Couple,
I’m in a plastic bath and there’s a radio next to me, the radio falls into the bath…
Will I be electrocuted?
Electrocution can happen as follows:
– Power goes from the line, through the person to the ground.
– Current goes from the line, through the person to the neuter (or other phase).
I think I am completely isolated from the earth in the bath. So electrocution through earth cannot occur. I can accidentally touch the water pipe or drain, and they are grounded = electrocution.
The radio falling into the water will cause a short circuit internally in the device, since the water mixture of soap and dirt will conduct. But the current follows the shortest path through the water, so why should the current go around your body? (Counted that the radio is not between your legs or something).
I once saw an episode of Mythbusters where they tested this, but I thought they didn’t actually perform their test well (eg in a metal bath).
Answer
Dear Peter
You are right in your premise: electrocution can only occur in the 2 cases you describe. Then why is it so dangerous? You actually mention it yourself: “calculated that the radio is not between your legs or something”. The moment a device is in the water, what happens?
The device you are talking about (radio, hair dryer) is usually double insulated. This means that there is no earth connection on the device. If you are in a condition isolated from earth, the RCD will not be able to do its job as there is no loss (current) to earth. The voltage thus remains (for the time being) on ​​the device.
So current will flow from one line wire to the other line wire (or neutral). You are partially correct that the current will choose the shortest path (path of least resistance). However, it is not the case that because there is a slightly more favorable (lower impedance) path directly between the two line wires, no current can flow through your body! Basically we are not talking about a choice of the two paths here, the flow will simply take both paths. Compare it to a parallel connection of resistors. The voltage across the two resistors is the same, so even though one resistor is smaller than the other, a current will still flow through the larger resistor! (luckily, otherwise we could only use 1 device at a time!)
It obviously becomes more dangerous the closer you get to the device.
The water tap or drain may be grounded, creating a potential flow path to ground. This creates additional risk, but also offers the chance that a RCD does its job.
Hopefully it makes this a little clearer for you.
For your information:
You feel the current from about 1.5 mA. The first cramps come from about 8 mA and the current that causes a general (deadly) cramp is only 15 mA, which is less than the current at which the RCD will operate!
Conclusion: electricity and water: keep far from each other!
Answered by
ing. Filip Declercq
Home automation, embedded systems, microcontrollers, windows applications, bluetooth, usb, healthcare & technology
Doorniksesteenweg 145 8500 Kortrijk
http://www.vives.be
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