The question of whether voltage (volts) or current (amperes) is responsible for electrical injury is a common point of confusion. It is a misconception that high voltage alone determines the danger of an electrical shock. This article clarifies the distinct roles of voltage, current, and resistance in the context of human exposure to electricity, explaining the science behind why electrical currents cause physiological harm.
Defining Electrical Fundamentals
Electricity is governed by three concepts: voltage, current, and resistance. Voltage is the measure of electrical potential difference between two points, acting as the driving force that pushes the charge. Using a water analogy, voltage is like the pressure in a hose.
Current, measured in amperes (amps), is the actual rate of flow of electrical charge, which is the movement of electrons. Resistance, measured in ohms, is the opposition to this flow of current. These three elements are linked and must all be considered to understand the risk of electrical shock.
Why Current (Amps) Causes Physiological Harm
The definitive cause of injury and death is electrical current, measured in amperes or, more commonly, milliamperes (mA). The human body is fundamentally electrochemical, relying on precise electrical impulses for functions like nerve signals and muscle contractions. When an external current passes through the body, it disrupts these natural signals, leading to physiological damage.
A dangerous current can overload the nervous system, causing involuntary muscle contraction, often called “tetanization.” This contraction can prevent a person from letting go of the electrical source, increasing the duration of exposure and the resulting harm. The most serious effect occurs when current passes through the chest and disrupts the heart’s rhythm, inducing ventricular fibrillation. This condition causes the heart’s ventricles to twitch uncoordinately instead of pumping blood effectively, leading to circulatory failure and death.
The Role of Voltage and Resistance in Current Flow
While current is the direct cause of injury, voltage is the necessary driving force that pushes current through the body’s resistance. This relationship is described by Ohm’s Law, which states that current equals voltage divided by resistance. High voltage is dangerous because it has the potential to overcome the body’s natural resistance and generate a lethal current.
The total resistance of the human body is not fixed and is significantly affected by the skin. Dry, calloused skin can offer resistance exceeding 100,000 ohms, providing substantial protection. If the skin is wet from water or sweat, however, its resistance can drop dramatically, sometimes to as low as 1,000 ohms. This allows a much higher current to flow at the same voltage. The path the current takes is also a determinant, as a hand-to-hand or hand-to-foot path is hazardous because it often puts the heart directly in the current’s path.
Understanding Dangerous Current Thresholds
The severity of an electrical shock relates directly to the magnitude of the current and the duration of exposure. Currents below 1 milliampere (mA) are generally imperceptible to humans. A current of about 5 mA typically results in a mild, slightly painful shock, but the individual can still let go of the conductor.
The “let-go” threshold, where involuntary muscle contraction prevents release, is typically between 9 and 30 mA for adult men and 6 to 25 mA for women. A current between 75 mA and 100 mA is often the lethal range because it is highly likely to cause ventricular fibrillation if the current passes through the heart. Currents above 200 mA can sometimes cause the heart muscle to clamp shut. While this can offer a higher chance of survival after the shock ends, the intense current often causes severe electrical burns and tissue damage as a secondary effect.