communicate).

Seems to me like the sturdier design is already accounted for. I don't think "it's small therefore I don't like it" is a valid reason to distrust the standard inherently.

[ProllyInfamous]

>I don't think "it's small therefore I don't like it" is a valid reason to distrust the standard inherently.

Thanks for writing this; it's where I fundamentally disagree, but appreciate your perspective. IMHO that's exactly the problem.