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An electrical experiment for Easter

Chris Pearson

If I have missed something, please let me know.

Introduction

Electrocution has been reported due to the use of a mobile phone in a bath whilst it is plugged into a charger (https://www.rte.ie/news/2025/1001/1536213-inquest-anne-marie-ogorman/). The aim of this study was to establish whether the output of a mobile phone charger can present a risk to the user.

Method

A 5% solution of sodium chloride was placed in stainless steel bowl. The bowl was connected to the earth pin of a twin BS 1363 socket-outlet via an ammeter with a 10 mA full-scale deflection (Avometer Eight Mk 6). 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.

Discussion

These findings do not confirm the hypothesis that the use of a mobile phone which is connected to a charger whilst taking a bath gives rise to a risk of an electric shock. It may be that the risk exists only if the individual is in contact with the charger itself, or the charger becomes immersed. Further work is required to investigate this alternative hypothesis.

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

    Those from leading brands that provide mobile phones are unlikely to have such 'obvious(?)' galvanic failure modes.

    Other fault conditions are possible. It's easy to blame the wrong end of the stick when poking it in a socket. (I remember a historical incident with live Christmas Lights and child standing on bare radiator pipes to reach the tree, and 'blaming' the fault on the radiator pipes now being earthed)

  • A couple of thoughts ... could the charger have been exposed to high humidity leading to condensation forming inside? (insufficient creepage/clearance distances)

    Also as water (even salty water) isn't a great conductor the limited c.s.a of USB C contact was mean some considerable extra resistance - compared with a phone-sized electrode for instance (if perhaps one pole of the charge supply is connected to "chassis").

    (Was the AVO on a d.c. or a.c. setting?)

      - Andy.

  • Chris Pearson said:
    These findings do not confirm the hypothesis that the use of a mobile phone which is connected to a charger whilst taking a bath gives rise to a risk of an electric shock.

    Only for the particular charger you conducted the experiment using and under the particular environmental conditions.

    How do we know an after-market charger wasn't being used?

    I'd perhaps be looking there, although I don't believe all OEM models are the same either - certainly lots of discussion about some designs, for example: discussions.apple.com/.../250613526

  • in reply to AJJewsbury
    AJJewsbury said:
    Was the AVO on a d.c. or a.c. setting?

    Both were used - not a flicker either way.

  • in reply to gkenyon
    gkenyon said:
    Only for the particular charger you conducted the experiment using and under the particular environmental conditions.

    I agree that experiments where N = 1 should be interpreted with caution, but the the report on the Irish case said, "Mr Collins said he had found no fault with either the phone, the charger or the cable ...".

    I imagine that just about every household in the land has at least one mains extension lead. Long USB cables are available, but I cannot help feeling that the mains extension lead became immersed.

    That could be my next experiment.

  • I had a go at finding an actual report form the Coroner's Court but couldn't find it. Various media articles refer to the Consultant forensic engineer stating that the charger gave 2 amps, which seems an odd thing for them to say (since presumably that's 2 amps at 5V)? I'd have thought what would be more relevant would be the leakage capacitance across the convertor which may cause the DC output to be something like 115V ac to ground (if it's symmetrical from both L and N to the output) with a source impedance that will allow a few milliamps to flow - I've seen that happen quite commonly.

    The trouble is there's a number of stages of interpretation going on here - the husband (who of course I do feel sympathy for) interpreting the consulting engineer's report, and the journalists then interpreting that. It would be interesting to find out what the Consultant forensic engineer actually said.

  • in reply to Andy Millar
    Andy Millar said:
    I had a go at finding an actual report form the Coroner's Court but couldn't find it.

    I believe it can be requested if one had a good reason for doing so.

  • in reply to gkenyon

    Yes, I'm sure it can be, unfortunately the only reason I could give would be "morbid engineering curiosity"!

  • in reply to Andy Millar
    Andy Millar said:
    I had a go at finding an actual report form the Coroner's Court but couldn't find it.

    That was one of the first things that I did too.

    As a general rule, Court and Tribunal hearings in England and Wales are open to the public: the law is not only done, but seen to be done. I think that a report is issued only in a minority of cases. Otherwise, there is not much more than a death certificate stating who the deceased was and how, when and where they died. I suspect that similar rules apply in Eire.

    Andy Millar said:
    presumably that's 2 amps at 5V

    My A1696 charger specifies 5V [symbol for smooth or pulsed DC] 3A or 9V/2A. Model A1299 specifies 5V/1A and A1357 is 5.1V/2.1A. The first two are designed for BS 1363 socket outlets, so they have an earth pin, but I suspect it is only there to open the shutter. The third one is a world travel adapter kit. There is a convertor and six different plugs. It is clear that the earth pin on the BS 1363 part is connected to nothing.

  • in reply to Chris Pearson
    Chris Pearson said:
    so they have an earth pin, but I suspect it is only there to open the shutter.

    I'd expect, given some reports of an expected tingle from the phone case while being charged, is that the Apple design does include an RF filter, reference to the expected Earth connections (as is normal for RF / EMI filters).

    These RF filters deliver half supply voltage, via the Y-capacitor divider, to the earth connection. It's that half supply voltage that delivers the tingle when you are the earth. If the Y-suppression capacitor has a fault, then it can deliver even more...

    --

    I also suspect that the 2A in the newspaper report is a red-herring that is actually a reference to the output current capacity of the USB C standard, albeit at a low voltage. 

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