How can a mobile phone being charged kill by electrocution?

Question

We have in France a wave of warnings about using a mobile phone while being charged in humid environments (or when taking a bath).

A charger is plugged directly into the wall socket and the charge voltage is low. I can imagine that with some "shady" chargers and condensation, a bridge between the high and low voltage could be created in the right conditions.

Is this what the warning is actually about?

EDIT: the answers are very interesting so far - I just wanted to highlight the fact that I am not challenging the warning (or any warning about electricity + water), I am interested in the technical ways the shock may happen (which is well explained in the answers)

Answer 1

Yes, a shady charger with inadequate isolation (creepage) or possibly even conductive debris inside (see both). Possibly transformers made badly (eg. with magnet wire rather than triple-insulated wire).

Or water (or a very rare fault) in a better made charger. They're typically not sealed against water ingress through the USB socket. And water leakage can lead to carbon tracking which can allow a lot (ie. fatal amount) of current to flow.

There was a case a few years ago of a girl who died because she had her bare foot on a water pipe at an internet cafe (if memory serves) and the current went from the faulty charger through her heart to the pipe.

Basically I would not use anything that is plugged into the mains in the tub, no matter the product. The pump in our tub should be properly grounded for safety and nothing else gets close.

If your battery is getting low and you must use it, plug it into a power bank (that is not connected to anything else) and charge it from there.

GFCI/RCD outlets usually required in bathrooms should save you, but extension cords also exist, and better not to test such things.

Answer 2

The problem is with cheap chargers that are not isolated. One or the other pole of the charger has a straight through connection to the wires in the outlet. That is to say, one of the wires on the low voltage side is connected straight to the pins in the outlet.

If you use a non-isolated charger and that straight through connection is connected to the live wire in the outlet, then you can get a shock by touching that wire of the charger. If you are really unlucky, the hot wire will be connected to the metal housing of the phone.

If you are in a wet or really humid place, that hot wire can give you a fatal shock.

The real problem comes from cheap chargers (and counterfeit chargers) rather than chargers from good manufacturers. A real Apple charger will be properly made - it would have to be severely (and obviously) damaged to be hazardous. A fake Apple charger might be sold at (or near) the same price, but may be improperly built - it is a hazard when new.

The same goes for other manufacturers. The cheap chargers you can buy in low price junk stores can be dangerous. The brand name chargers you buy in better stores will usually be properly made.

The warnings tell you to be careful with all chargers because it's tough to teach people how to tell cheap, dangerous junk from good quality equipment.

---

Even a good quality charger can give you a fatal shock if it is plugged in and you drop it in the water while you are in the tub.

Answer 3

Although these have double insulation (Plastic case and varnish insulated magnet wire in transformer) , dust and humidity or soldering flux contamination with dust, humidity and can reduce this magnetic wire insulation by up to a factor of 10 and then a line impulse spike can breakdown that insulation barrier now passing low impedance from the line input to the DC output. So it is wise not to use a charger in the tub. A Ground Fault Current Interrupter (GFCI) socket is a life-saving device should be used which detects if there is any external current being drawn unbalancing the supply and return current.

In North America some GFCI's are more sensitive (5mA) than some 10mA RCD tripping Differential RCD breakers ( often used in EU) and these GFCI's work with DC/AC,and other AC freq leakage but do not include current limiting breakers. Those are on the remote panel. The ones on the panel may be used in N.A. but are more $$.

Each grounded SMPS type device is permitted 2.5mA leakage but Y filter cap currents are usually designed for 1mA

ref

Answer 4

And some will be using an extension lead with the charger plugged into that.

Then the whole thing falls in the bath.

Answer 5

If you have a properly designed charger plugged in correctly, you still run the risk that transient conditions on the electric line can push through. In particular, lightning can travel through your house or its wiring or plumbing, overcoming most reasonable attempts at insulation and isolation.