paddingtongreen

Whether wet or dry the body has a resistance to the flow of electricity.

Current = Voltage/Resistance.

This guy tested his resistance to 1,000,000 Ohms. Use 1,200,00 for simplicity.

With V=240, you get 240/1,200,00= 0.2mA through you.

With V=120, you get 120/1,200,00=0.1mA through you.

One mA is one thousandth of an amp.

QED, more voltage, bigger shock.

p.s. Those currents look low to me, you would barely feel them, but the proportions hold good.

fatbrit

It's volts that jolt but mills (as in milliamperes) that kill!

I'm with Catman on this.

paddingtongreen

Correct. But for a given resistance, the more jolt, the more mills; less jolt, less mills.

You can touch a pair of wires that have a huge current available, but if the voltage is low, you won't feel it.

fatbrit

e.g. your car battery.

chartreuse

What I've been trying to explain to Steerpike is, while Ohm's law may be linear, getting electrocuted to death isn't. First off, the body's resistance varies according to where you measure it, as well as due to environmental conditions. Secondly, while a current of between 100mA and 200mA will reliably cause v-fib, and death, currents over 200mA can cause muscle contractions so severe that the heart clamps shut and v-fib is prevented, allowing for resuscitation.

So, practically, there are so many variables that the only voltage worth worrying about is 30V, the PD at which a current can most likely get flowing in the first place.

ETA: This is all AC. DC is different.

helwardman

Talking about the resistance of your body when considering AC is inconsequential as it is the impedance that should be considered.

In one of my former jobs, I was once man-handling a 230V mains transformer out of a power supply prior to fitting a replacement. In my youthful haste, I had failed to disconnect the supply and I received a shock along both arms and across my chest which lasted for a number of seconds. I felt a bit ill for a few minutes afterwards, but it certainly didn't kill me. A similar shock applied to a number of different people may well have killed someone. Differences in body impedance determine the amount of current flowing in each case.

I would always rather be shocked by a 120V supply than a 230V supply. I would never want to receive a shock from a DC source of greater than about 20V as DC can be particularly lethal.

NB: The UK supply voltage was harmonised with the rest of Europe some years ago and is now officially 230V +/- 10%. It might measure 240V at some locations but it is not a 240V supply.

Steerpike

So my question from above still stands ... I can touch 240V AC and 120V AC with dry skin and when well-insulated to ground, and it won't do me much harm. Conversely, I can touch 240V AC and 120V AC with wet skin, and when 'grounded' (eg, hairdryer in bathtub, etc) and die. Would you agree with that so far?

Assuming you agree, then I would say it's logical you are more likely to survive the intervening conditions (damp skin, moderate grounding) with 120 V than with 240V, because with 240 V you are statistically more likely to encounter the required current flow that can kill you. I mean, testing this would be impossible but if you could theoretically determine the conditions that would kill you, then gradually increase the resistance (or impedance ) to ground of the subject, you would reduce the current to the point below that required to kill - this threshold would be crossed more quickly at 120V than at 240V.

SDDep

Just dont pull the plug...

chartreuse

No. As I've explained, there are too many variables to draw such a simplistic conclusion.

Here's an equally simplistic falsification of your hypothesis. There's a "death window" between 100 and 200mA. For certain values of bodily resistance (as you note, we're using the term as shorthand for impedance) a voltage of 120 will cause a current in that range, leading to death, while a voltage of 240 will cause a current over 200mA, allowing for resuscitation. This is an oversimplification, but it's an example of a scenario when you'd rather get a belt from 240V than 120V.

CitySimon

Screw it, just pull the plug out.

MsElui

that's ok if the one youve tripped is the one with the reset button on it. In my house (which is newly built) several GFI sockets work off one circuit and only one socket has the reset button so you have to go looking. and we have 2 circuits like that.