I can't understand why 20 000 Volts of ESD has very low current but 110V/200V from the power outlet on the wall can kill you and the current is a lot higher than ESD. When you have 20 000 volts potential difference between your body and the door handle this means that the electrons in your body are a lot more than in the door handle, so there will be big discharge. For example 20kV means that you have 100 000 electrons more than the door handle and they will move from you to it for a short amount of time. If we follow the example, the power outlet has 220V and this is about 100 times lower than 20 000V, so the electrons should be 100 times less (1 000 electrons). So if you touch the live wire in the power outlet the current should be less than the current in 20 000V of ESD. Where am I wrong? Please, explain it with example :)
-
Ohm's law: V = I*R. Voltage is equal to current times resistance.
Resistance is a measure of a material's ability to block the flow of charge. Air is extremely highly resistive -- therefore, even managing to get a small current through the air (micro-amps) requires a huge voltage. The voltage between the doorknob and your hand is tens of thousands of volts, but the current is small because it has to go through the air, so the voltage drop is almost entirely across the air instead of across you. I've tried to measure the air's resistivity before just for fun, and it goes way past 10 mega-ohms even at a millimeter distance.
Your skin, on the other hand, is fairly conductive. When you touch a live wire, it isn't the air that has to conduct the electricity, it's your skin and your body. Your body's resistance is very low, certainly nowhere near mega-ohms. With that V=IR formula, your small resistance means the current can be very high even with a relatively low voltage.
Resistance is a measure of a material's ability to block the flow of charge. Air is extremely highly resistive -- therefore, even managing to get a small current through the air (micro-amps) requires a huge voltage. The voltage between the doorknob and your hand is tens of thousands of volts, but the current is small because it has to go through the air, so the voltage drop is almost entirely across the air instead of across you. I've tried to measure the air's resistivity before just for fun, and it goes way past 10 mega-ohms even at a millimeter distance.
Your skin, on the other hand, is fairly conductive. When you touch a live wire, it isn't the air that has to conduct the electricity, it's your skin and your body. Your body's resistance is very low, certainly nowhere near mega-ohms. With that V=IR formula, your small resistance means the current can be very high even with a relatively low voltage.
-
the current is not limited in the wall outlet - fusing usually for a wall outlet is between 15 and 20 amps. a static discharge has a great amount of difference in potential but the current is limited - it is of short duration also,
-
The standard ESD model is a cap charged to a high voltage in series with a resistor. The resistor limits the current. The thing that is important is how much energy is deliverd to the device (or thing) that comes in contact with the charged cap and resistor.