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There lots of people claiming that 240VAC is much more dangerous than 110VAC. Some even find it insane to have 240VAC. I think this claim comes mainly from the fact that 240V will draw twice the current through a same resistor and that's what will kill you.

There is also a claim that electrical body resistance is much lower on 240V when compared with 110V

I find this rather laughable since as we all know it isn't voltage that kills you but the current. In the first split second that you come in contact with electricity 240V will give you twice the current of 110V, but I am convinced that what really does kill you is time because once your skin starts to burn the electrical resistance of your skin drops very low that it doesn't really matter anymore if it's 240 or 110.

Personally I find 110V more dangerous and the main reason is that you need bigger currents for the same appliance which in return considerably highers Joule heating, you get bigger wearing on sockets/switches and it could actually burn down the whole place.

So what is more Dangerous : 110V or 240V?

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    \$\begingroup\$ Technically the energy is what kills you. And the human body cannot be modeled as a simple resistor. The human body's resistance is a function of applied voltage. So for 220 volts the body's resistance is lower than in the case of 110v. In any case both are dangerous. \$\endgroup\$ – Mike Nov 3 '14 at 10:39
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    \$\begingroup\$ youtube.com/watch?v=snk3C4m44SY \$\endgroup\$ – JonRB Nov 3 '14 at 10:41
  • \$\begingroup\$ A very interesting read: brighthubengineering.com/power-plants/… \$\endgroup\$ – Majenko Nov 3 '14 at 10:50
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One reason AC is more deadly is that any path which cause the current to pass through the body and cross the heart, e.g. left-hand-to-right-hand or hand-to-foot will cause the heart to attempt to synchronize its beat to 60 Hz. The heart goes into fibrillation, and unless someone gets an AED on you within a couple minutes, that's the end. In addition, the alternating current locks the muscles in a spasm, so you can't pull away. With DC, your greatest danger is burns. The reason DC feels much worse is that it causes the muscles to contract abruptly (whereas AC causes them to lock), so the physical effect is more painful. Edison favored DC, and Westinghouse favored AC. Edison wanted to introduce the word "Westinghoused" as a synonym for "electrocuted".

A higher voltage breaks down a poor insulator (e.g., the thin layer of nonconductive dry skin that covers the body), and once that insulator breaks down, the inner layers of the skin, and the muscles, are highly conductive.

15 mA is the lethal dose. That is why GFIs are set to trigger at a current of 5 mA differential.

I have not tried the experiment, but I have read that a 9 V battery connected to two sharp needles will, if the needles are stuck into the skin, be very painful.

I have had several EMG tests, which measure neural delays. For example, they are very good at telling the difference between neuropathy of the hand (normal neural transmission from the area of the elbow and the fingertip) and Carpal Tunnel Syndrome (significant neural delays). This is done by putting a wire on one finger, and hitting me with a cattle prod. My arm jumps, the experience is painful (I once asked the technician if Amnesty International knew about him; sometimes toward the end I will tell the tech that if I knew any secrets, I'd be telling him). Each pulse is at a higher voltage; he hits me with the cattle prod, takes it away, clicks a knob, and repeats. I looked at the calibration once; the knob was set to 800 V after the last test.

In one of the more surreal experiences, and this is over 50 years ago, I was helping the electrician at the company I worked at. He used a wooden ladder, always. He was up amongst the many panels; we had 120, 240, 440, and 880 volts in that array. So he calls down to me to get his voltmeter, which is down the hall. I come back with it, and he says, "Never mind, this is the 440 line". After he came down, he explained that he just bridged two of the phases with his fingers. "It was too strong to be 220, and too weak to be 880". This was a guy who had a perfect way to locate a short. Remember, this is 50 years ago, and you couldn't buy a TDR at Wal-Mart. He'd disconnect everything from the circuit, then run a cable from the 1600 V line down to the wire whose circuit was shorted (the end disconnected from the 120 V or 240 V panel). WHAM! Wherever the short was, there was an explosion. 1600 V at about 800 A, if I recall correctly.

I have been hit by 120 VAC, and a variety of DC voltages from 90 to 20,000 V. Even the low DC voltages (remember when electronics had these weird hot glass bottles plugged in? One of the voltages, called B+, ran from about 200 VDC to 800 VDC). I quickly learned the trick of shorting the power supply condensers (now known as capacitors) because that voltage stuck around for a very long time after the device was turned off and unplugged. The DC hits were memorably painful. The AC hits were far more dangerous.

A gun is always loaded, so the rule of "never point a loaded gun at something you don't plan to shoot" means "never point any weapon at something you don't plan to shoot". Well, I was taught "A circuit is always live". So never do anything that might create a path between that wire and ground, especially if that path involves your body. One day, about 30 years ago, I replaced a porch light. I had tripped the breaker on that circuit. I took the old fixture off, put the new fixture on, screwed in the bulb, and it lit. Oops. I guess the training of my youth paid off.

Higher voltages are more dangerous because they break down poor dielectrics faster. Remember, at all times, 15 mA across the heart is all it takes.

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    \$\begingroup\$ This is a very entertaining post. \$\endgroup\$ – mkeith Nov 6 '14 at 5:09
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    \$\begingroup\$ "In addition, the alternating current locks the muscles in a spasm, so you can't pull away. With DC, your greatest danger is burns. The reason DC feels much worse is that it causes the muscles to contract abruptly (whereas AC causes them to lock)" - isn't it the other way around? \$\endgroup\$ – cantsay Apr 19 '16 at 1:34
  • \$\begingroup\$ @cantsay AC stands for alternating current; thus your muscles will contract then relax over and over in quick succession locking your muscles in place. DC stands for direct current so the electricity only flows in one direction contracting your muscles, and is why people tell you to test an electric fence with the back of your hand. \$\endgroup\$ – rom016 Sep 25 '16 at 12:25
  • \$\begingroup\$ 1600V at 800A will handily take care of most shorts, although I question that electricians sanity. 0o \$\endgroup\$ – CHendrix Dec 1 '16 at 12:03
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    \$\begingroup\$ RE: "I have not tried the experiment, but I have read that a 9 V battery connected to two sharp needles will, if the needles are stuck into the skin, be very painful." - Sharp needles penetrating your skin will likely be the main source of pain. You can simply lick 9V battery with your tongue to know the experience. It is quite unpleasant but far from "very painful". \$\endgroup\$ – Alex Nov 29 '18 at 2:07
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its the difference between dead and really dead & more todo with the installation (RCCB's limited supply etc...)

Both are dangerous and a healthy fear of electricity is good. From a UK point of view that then influenced the EU, there is a LowVoltageDirective

The directive covers electrical equipment with a voltage at input or output terminals between 50 and 1000 volts for alternating current (AC) or between 75 and 1500 volts for direct current (DC). Importantly, it does not cover voltages within equipment[1] The directive does not cover components (broadly, this refers to individual electronic components).

Basically ExtraLowVoltage being upto 75Vdc or 50Vac & this is "safe"

The Electrical Equipment (Safety) Regulations 1994" Low Voltage Directive (LVD) 2006/95/EC

I have been hit by 110Vac, 230Vac, 270Vdc, 540Vdc and all I can tell you is neither is pleasant but the DC potentials were a lot worse.

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  • \$\begingroup\$ That's interesting, I've found that AC was worse than DC in that the same effects arise at lower currents (source in my answer here: electronics.stackexchange.com/questions/129302/…). Could you describe the difference you felt between the two? Feel free to help me improve my answer quoted above, too. \$\endgroup\$ – Mister Mystère Nov 3 '14 at 10:45
  • \$\begingroup\$ When trying to describe DC vs AC shock, I would say the pain from DC feels more like coming from inside of your body like huge painful cramps while AC is more like painful vibrations. \$\endgroup\$ – Daniel P Nov 3 '14 at 11:15
  • \$\begingroup\$ +1 for personal experience. Maybe we should open a pool or something similar with everyone's "shocking" experiences. On topic: the cramping of your hands muscles could make you "hold onto" an AC source, as far as I know this phenomena does not happen with DC. Because of this, touching potentially live stuff with the outside of your palm/hand is a "good" idea(not that it is a good idea, but it is better). \$\endgroup\$ – WalyKu Nov 3 '14 at 13:23
  • \$\begingroup\$ AC will freeze your muscle while DC will contract them. So if you really take a wire in your hand DC will make you hold it even stronger while AC will just "freeze" your muscle. \$\endgroup\$ – Daniel P Nov 3 '14 at 14:16
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This is an esoteric answer, because others have answered your question as it's phrased. On the same circuit layout, 240V is worse than 110V. But when does this not apply? (Side note, the UK/Europe uses 230V as house wiring, lower losses etc.)

If you start taking things into account like wiring, and transformers, this all gets a little tricky. When you accidentally short something, the "source impedance" comes into play, that is, the voltage drop across the wiring, and the power sources characteristics.

One such example - you are working on a ship that has a 300 kVA (or 300kW) generator, putting out 600V. That is transformed down to 240V and 110V. Which one is more deadly now?

The power output is fixed, so assuming the wiring is all the same, the 110V circuit is capable of putting out twice the current. ( P = I V, if P is fixed, double the V halves the I ).

Second example - you have a 1kW heater connected to 240V or 110V, with the wire sized appropriately for the current (both have same source impedance prior to the wire). Which is worse now?

Well, the circuit impedance is much higher on the 240V circuit, potentially enough to result in it supplying less than the 110V circuit once the ends are bridged. The 240V heater requires much less current nominally because the voltage is higher, so it can use much thinner wire.

Basically anything over 55Vac is bad news, and once you get to the magic current number across your heart, it doesn't get any worse for you until burning occurs. There are all kinds of other factors to consider, such as the full circuits resistance, current path through the body, and reactance of the lines (you don't want this one explaining).

Finally - at any voltage DC is much worse than AC in practice. This is because DC is much harder to interrupt. The zero crossing of the waveform helps quench the arc from whatever interrupting circuit you are using, so in practice AC circuits are way safer to work with than DC if the voltage is at any level.

(p.s. I'm an Electrical Engineer who happily works with 600V+ power circuit panels without a second thought, but a 12V car battery scares me).

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Its current that kills, and it kills because it shuts down your heart\brain first. One can get electrical burns from heating but you'd have to hold on to that wire for a long time or have lots of voltage.

From the NIH Conduction of Electrical Current to and Through the Human Body: A Review

+=========================================+===============================================+
| Estimated effects of 60 Hz AC currents* |                                               |
+=========================================+===============================================+
| 1 mA                                    | Barely perceptible                            |
+-----------------------------------------+-----------------------------------------------+
| 16 mA                                   | Max current an avg man can grasp and “let go” |
+-----------------------------------------+-----------------------------------------------+
| 20 mA                                   | Paralysis of respiratory muscles              |
+-----------------------------------------+-----------------------------------------------+
| 100 mA                                  | Ventricular fibrillation threshold            |
+-----------------------------------------+-----------------------------------------------+
| 2 A                                     | Cardiac standstill and internal organ damage  |
+-----------------------------------------+-----------------------------------------------+
| 15/20 A                                 | Common fuse breaker opens circuit†            |
+-----------------------------------------+-----------------------------------------------+

Voltage can be thought of as the force that pushes electric current through the body. Depending on the resistance, a certain amount of current will flow for any given voltage. It is the current that determines physiological effects. Nevertheless, voltage does influence the outcome of an electric shock in a number of ways, as discussed below.

The current is determined by the resistance from the skin, you can kind of determine this yourself by holding a multimeter (although you will get some contact resistance that you'd have to account for from the boundary between the contacts and the skin). The resistance of the skin differs from person to person.

The body has resistance to current flow. More than 99% of the body's resistance to electric current flow is at the skin. Resistance is measured in ohms. A calloused, dry hand may have more than 100,000 Ω because of a thick outer layer of dead cells in the stratum corneum. The internal body resistance is about 300 Ω, being related to the wet, relatively salty tissues beneath the skin. The skin resistance can be effectively bypassed if there is skin breakdown from high voltage, a cut, a deep abrasion, or immersion in water (Table ​(Table2).2). The skin acts like an electrical device such as a capacitor in that it allows more current to flow if a voltage is changing rapidly. A rapidly changing voltage will be applied to the palm and fingers of one's hand if it is holding a metal tool that suddenly touches a voltage source. This type of contact will give a much greater current amplitude in the body than would otherwise occur.2

At the end of the day if someone has the same resistance, doubling the voltage will double the current and be more likely to kill you. So 240V is more dangerous than 120V.

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Here's how I always counter those arguments.

"The quality of the death you experience with 240V is likely worse than the quality of death you experience with 120V. But since the end result is the same, we may never know for sure."

The point is, NEITHER of them are "safe" and "safer" is a pointless argument to make about something that is potentially lethal either way.

That said, I have been shocked by 120V, 240V, and 480V. I can attest to the fact that they ALL hurt like hell, but (as far as I know*) none of them were lethal!

*Unless of course I am dead and have just not realized that yet, because I have no time for that nonsense...

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