An electrical experiment for Easter

Chris Pearson said:

A USB charger (Apple Model A1696) was plugged into the adjacent socket-outlet. A USB-C to USB-C cable was plugged into the charger and the other end was immersed in the sodium chloride solution. The charger was energized.

Correct function of the charger was confirmed after the experiment. Confirmation that the earth was effective was obtained by measuring the earth fault loop impedance at the socket outlet.

Results

No current flow was detected. The EFLI was 0.80 ohms.

I would question whether your experimental technique is a valid representation of the real-world risk of a USB device in water, because the more recent versions of the USB standards, including USB-C are not a simple, always-on, DC power supply but rather they have a set of communications protocols and hand-shaking between the host and the connected device, whereby they communicate details of the respective devices, power capacity (volts/amps) and (from a quick skim read of Wiki) it looks like the host (i.e power supply) might be checking for certain conditions at the device end of the cable before powering up the supply. 

So it's possible that with a compliant USB-C power supply and USB-C cable, the plug you immersed into the solution may not have been powered up at 5V at all.

There's also the question of 'Power Delivery' functions which allow the USB power supply to raise the supply voltage above 5V depending on the connected device, in a real-world situation a lot of newer USB-C power supplies have PD functionality, so connected to a phone could be providing upto 20V if turbo-charging the phone, but to test that would require a suitable power supply and device on the end of the cable, or some other way of ensuring the power supply was outputting the higher voltage onto the USB-C plug when immersing it into water.

Chris Pearson said:

A USB charger (Apple Model A1696) was plugged into the adjacent socket-outlet. A USB-C to USB-C cable was plugged into the charger and the other end was immersed in the sodium chloride solution. The charger was energized.

Correct function of the charger was confirmed after the experiment. Confirmation that the earth was effective was obtained by measuring the earth fault loop impedance at the socket outlet.

Results

No current flow was detected. The EFLI was 0.80 ohms.

I would question whether your experimental technique is a valid representation of the real-world risk of a USB device in water, because the more recent versions of the USB standards, including USB-C are not a simple, always-on, DC power supply but rather they have a set of communications protocols and hand-shaking between the host and the connected device, whereby they communicate details of the respective devices, power capacity (volts/amps) and (from a quick skim read of Wiki) it looks like the host (i.e power supply) might be checking for certain conditions at the device end of the cable before powering up the supply. 

So it's possible that with a compliant USB-C power supply and USB-C cable, the plug you immersed into the solution may not have been powered up at 5V at all.

There's also the question of 'Power Delivery' functions which allow the USB power supply to raise the supply voltage above 5V depending on the connected device, in a real-world situation a lot of newer USB-C power supplies have PD functionality, so connected to a phone could be providing upto 20V if turbo-charging the phone, but to test that would require a suitable power supply and device on the end of the cable, or some other way of ensuring the power supply was outputting the higher voltage onto the USB-C plug when immersing it into water.