1. A comparison of the dangers of an electric shock from a 240V AC mains supply and various DC voltages from appliances on the body.
Everyday in the home we are exposed to two different forms of electricity AC and DC. Electricity from the mains supply is 240V alternating current (AC) that alternates around 50 times per second and ranges from -340V to 340V. Appliances in the house then convert it from AC to direct current (DC) in a number of voltages depending on the appliance. Both AC and DC currents cause an electric shock. An electric shock is the sudden discharge of electricity though the body and can cause the disruption of the bodily systems. The (Types of current) danger of an electric shock depends on the strength of the current, the course of the current through the body and the form, AC or DC. The conditions, affected by a number of factors such as moisture and duration of exposure, also change the danger of a shock. However the difference of the danger of an electric shock from an AC or DC in the same circumstances (including current strength) is affected solely by the current flow and direction.
An electric shock from an AC is generally more dangerous than that of a DC due to the body’s higher reactivity to the alternating current. This is evident because an AC of 1< mA entering the hand can be felt whereas a DC of 5< mA entering the hand can be felt. AC because of the alternating direction is constantly changing the current running through a certain point and in the body this can cause spasms, numbness and loss of control. AC can produce extended muscle contraction (Tetanus) fixing the victim to the wire prolonging exposure and therefore making it dangerous, this occurs in an AC stronger than 15 mA, which is called a ‘let go’ threshold or current. DC because it holds a constant current is more likely to cause a single convulsive contraction that often pushes the victim away from the currents source; however DC of greater than 75 mA will cause tetanus. Therefore danger of being frozen to a circuit is greater in AC than DC.
AC because of the changing frequency has a tendency to put the hearts pacemaker neuron into a condition of fibrillation, which is when the heart rather than pumping blood fluctuates quickly. Generally it takes an AC more than 65 mA to cause fibrillation. DC is more likely to shock the heart and stop it from beating, which occurs in currents 200 mA or more. When the current ceases to flow through the body the heart has a better chance of regaining a normal beating pattern if it is stopped rather than fibrillating thus why defibrillating equipment uses DC. Therefore the danger of death from AC is greater than that of DC.
Strong currents also have a tendency of traveling over the surface of the body missing organs reducing chance of death but causing scarring and burns.
In the household 240V AC mains supply tends to be more dangerous than DC from appliances because of the body’s higher reactivity to alternating currents. The dangers of electric shock increase with stronger currents, longer duration, path through the internal organs, and increased voltage. Both types of currents are very dangerous and in stronger currents death is the likely result so the other factors are irrelevant.
A comparison of the currents needed in AC and DC to cause certain effects on the body A comparison of increased current and the effects