Why is it safe to touch the terminals of a car 12V battery with bare hands?
As we all know, it is current, not voltage, that causes death. However, voltage (similar to pressure) is required to flow current in a conductor. It indicates that amperes, not volts, kill. The question here is why a 12V battery (household or automotive) is safe even at high amperage. Let’s look at why a 12V vehicle battery does not electrocute or harm you, and whether there is a risk of electrocution from a 12V car battery.
Keep in mind that the battery’s stored voltage is DC. There is a slight difference between AC and DC, but the effect of electric shock on the human body is significant, thus which is more harmful, AC or DC?
According to the article, you may have made direct contact with both terminals of the battery with bare hands without receiving an electric shock. Right? The rationale for this magic is as follows.
Actually, it is the current that causes saver shock, but electric current cannot flow unless there is sufficient pressure (voltage). The second characteristic is resistance, which practically every material possesses. The human body, too, has some resistance.
100,000 Ohms in dry condition and 1000 ohms in wet condition
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Now suppose a human body torches both terminals of battery (positive and negative) with bare hands.
According to Ohm’s law:
Dry Condition where human body resistance = 1 × 105 Ω)
I = V ÷ R
I = 12V ÷ 100,000Ω
I = 0.12 mA
Throughout Wet Condition where human body resistance = 1k Ω)
I = V ÷ R
I = 12V ÷ 1000Ω
I = 12 mA
Upon reviewing the calculations, it appears that the 0.12 mA of current that results from touching a 12V battery in a dry condition is not significant, as the low voltage is unable to push the current through the body’s high resistance, which can be up to 100kΩ. This phenomenon is similar to aluminum smelters and welding machines, where high amperage is required, but only a few volts are used.
Conversely, a high voltage with low amperage, such as that generated by a tabletop Van de Graaff generator, does not pose a significant threat of harm, as it is the combination of both voltage and current that determines the severity of an electric shock.
However, in the case of touching a battery with wet hands, such as during rain or when sweating, the resistance of the human body decreases to around 1kΩ, potentially allowing for a greater current to flow through the body. A current of 12mA can cause painful sensations, and a current of 9-25 mA can cause muscular contraction, indicating that the 12 mA current falls within the range of potential danger.
It is important to note that the above calculations are based on fully wet conditions, such as standing in the rain, and that there may be no risk of electric shock with slightly damp hands or if the battery is not fully charged. However, it is always best to avoid touching battery terminals with bare hands in wet conditions to minimize the risk of harm.
Good To Know:
- The average resistance of a human body in dry conditions is approximately 100,000Ω.
- In wet conditions, the resistance of a human body drops to 1000Ω.
- A voltage above 50V in dry conditions and 25V in wet conditions is sufficient to cause a person to experience an electric shock.
- A current of 30mA is enough for respiratory paralysis, and 75-100mA can cause ventricular fibrillation, characterized by rapid and ineffective heartbeat.
- Currents higher than 300mA are fatal and can cause death in seconds.
- Currents between 4.5 to 10A can lead to cardiac arrest, severe burns, and eventual death.
- The severity of an electric shock is primarily determined by the electrical power, which is a combination of both voltage and current, where voltage acts as pressure, pushing electric current (the flow of charge) through the body, resulting in an electric shock.