CABLE SIZE & CURRENT CARRYING CAPACITY OF CABLE

 

Voltage or current which is more dangerous

The difference between electricity and current is confusing for many people who do not have a background in electrical science / engineering. How many times have we heard the phrase “touch the cable with x volts running”, which discourages electrical engineers.

To understand the difference, consider water. The water itself is like an electric charger, which always does nothing but, if you lift it up to the top, it gets a potent power and wants to flow down; voltage is often referred to as power for a reason. You will only get a flow if you have a difference (possible), in other words a voltage, between a high water tank AND a low surface AND both are connected to a pipe of some kind. High power can only "kill" you if you allow current to flow. A “pipe” can be anything that electricity can flow into, say, a telephone, or it can be your body.

Now, if you connect a small pipe to your high water tank, that pipe has high resistance to flow and you will only get a small squirt of water at the end. The flow rate, "currently" (also called for a reason), is small although the potential difference is high and that small current will not harm it.

If on the other hand you connect a large fat sluice pipe (with "low resistance") to that water tank, you will get a large flow rate and it will drop you to your feet.

So, go back to electricity. Voltage is not something that kills you, it is now. The reason why high voltages are dangerous is because they have great potential to kill you. There is no danger of the current unless you put yourself in the current position by connecting the world's highest energy (or something) with your body.

So 240V (here in the UK) is dangerous because it is connected to your body down to earth with resistance (say) 1,200 ohms or more will push the current 200mA for you enough to kill you. If you happen to be standing on a rubber mat, then you can escape because now the resistance on the road is high so it is currently low even though the voltage is the same.

On the other hand your USB phone charger probably emits about 1A (enough to kill you) but that is not dangerous because a) it passes through the cable and does not pass through you and b) because it is close. 5V therefore, if you plug it into your body resistance which is much higher than your phone, it will produce a small current (about 4mA or less) that will not hurt you at all.

So it is a deadly current but the electrical power is dangerous.

Having said that, birds can safely sit on top of power lines because even though those may be '000s of volts, the air gap resistance between them and the ground is never ending so there is no current flow (backwards. In my water simulation, the water tank is very high). but no pipe is connected to it, the bird is sitting on top with the tank).

I get to think about it about the height of the water and the pipes making it very clear to the average person.