There are many myths and misunderstandings about electricity and electrical safety. For example, it is a myth based on a partial truth that it is the voltage that kills you. In reality it is the amount of current that passes through your body that kills you and it does not take all that much current to kill you. The amount of current that it takes to kill a human being depends on the path the current travels through the body. The myth is based on a partial truth because current is directly proportional to voltage and inversely proportional to resistance; resistance being the opposition to current flow. For those of you who remember your high school physics classes, you will remember this basic Ohms Law Formula I=E/R, where I equal the electric current in Amperes, E equal the electrical force in Volts, and R equals the electrical resistance in Ohms. This formula is another way of saying that the current is directly proportional to the electrical pressure (Voltage) and inversely proportional to the electrical resistance (the opposition to the flow of current) measured in Ohms. Fix this concept in mind because understanding it is critical to understanding what follows.
The Opposition to the Flow of Current Through the Body.
The amount of resistance that your body provides to the flow of electric current through it depends on external factors as well as to internal factors. Dry skin offers a higher resistance to electric current flow than wet skin. The amount of resistance decreases as the area in contact with current source increases. Resistance decreases as the pressure between the body and the current source increases. The duration of the current through the body and the frequency of the electric current also plays a significant role in the effects the shock has on the person's body. The effects of an electric shock can run the gamut from nothing more than a mild tingling sensation to cardiac arrest and death.
The Dangers of Low Voltage Shocks.
As a rule, the skin provides enough resistance to voltages below 50 volts to keep the current flowing through the body to a relatively safe level. Many regulatory agencies, like The Office Of Energy in Western Australia, classify Extra Low Voltage, or ELV, as 0 to 50 volts. The Office Of Energy does not require an electrical license when working on equipment operating up to 50 volts. Once the voltage exceeds 50 volts, the resistance to the flow of electric current through the human body decreases rapidly, because of the dangers of working with Low Voltages (voltages between 50-volts and 1000-volts) most regulatory bodies require those working with it be licensed. The one3 exception to that rule, at least here in the United States, is for home owners working on their own residence. Nevertheless, the DIY electrician must follow the same rules as a licensed electrician would have to—obtain required permits, have required inspections performed, perform work according to electrical codes, etc.
As a rule, the skin provides enough resistance to voltages below 50 volts to keep the current flowing through the body to a relatively safe level, but that does not mean you cannot be killed by ELV. Under the right conditions, ELV can be just as fatal as Low Voltage (50 to 1000-volts) or deadly as High Voltage, voltages in excess of 1000-volt
Involuntary muscular contraction.
Even shocks caused by ELV can cause involuntary muscular contraction which can cause a person working on a ladder to fall off. The fall itself can lead to more serious injuries, even death. Involuntary muscular contractions can also
lead to a person being unable to free themselves from the source of the electric current i.e. a bare electric wire.
Death results from ventricular fibrillation.
Death by electrocution is caused when an electric shock disrupts the timing of the heart muscle contractions which disrupts the flow of oxygenated blood to brain resulting in death. Once fibrillation has set in, it is a rare event when the heart can return to beating normally without the application of a medical defibrillator, such as the ones carried by emergency medical teams.
How much current does it take to cause fibrillation?
OK, hang on to your seats because this is going to be a real shocker, all it takes is a current of 50 to 200 mA (milliamperes) to flow through your heart to cause fibrillation of the heart muscles. One milliampere is equal to 1/1000 of an ampere. It takes 1/5 the current it takes to light a 100 Watt incandescent light bulb to kill you. The human skin exhibits a resistance of 100,000 Ohms when dry and only 1,000 Ohms when wet. If wet, a voltage between 50 and 200-volts can kill you. If the skin is completely moisture free, it will take a voltage between 5000 and 20,000-volts to kill you. Since ones skin is never completely moisture free, the voltage needed to cause fibrillation falls somewhere in between those extremes.