# 120 volts can kill you

## Is it the current that kills you, not the voltage?

No, this is a misleading simplification. People are very resilient. Without high voltage can not Electricity flowing through a person to power them.

It's not the voltage or the current that kills you; It's the energy.

However, if you rub your feet across a carpet on a dry day, you will become charged Thousands of volts on . If you then touch a grounded metal object, the discharge can several amps of electricity send through your body:

about 5 to 7 kilovolts was the maximum value measured on humans. ... asked him to shuffle his feet while connected to the electrostatic voltmeter. Much to the surprise of the EMC laboratory, the voltmeter registered 18000 volts ! A Brief History of Electrostatic Discharge Testing for Electronic Products

It should be mentioned that the reference model of the ESD waveform is the human-metal discharge. ... The maximum ESD current value is 12 A while the IEC standard 15 A Are defined. Electrostatic discharge current linear approach and circuit design method

This is far more than 25 V and 70 mA. So if these can each kill you, why not ESD? Because the duration of the discharge is a fraction of a microsecond and the total energy release is only a few millijoules. It doesn't have enough time to cause fibrillation or heat and burn significant amounts of tissue.

"The effects of electrical current flowing through the human body are discussed in detail in the International Electro Technical Commission document IEC 479-2: 1987. This document indicates that a transient or capacitive discharge, as is the case with static electricity is the case, energy is required over 5 joules (5000 mJ) to create a direct serious health risk. "- Static electricity in modern buildings

The reason this "safety tip" is terrible is because it misleads people into thinking that high current sources are dangerous to touch and high voltage sources are not.

Most power sources are voltage sources, not current sources. This means that they output a constant voltage and the current in the circuit depends on the resistance of the load (in this case, the human body). This applies to power lines, batteries, etc. Most people fail to understand that the current indicated on a power adapter is only a maximum rating and will not flow through their body when they are touched.

If you connect a 1 kΩ resistor to a 12 V supply, the same 12 mA current will flow regardless of whether the supply reads 100 mA or 100 A. The amperage of a power supply unit only indicates the current that it delivers when connected to a could small enough resistance. It doesn't force that amount of electricity through anything it touches, or it would keep flowing through the air.

Yes, car batteries can deliver a lot of current (hundreds of amps) but it only does so when connected through a small resistor. If you connect a screwdriver to the terminals, a large current will flow and the screwdriver will melt, the battery will explode, etc. If you put your hands over the terminals, nothing will happen. This is because the resistance of your skin is much higher than the resistance of the screwdriver. The 12 V 600 A car battery will not do you any harm because the voltage is not high enough.

### peterG

Exactly right, with the exception of "several amps of current" - even at the time of connection, the instantaneous current would only be 200 mA with a static charge of 20 kV and a body resistance of 100 K. . and that is in the artificial case where there is no other resistance.

### Endolite

@peterG, that's a link to the source of this instruction. "relatively high current that can consume several amps in a fraction of a microsecond". Remember that body resistance is non-linear and varies with tension. The internal body resistance can be up to 300 ohms.

### peterG

I read the link and there I got the 20kV. But I got trapped in finding the idea of ​​multiple amps - even for that tiny moment at the top of the curve - so counter-intuitive that I thought it couldn't possibly be right. But yes, if we define 'several' = 2 then 20 kV would require a body resistance of 10 k, which is not at all unlikely. So I can only question the model - can we really model this as 300pF at 20kV discharge over 10,000k, or is that an over-simplification?

### Endolite

@peterG: Yeah, it's not intuitive which is the point of my answer: it's not the electricity or the voltage. It's the energy and whether it's enough energy to destroy tissues or stop your heart. I don't know what the right model for the human body is, but at high voltages, insulators break down and their resistance drops sharply.

### Endolite

@coleopterist Yes it is the area under the V * I curve. Volts × amps × second = joules. The safety tip should read: "Make sure that your body is away from sources of high voltage and that there are no metal objects near sources of high current."