An electrical experiment for Easter

Philip Oakley said:

the Apple design does include an RF filter

When it comes to electronics, my eyes glaze over, but the charger says (in such teeny tiny writing that I had to use a pair of loupes) "EMC 3258".

I was thinking further about whether manufacturers should give warnings. Generally, I view these things along the lines of a cooker having a warning which says "may get hot". May or will?

In the box of my iPhone, purchased about 13 months ago, are some leaflets in various tongues, whose wring is so small that i could barely read it. They say, "For information about charging, see "important safety information" in the iPhone User Guide."

So, how do you read the guide before you have charged the phone?

Having charged the phone by whatever means, you go online.

Philip Oakley said:

Cheap replacement chargers are the most suspicious for needing a test.

It says, "You can also charge iPhone with “Made for iPhone” or other third-party cables and power adapters that are compliant with USB 2.0 or later and with applicable country regulations and international and regional safety standards. Other adapters may not meet applicable safety standards, and charging with such adapters could pose a risk of death or injury."

And later on, "Donʼt use the power adapter in wet locations, such as near a sink, bathtub, or shower stall, and don’t connect or disconnect the power adapter with wet hands."

There's your warning, and it might get Apple off the hook in a court, but is it enough? You tell me.

As Phil Oakley says some chargers give a significant bite from the metal outer of a USB plug due to the capacitor which us connected across the output transformer older supply's were more bighty than newer ones BUT if the socket the charger was plugged into was wired the wrong way round it mite still prove to be a hazard. 

if the socket the charger was plugged into was wired the wrong way round it mite still prove to be a hazard. 

L-N reversal hopefully shouldn't be an issue - since much of the world has unpolarized sockets (pretty much all of Europe), Japan etc. the designs can't presume either of the live pins is "safe". L-PE reversal could be a big issue ... if the USB chargers used the PE connection - none of the ones I've looked at seem to. (which probably makes sense as you wouldn't want earth loops with an interconnected group of USB connected items).

  - Andy.

Agreed. In my world travel adapter kit, four of the six plugs can be inserted either way round.

Looking through the quotes from the expert witness,  consultant forensic engineer Paul Collins, and some of the other things he said about Europe not permitting mains sockets in bathrooms (nearly all Euroland countries  very much do actually) and how much current you need to hurt someone, I'd suggest that while he is presumably an expert on forensic techniques and identifying the causes of death, it is quite reasonable that the finer details of electrical practice for fixed wiring might not be his forte.

The general advice he is quoted as giving however, to let it charge on the dressing table, not in the bathroom, is absolutely sensible.

Other cases he has handled include this tragic one, (https://www.donegallive.ie/news/local-news/784076/inquest-warning-about-electric-heaters-after-death-of-woman-in-house-fire.html)

and suggest he has a far more general scope than electrocution.

I suppose what I'm saying is the 2A figure is probably a bit of a red herring.

Mike.

AJJewsbury said:

L-N reversal hopefully shouldn't be an issue - since much of the world has unpolarized sockets (pretty much all of Europe), Japan etc. the designs can't presume either of the live pins is "safe".

It shouldn't be, but it inevitably is in certain fault conditions in a product, especially for devices with wired Ethernet connections and similar, as there has to be a discharge path back to 'earth' somehow. It's also worth noting that more and more switching converter products are becoming 'transformerless' because this is now permitted in the product standard.

Now, if you select a couple of large enough impedances in series then, at least for dry conditions, something connected directly to the mains still isn't a problem ... but in certain conditions It can be. It's notable that it was not permissible to use what BS 7671/Wiring Regulations used to call the 'protective measure of limitation of discharge of energy' in certain special locations ... like bathrooms.

So, yes, don't use your phone in the bath while it's on charge (and definitely not when it's on charge from the mains).

Chris Pearson said:

There's your warning, and it might get Apple off the hook in a court, but is it enough? You tell me.

When I'm advising clients about hazard mitigation, for a start putting anything in the manual is a last resort (since we know hardly anyone reads them), but if you do need to then it only really works if it's right next to something they will need to read to make the whatever-it-is work. Grouping 50 safety instructions in the front of the manual, which most manufacturers do, is actually the worst pace to put them. (One or two big ones might be ok there.) 

Frankly, I think safety warnings in manuals where we know the user is not going to read those manuals - i.e. where we know they can work out for themselves how to use the device - are not credible mitigations for hazards.

Personally I don't know of any test cases for this (I probably should), but I would expect that if "the man on the Clapham omnibus" thought something was a reasonable action to take with a device, then writing in the manual that they mustn't do that would probably not constitute a reasonably practicable measure in law. Basically, I think it's unlikely to be a defence. Even if you print on the manual (as everyone does) "Important read this first".

This particular case would make an interesting test case though, as it's slightly new territory. I think if it had been, say, a mains powered radio a court would determine that the average person could be expected to know not to take that in the bath with them. But we are used to taking USB powered devices into a wider range of locations. That's the challenge with the law in this area, it's all down to what a court decides is "reasonable".

It's why I'm very glad I've never worked with domestic equipment, with "professional" equipment we can make slightly more reasoned assumptions about how the users should behave (and e.g. what they should be expected to read and follow). Not that they always do, and we still have to take that knowledge into account.

Andy Millar said:

Frankly, I think safety warnings in manuals where we know the user is not going to read those manuals - i.e. where we know they can work out for themselves how to use the device - are not credible mitigations for hazards.

Agreed. I think in answer to my own question, no it is not enough.

Andy Millar said:

the man on the Clapham omnibus

He is on his Easter holiday today, but his good friend, "the officious bystander" insisted on the warning.

There may be no caselaw because of consumer protection statutes.

R.7(2) of the General Product Safety Regulations 2005 says, "The presence of warnings does not exempt any person from compliance with the other requirements of these Regulations."

R2 (Interpretation) says, " “safe product” means a product which, under normal or reasonably foreseeable conditions of use ... does not present any risk [etc.]".

My personal view is that plugging in a USB cable when in a bath is foreseeable.

On the face of it, my experiment shows that I could do that safely with my equipment under my conditions (as GK pointed out). However, what if your charger were faulty and you suffered serious harm? I don't think that the warning would make a scrap of difference because the product is plainly not safe. Had you received a mild shock because you were sitting at your desk, the charger still would not have been safe.

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.