An electrical experiment for Easter

Morning Chris

I am aware of 3 such type fatal accidents. One in the UK and one in Germany involving IPads being used in the bath.

I have also read the coroners report from the Anne Marie OGorman fatal accident which in volved an IPhone supplied whilst the victim was using an IPhone supplied from a long USB lead pluged in to a charger inserted in to a hall socket outside the bathroom.

There is no doubt that the poor woman died from ventricular fibrillation with additional evidence of burns to her body. I understand the plug in charger was not an OEM device. 

Your experiment was interesting and as a collector of AVO 8s I am aware of the value of the instrument still for some forms of testing. However the input impedance I think is 2000 ohms/volt. If you had used an electronic muti-meter rated for the the voltage, rather than one used for electronics, it will have produced as different reading due to the higher input impedance. 

Following the German accident I did some experiments on my own Ipad connecting a high input impedance voltmeter on the back I was detecting I remember correctly something in the order of 120V. I then used an oscilloscope to see the peak voltage and it was in the order of 180V with a distorted waveform.

Being immersed in water substantially increases the risk  of fatal shock hence all of the provisions of BS 7671 701. 

I believe investigations on the Irish fatal accident are still being worked on. 

JP

A (standards conforming) USB port will always (assuming it hasn't been turned off in some way) have 5V on it and be capable of delivering 100mA, before anything is plugged in.  There are various ways in which the port and the connected device can then negotiate different voltages and currents, up to 5A at 48V (notably the USB Battery Charging and Power Delivery Specifications), assuming that those voltages and currents are supported at both ends (and in the higher power cases (more than 20V or more than 3A), by the cable itself which also has to contain an electronic ID which is validated before allowing the higher powers).

High end phones now charge at 45W or more with a USB charger capable of delivering at least 15V, after negotiation.  I suspect that in many cases those phones are only charged at ~2A @ 5V most of the time as that is what most non-OEM chargers will deliver.

TurboGen said:

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.

Thank you. Yes, I had considered that possibility.

I have no idea whether my chargers are that clever.

John Peckham said:

I understand the plug in charger was not an OEM device. 

John, thank you. It was a toss-up between the AVO and a Fluke digital meter.

I bought a new iPhone about 13 months ago. Because of the EU's Common Charger Directive, it uses a USB-C port rather than a proprietary one, and it came without a charger.

That makes very good sense from the point of view of avoiding waste, but it also opens the market to chargers which may be of a lower quality than OEM.

I wonder what sort of warnings come with a generic charger?

Are you sure that is correct for USB 2.0 on USB Type C ? I wouldn't disagree for the earlier USB versions, but have 2.0 / Type C changed this?

I don't work on USB standards, but I've seen some sources stating that USB-C requires a specific pull-down resistance be applied to one of the pins, CC, to trigger the host device to power up the V-Bus. Suggests that without the required pull down resistor, V-Bus is switched off.

DShutt said:

A (standards conforming) USB port

It's not the USB end that is the [source of] danger, but the power plug, it's adapter, and the wider EMC and product design standards (real or imagined).

Bad component select, lack of galvanic isolation, addition of EMC filters, assumptions about 2 vs 3 pin power all play a part in the safety (or lack of) for the usage of the charger in scenarios like these. 

It (understanding) is made worse by the rareness of the events and consequent 'poor' failure analysis after the event.

I greatly doubt that the charger was operating 'normally' and yet creating a fatality. 

We may be doing that 'searching for the car keys where the light is better' rather than the darker truths...

Sadly John, as you look abroad, there have been quite a few more in the last few years. 

As I can read German, there is a bit of a bias here to Austria, Germany and Switzerland; but I think we should assume that other places are probably similar at the one or two in hundred million years sort of level.

https://www.derstandard.at/story/2000146130189/handy-rutschte-in-die-badewanne-junge-italienerin-starb-weil

https://www.blick.ch/ausland/weil-ihr-ladendes-iphone-ins-wasser-fiel-24-jaehrige-stirbt-in-der-badewanne-durch-stromschlag-id16237529.html

https://www.sueddeutsche.de/muenchen/handynutzung-stromschlag-in-der-badewanne-16-jaehrige-stirbt-beim-musikhoeren-1.4375817

https://www.20min.ch/story/handy-faellt-in-die-badewanne-dann-ist-mariantonietta-16-tot-890987304474 

Interestingly, for females it is now approaching  the no of fatalities from twisted hairdryer flexes failing, the traditional continental mains in the bathroom Bete Noir.

Due to our regs, in the UK, hairdryers explode mostly in the bedroom but still in similar numbers.  (while the hairdryer in Spain fails mostly over the basin.. ) 

Given the no of tangled mess leads I have repaired over the years, it is clear that most such failures are non-fatal, and just result in unlady-like language.

There is no doubt in my mind, that this new trend shows that mobile phones are indeed bad for you.

Careful with that Ipad.

Mike.

The Electrical  Equipment (Safety) Regulations  requires manufacturers, importers and distributors to supply a Declaration of Conformity (DoC) for products they intend to place on the UK market. On of the provisions of this Statutory Instrument is to supply instructions in English with their products. 

JP

At the cheap end, none, and there are more than a few designs where the insulation creepage and clearance distances are far less that the proper standards require and a spot or two of condensation could bridge things out to the tune of a lethal no of mA 

This danish chap reviewed a load

https://lygte-info.dk/info/ChargerIndex%20UK.html lists some - any with a skull and crossbones review are non compliant.

Hs looks at many Europlug  models and a UK Example here 
https://lygte-info.dk/review/USBpower%20UK%20Plug%20style%20USB%20charger%201A%20AR1000%20UK.html 

Mike,

Hi,

Sorry, you are absolutely correct for type USB type C connections.  Given that type C leads are identical both ends, there has to be a means of preventing someone connecting two power sources together and the CC pin(s) are used to ensure that power is not delivered unless a sink is attached (amongst other things).

Having said that, I wouldn't be relying on that control for safety purposes although it might affect the results of the experiment.  It might be especially relevant if the absence of the pull down on actually turns off the charger as an energy saving feature.