How many milliamperes of electric current can cause muscle contraction and loss of control if it passes through the human body?

The correct answer highlights that an electric current of 15-20 milliamperes (mA) is capable of causing muscle contraction and loss of control when it passes through the human body. This range is significant because it is at this level that the electrical stimulus becomes strong enough to interfere with the normal functioning of the nervous system, particularly affecting voluntary muscle control.

When the current flowing through the body reaches this level, it can lead to involuntary muscle contractions, making it difficult for a person to release their grip from a live electrical source. This can be particularly dangerous in situations where one might be in contact with high-voltage equipment, as the inability to let go can result in prolonged exposure and increased risk of severe injury or fatality.

Lower currents, such as those below 15 mA, typically do not produce the same level of physiological effects, allowing most individuals to maintain some level of control over their muscles. Understanding these thresholds is crucial for safety training and electrical work practices, therefore informing safety measures when working with or around electrical equipment.