Is It The Voltage Or The Current Which Kills?

Is it the current or the voltage that kills from a deadly electric shock?

It s a long disputed question which many people don t understand fully. Some think it s the voltage, while others think it s the current. But when asked why, not many people would be able to explain what the significance of what a high current or a high voltage actually implies.

What actually is current?

Current is simply defined as the rate of flow of charge (usually electrons) in a conductor. Increasing the current across a light bulb or an LED will cause it to shine brighter. Increasing the current across a heating element will cause it to get hotter. It is the current that governs how intensely an active component can function.

If the current flowing through a component is too large, it can cause damage. For example, imagine turning up the current so high across a light bulb that it shines too brightly and blows. The human body is very fragile when it comes to electric shocks, especially the heart. It turns out that a current of only 20 milliamps (that s 0.02A) passing through the entire body into the heart is enough to kill someone.

And what actually is voltage?

It is the voltage which causes current to flow through a circuit. It is a measure of the amount of energy that each of the charge carriers (usually electrons) in a circuit have. Think of it as the amount of kick that the power supply in the circuit can provide. The higher the voltage in an electric pulse, the more easily the current can pass through a component in the circuit.

Ohm s Law

One of the most important equations governing electronics is Ohm s law. It s a simple linear equation which relates the amount of current flowing through a component with the resistance of that component and the voltage of the power source. It is written as V = IR, where V is the voltage, I is the current, and R is the resistance. By dividing through by R, we obtain I = V/R. We can see that if we want to keep our current constant, we need to keep the fraction on the right hand side of the equation constant. So the higher the resistance of the component, the higher the voltage of the power source has to be to compensate.

This is the idea behind passing electricity through objects with a high resistance: to pass a meaningful amount of current through an object with a high resistance, a high voltage must be used.

Everything has resistance

Every object in the universe has a value of resistance, even you!

Electrical conductors are materials with a high conductivity, so as a result a wire made from an electrical conductor will have a very low resistance. This means that significant current will flow through it even at a very low voltage. That s why the voltage in a bolt of lightning has to be so high up in the millions in fact: air is so highly resistive that this extremely high voltage is required to ionise it and allow for it to conduct electricity.

Let s apply this knowledge to the human body

The human body isn t made out of metal, as we know. It s made out of flesh and bone, both of which are electrical insulators with an extremely high resistance. So if we could pass an electrical surge through the body at a voltage high enough to allow the body to fully conduct 20 milliamps, it will be a lethal shock. The entire body begins to conduct electricity at 500 volts, so a 500 volt pulse at 20 milliamps would potentially be able to cause enough current to pass through your body, and be lethal. So while it s the 20 milliamps of current that are deadly, the current wouldn t be able to do the damage that it does without the voltage allowing it to flow through the entire body.

The voltage itself in an electric surge is not enough to be dangerous. In fact, if you had 10 million volts flowing through you and the current was limited to an extremely low value (less than a milliamp), you would likely not be harmed.

So what have we learned?

So it s the voltage which allows the current to kill. If it wasn t for mains electricity having such a high voltage, it wouldn t be anywhere near as dangerous. lt;/p>
In fact, much like with the high voltage/low current example seen at the end of the last paragraph, the same idea works the other way: An extremely high current with an extremely low voltage wouldn t be able to cause any noticeable damage to us since the voltage would simply be too low for the current to pass through us.